Oxidation state (English Wikipedia)

Analysis of information sources in references of the Wikipedia article "Oxidation state" in English language version.

refsWebsite

Global rank English rank

179doi.org

2^nd place

61nih.gov

4^th place

50harvard.edu

18^th place

17^th place

24semanticscholar.org

11^th place

8^th place

15worldcat.org

5^th place

13web.archive.org

1^st place

5acs.org

1,248^th place

1,104^th place

4handle.net

102^nd place

76^th place

4books.google.com

3^rd place

4uwaterloo.ca

3,153^rd place

2,332^nd place

3d-nb.info

511^th place

7,028^th place

3chemistryviews.org

low place

3researchgate.net

120^th place

125^th place

3zenodo.org

621^st place

380^th place

3iupac.org

538^th place

863^rd place

3gsi.de

low place

2archive.org

6^th place

2ghostarchive.org

32^nd place

21^st place

2osti.gov

2,036^th place

1,254^th place

2caltech.edu

887^th place

714^th place

2dtu.dk

low place

8,755^th place

2nist.gov

355^th place

454^th place

2springer.com

274^th place

309^th place

2unt.edu

1,336^th place

769^th place

2psi.ch

low place

1libretexts.org

3,627^th place

2,467^th place

1ed.ac.uk

1,871^st place

1,234^th place

1wiley.com

222^nd place

297^th place

1science.org

1,160^th place

737^th place

1uni-kassel.de

low place

1znaturforsch.com

low place

1sciencedirect.com

149^th place

178^th place

1elsevier.com

610^th place

704^th place

1aip.org

2,204^th place

1,735^th place

1researchwithrutgers.com

low place

1webelements.com

3,527^th place

low place

1nature.com

234^th place

397^th place

1iaea.org

1,168^th place

1,193^rd place

1cenmag.org

low place

1degruyter.com

1,425^th place

1,138^th place

1scitation.org

4,352^nd place

3,229^th place

1nevada.edu

low place

1chemie-master.de

low place

1escholarship.org

1,523^rd place

976^th place

1yale.edu

565^th place

460^th place

acs.org (Global: 1,248^th place; English: 1,104^th place)

pubs.acs.org

Br(II) is known to occur in bromine monoxide radical; see Kinetics of the bromine monoxide radical + bromine monoxide radical reaction
SmB₆⁻ cluster anion has been reported and contains Sm in rare oxidation state of +1; see Paul, J. Robinson; Xinxing, Zhang; Tyrel, McQueen; Kit, H. Bowen; Anastassia, N. Alexandrova (2017). "SmB₆^– Cluster Anion: Covalency Involving f Orbitals". J. Phys. Chem. A. 121 (8): 1849–1854. Bibcode:2017JPCA..121.1849R. doi:10.1021/acs.jpca.7b00247. PMID 28182423. S2CID 3723987..
U(I) has been observed in [U(η⁵-C₅ⁱPr₅)₂]⁻, see Barluzzi, Luciano; Giblin, Sean R.; Mansikkamäki, Akseli; Layfield, Richard A. (2022). "Identification of Oxidation State +1 in a Molecular Uranium Complex". J. Am. Chem. Soc. 144 (40): 18229–18233. doi:10.1021/jacs.2c06519. PMID 36169550. S2CID 252567088. Retrieved 13 July 2023.

cen.acs.org

All the lanthanides, except Pm, in the +2 oxidation state have been observed in organometallic molecular complexes, see Lanthanides Topple Assumptions and Meyer, G. (2014). "All the Lanthanides Do It and Even Uranium Does Oxidation State +2". Angewandte Chemie International Edition. 53 (14): 3550–51. doi:10.1002/anie.201311325. PMID 24616202.. Additionally, all the lanthanides (La–Lu) form dihydrides (LnH₂), dicarbides (LnC₂), monosulfides (LnS), monoselenides (LnSe), and monotellurides (LnTe), but for most elements these compounds have Ln³⁺ ions with electrons delocalized into conduction bands, e. g. Ln³⁺(H⁻)₂(e⁻).

acs.org

"Antoine Laurent Lavoisier The Chemical Revolution – Landmark – American Chemical Society". American Chemical Society. Archived from the original on 5 January 2021. Retrieved 14 July 2018.

aip.org (Global: 2,204^th place; English: 1,735^th place)

pubs.aip.org

Ma, Wen; Herbert, F. William; Senanayake, Sanjaya D.; Yildiz, Bilge (2015-03-09). "Non-equilibrium oxidation states of zirconium during early stages of metal oxidation". Applied Physics Letters. 106 (10). Bibcode:2015ApPhL.106j1603M. doi:10.1063/1.4914180. hdl:1721.1/104888. ISSN 0003-6951.

archive.org (Global: 6^th place; English: 6^th place)

Petrucci, R. H.; Harwood, W. S.; Herring, F. G. (2002). General Chemistry (8th ed.). Prentice-Hall. ISBN 978-0-13-033445-9.^{[ISBN missing]}
Whitten, K. W.; Galley, K. D.; Davis, R. E. (1992). General Chemistry (4th ed.). Saunders. p. 147. ISBN 978-0-03-075156-1.^{[ISBN missing]}

books.google.com (Global: 3^rd place; English: 3^rd place)

B(−1) has been observed in magnesium diboride (MgB₂), see Keeler, James; Wothers, Peter (2014). Chemical Structure and Reactivity: An Integrated Approach. Oxford University Press. ISBN 978-0-19-960413-5.
In(−2) has been observed in Na₂In, see [1], p. 69.
Harding, Charlie; Johnson, David Arthur; Janes, Rob (2002). Elements of the p block. Great Britain: Royal Society of Chemistry. pp. 93–94. ISBN 0-85404-690-9.
Rn(II) and Rn(VI) are known in RnF₂ and RnO₃, respectively; see Sykes, A. G. (1998). "Recent Advances in Noble-Gas Chemistry". Advances in Inorganic Chemistry. Vol. 46. Academic Press. pp. 91–93. ISBN 978-0-12-023646-6. Retrieved 2012-11-02.

caltech.edu (Global: 887^th place; English: 714^th place)

authors.library.caltech.edu

Moret, Marc-Etienne; Zhang, Limei; Peters, Jonas C. (2013). "A Polar Copper–Boron One-Electron σ-Bond". J. Am. Chem. Soc. 135 (10): 3792–3795. Bibcode:2013JAChS.135.3792M. doi:10.1021/ja4006578. PMID 23418750.
Pauling, L. (1948). "The modern theory of valency". J. Chem. Soc. 1948: 1461–1467. doi:10.1039/JR9480001461. PMID 18893624. Archived from the original on 2021-12-07. Retrieved 2021-11-22.

cenmag.org (Global: low place; English: low place)

2014.cenmag.org

Ir(VII) has been observed in [(η²-O₂)IrO₂]⁺; see C&EN: Iridium dressed to the nines.

chemie-master.de (Global: low place; English: low place)

Am(VII) has been observed in AmO3−5; see Americium, Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010 and Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1265. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.

chemistryviews.org (Global: low place; English: low place)

"New Type of Zero-Valent Tin Compound". Chemistry Europe. 27 August 2016.
"New Type of Zero-Valent Tin Compound". Chemistry Europe. 27 August 2016.
"New Type of Zero-Valent Tin Compound". Chemistry Europe. 27 August 2016.

d-nb.info (Global: 511^th place; English: 7,028^th place)

Schroeder, Melanie, Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden (in German), p. 139, archived from the original on 2020-08-06, retrieved 2020-02-24
B(−5) has been observed in Al₃BC, see Schroeder, Melanie. "Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden" (in German). p. 139.
Bi(−2) and Bi(−1) occur in Zintl phases, e.g. (Ca²⁺)₂₂[Bi₄]⁴⁻([Bi₂]⁴⁻)₄[Bi³⁻]₈; see Ponou, Siméon (2006). "Germanides, Germanide-Tungstate Double Salts and Substitution Effects in Zintl Phases". Technische Universität München. Lehrstuhl für Anorganische Chemie mit Schwerpunkt Neue Materialien. p. 68.

degruyter.com (Global: 1,425^th place; English: 1,138^th place)

Brauer, G.; Haucke, W. (1936-06-01). "Kristallstruktur der intermetallischen Phasen MgAu und MgHg". Zeitschrift für Physikalische Chemie. 33B (1): 304–310. doi:10.1515/zpch-1936-3327. ISSN 2196-7156. MgHg then lends itself to an oxidation state of +2 for Mg and -2 for Hg because it consists entirely of these polar bonds with no evidence of electron unpairing. (translated)

doi.org (Global: 2^nd place; English: 2^nd place)

Wang, G.; Zhou, M.; Goettel, G. T.; Schrobilgen, G. J.; Su, J.; Li, J.; Schlöder, T.; Riedel, S. (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Yu, Haoyu S.; Truhlar, Donald G. (2016). "Oxidation State 10 Exists". Angewandte Chemie International Edition. 55 (31): 9004–9006. doi:10.1002/anie.201604670. PMID 27273799.
Karen, P.; McArdle, P.; Takats, J. (2016). "Comprehensive definition of oxidation state (IUPAC Recommendations 2016)". Pure Appl. Chem. 88 (8): 831–839. doi:10.1515/pac-2015-1204. hdl:10852/59520. S2CID 99403810.
Karen, P.; McArdle, P.; Takats, J. (2014). "Toward a comprehensive definition of oxidation state (IUPAC Technical Report)". Pure Appl. Chem. 86 (6): 1017–1081. doi:10.1515/pac-2013-0505.
IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "Oxidation state". doi:10.1351/goldbook.O04365
IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "Oxidation number". doi:10.1351/goldbook.O04363
Karen, Pavel (2015). "Oxidation State, A Long-Standing Issue!". Angewandte Chemie International Edition. 54 (16): 4716–4726. doi:10.1002/anie.201407561. PMC 4506524. PMID 25757151.
Hooydonk, G. Van (1974-05-01). "O n an Ionic Approximation to Chemical Bonding". Zeitschrift für Naturforschung A. 29 (5): 763–767. Bibcode:1974ZNatA..29..763H. doi:10.1515/zna-1974-0517. ISSN 1865-7109.
"Oxidation state". The IUPAC Compendium of Chemical Terminology: The Gold Book. 2009. doi:10.1351/goldbook.O04365. ISBN 978-0-9678550-9-7.
Muir, K. W.; Ibers, J. A. (1969). "The structure of chlorocarbonyl(sulfur dioxide)bis(triphenylphosphine)rhodium, (RhCl(CO)(SO2)(P(C6H5)3 2)". Inorg. Chem. 8 (9): 1921–1928. doi:10.1021/ic50079a024.
Martinie, R. J.; Bultema, J. J.; Wal, M. N. V.; Burkhart, B. J.; Griend, D. A. V.; DeCock, R. L. (2011). "Bond order and chemical properties of BF, CO, and N₂". J. Chem. Educ. 88 (8): 1094–1097. Bibcode:2011JChEd..88.1094M. doi:10.1021/ed100758t.
Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 27–28. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Li(–1) has been observed in the gas phase; see R. H. Sloane; H. M. Love (1947). "Surface Formation of Lithium Negative Ions". Nature. 159 (4035): 302–303. Bibcode:1947Natur.159..302S. doi:10.1038/159302a0.
Be(−2) has been observed in ZrBe₂ and HfBe₂, see Goesten, Maarten G. (2022). "Be–Be π-Bonding and Predicted Superconductivity in MBe2 (M=Zr, Hf)". Angew. Chem. Int. Ed. 61 (4) e202114303. doi:10.1002/anie.202114303.
Berthold, Chantsalmaa; Maurer, Johannes; Klerner, Lukas; Harder, Sjoerd; Buchner, Magnus R. (2024-05-31). "Formation, Structure and Reactivity of a Beryllium(0) Complex with Mg^δ+−Be^δ− Bond Polarization". Angewandte Chemie International Edition. 63 (35) e202408422. doi:10.1002/anie.202408422.
Boronski, Josef T.; Crumpton, Agamemnon E.; Wales, Lewis L.; Aldridge, Simon (2023-06-16). "Diberyllocene, a stable compound of Be(I) with a Be–Be bond". Science. 380 (6650): 1147–1149. Bibcode:2023Sci...380.1147B. doi:10.1126/science.adh4419. ISSN 0036-8075. PMID 37319227. S2CID 259166086.
Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A. (2012). "Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond". Science. 336 (6087): 1420–2. Bibcode:2012Sci...336.1420B. doi:10.1126/science.1221138. PMID 22700924. S2CID 206540959.
Zhang, K.Q.; Guo, B.; Braun, V.; Dulick, M.; Bernath, P.F. (1995). "Infrared Emission Spectroscopy of BF and AIF" (PDF). J. Molecular Spectroscopy. 170 (1): 82. Bibcode:1995JMoSp.170...82Z. doi:10.1006/jmsp.1995.1058.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Tetrazoles contain a pair of double-bonded nitrogen atoms with oxidation state 0 in the ring. A Synthesis of the parent 1H-tetrazole, CH₂N₄ (two atoms N(0)) is given in Henry, Ronald A.; Finnegan, William G. (1954). "An Improved Procedure for the Deamination of 5-Aminotetrazole". Journal of the American Chemical Society. 76 (1): 290–291. Bibcode:1954JAChS..76..290H. doi:10.1021/ja01630a086. ISSN 0002-7863.
Gold heptafluoride, synthesized at low temperature, is calculated to be a complex of molecular fluorine with gold pentafluoride, with F-F bonding in the F₂ evidenced by IR spectroscopy; see Himmel, Daniel; Riedel, Sebastian (2007-05-31). "After 20 Years, Theoretical Evidence That "AuF₇" Is Actually AuF₅·F₂". Inorganic Chemistry. 46 (13): 5338–5342. doi:10.1021/ic700431s. PMID 17511450.
Ne(0) has been observed in Cr(CO)₅Ne; see Perutz, Robin N.; Turner, James J. (August 1975). "Photochemistry of the Group 6 hexacarbonyls in low-temperature matrices. III. Interaction of the pentacarbonyls with noble gases and other matrices". Journal of the American Chemical Society. 97 (17): 4791–4800. Bibcode:1975JAChS..97.4791P. doi:10.1021/ja00850a001.
Mg(0) has been synthesized in a compound containing a Na₂Mg₂²⁺ cluster coordinated to a bulky organic ligand; see Rösch, B.; Gentner, T. X.; Eyselein, J.; Langer, J.; Elsen, H.; Li, W.; Harder, S. (2021). "Strongly reducing magnesium(0) complexes". Nature. 592 (7856): 717–721. Bibcode:2021Natur.592..717R. doi:10.1038/s41586-021-03401-w. PMID 33911274. S2CID 233447380
Bernath, P. F.; Black, J. H. & Brault, J. W. (1985). "The spectrum of magnesium hydride" (PDF). Astrophysical Journal. 298: 375. Bibcode:1985ApJ...298..375B. doi:10.1086/163620.. See also Low valent magnesium compounds.
Al(−2) has been observed in Sr₁₄[Al₄]₂[Ge]₃, see Wemdorff, Marco; Röhr, Caroline (2007). "Sr₁₄[Al₄]₂[Ge]₃: Eine Zintl-Phase mit isolierten [Ge]^4–- und [Al₄]^8–-Anionen / Sr₁₄[Al₄]₂[Ge]₃: A Zintl Phase with Isolated [Ge]^4–- and [Al₄]^8– Anions". Zeitschrift für Naturforschung B (in German). 62 (10): 1227. doi:10.1515/znb-2007-1001. S2CID 94972243.
Al(–1) has been reported in Na₅Al₅; see Haopeng Wang; Xinxing Zhang; Yeon Jae Ko; Andrej Grubisic; Xiang Li; Gerd Ganteför; Hansgeorg Schnöckel; Bryan W. Eichhorn; Mal-Soon Lee; P. Jena; Anil K. Kandalam; Boggavarapu Kiran; Kit H. Bowen (2014). "Aluminum Zintl anion moieties within sodium aluminum clusters". The Journal of Chemical Physics. 140 (5). Bibcode:2014JChPh.140e4301W. doi:10.1063/1.4862989.
Unstable carbonyl of Al(0) has been detected in reaction of Al₂(CH₃)₆ with carbon monoxide; see Sanchez, Ramiro; Arrington, Caleb; Arrington Jr., C. A. (December 1, 1989). "Reaction of trimethylaluminum with carbon monoxide in low-temperature matrixes". American Chemical Society. 111 (25): 9110-9111. Bibcode:1989JAChS.111.9110S. doi:10.1021/ja00207a023. OSTI 6973516.
Dohmeier, C.; Loos, D.; Schnöckel, H. (1996). "Aluminum(I) and Gallium(I) Compounds: Syntheses, Structures, and Reactions". Angewandte Chemie International Edition. 35 (2): 129–149. doi:10.1002/anie.199601291.
Tyte, D. C. (1964). "Red (B2Π–A2σ) Band System of Aluminium Monoxide". Nature. 202 (4930): 383. Bibcode:1964Natur.202..383T. doi:10.1038/202383a0. S2CID 4163250.
Ram, R. S.; et al. (1998). "Fourier Transform Emission Spectroscopy of the A2D–X2P Transition of SiH and SiD" (PDF). J. Mol. Spectr. 190 (2): 341–352. doi:10.1006/jmsp.1998.7582. PMID 9668026.
Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; King, R. Bruce; Schaefer, Iii; Schleyer, Paul v. R.; Robinson, Gregory H. (2008). "Carbene-Stabilized Diphosphorus". Journal of the American Chemical Society. 130 (45): 14970–1. Bibcode:2008JAChS.13014970W. doi:10.1021/ja807828t. PMID 18937460.
Ellis, Bobby D.; MacDonald, Charles L. B. (2006). "Phosphorus(I) Iodide: A Versatile Metathesis Reagent for the Synthesis of Low Oxidation State Phosphorus Compounds". Inorganic Chemistry. 45 (17): 6864–74. doi:10.1021/ic060186o. PMID 16903744.
Ar(0) has been observed in argon fluorohydride (HArF) and ArCF₂²⁺, see Lockyear, J.F.; Douglas, K.; Price, S.D.; Karwowska, M.; et al. (2010). "Generation of the ArCF₂²⁺ Dication". Journal of Physical Chemistry Letters. 1: 358. doi:10.1021/jz900274p.
John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Calcium(I) has been obtained as a dinuclear organometallic complex with an arene dianion, see Krieck, Sven; Görls, Helmar; Yu, Lian; Reiher, Markus; Westerhausen, Matthias (2009). "Stable "Inverse" Sandwich Complex with Unprecedented Organocalcium(I): Crystal Structures of [(thf)2Mg(Br)-C6H2-2,4,6-Ph3] and [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3]". Journal of the American Chemical Society. 131 (8): 2977–2985. doi:10.1021/ja808524y..
Cloke, F. Geoffrey N.; Khan, Karl & Perutz, Robin N. (1991). "η-Arene complexes of scandium(0) and scandium(II)". J. Chem. Soc., Chem. Commun. (19): 1372–1373. doi:10.1039/C39910001372.
Smith, R. E. (1973). "Diatomic Hydride and Deuteride Spectra of the Second Row Transition Metals". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 332 (1588): 113–127. Bibcode:1973RSPSA.332..113S. doi:10.1098/rspa.1973.0015. S2CID 96908213.
McGuire, Joseph C.; Kempter, Charles P. (1960). "Preparation and Properties of Scandium Dihydride". Journal of Chemical Physics. 33 (5): 1584–1585. Bibcode:1960JChPh..33.1584M. doi:10.1063/1.1731452.
Ti(-2) is known in Ti(CO)2−6; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Jilek, Robert E.; Tripepi, Giovanna; Urnezius, Eugenijus; Brennessel, William W.; Young, Victor G. Jr.; Ellis, John E. (2007). "Zerovalent titanium–sulfur complexes. Novel dithiocarbamato derivatives of Ti(CO)₆:[Ti(CO)₄(S₂CNR₂)]⁻". Chem. Commun. (25): 2639–2641. doi:10.1039/B700808B. PMID 17579764.
Andersson, N.; et al. (2003). "Emission spectra of TiH and TiD near 938 nm". J. Chem. Phys. 118 (8): 10543. Bibcode:2003JChPh.118.3543A. doi:10.1063/1.1539848.
V(–3) is known in V(CO)3−5; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
V(0) is known in V(CO)₆; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Cr(–4) is known in Na₄Cr(CO)₄; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Cr(0) is known in Cr(CO)₆; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Mn(–2) is known in Mn(cod)2−2; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Ram, R. S.; Bernath, P. F. (2003). "Fourier transform emission spectroscopy of the g⁴Δ–a⁴Δ system of FeCl". Journal of Molecular Spectroscopy. 221 (2): 261. Bibcode:2003JMoSp.221..261R. doi:10.1016/S0022-2852(03)00225-X.
Demazeau, G.; Buffat, B.; Pouchard, M.; Hagenmuller, P. (1982). "Recent developments in the field of high oxidation states of transition elements in oxides stabilization of six-coordinated Iron(V)". Zeitschrift für anorganische und allgemeine Chemie. 491: 60–66. doi:10.1002/zaac.19824910109.
Lu, J.; Jian, J.; Huang, W.; Lin, H.; Li, J; Zhou, M. (2016). "Experimental and theoretical identification of the Fe(VII) oxidation state in FeO₄⁻". Physical Chemistry Chemical Physics. 18 (45): 31125–31131. Bibcode:2016PCCP...1831125L. doi:10.1039/C6CP06753K. PMID 27812577.
Co(–3) is known in Na₃Co(CO)₃; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1117–1119. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Ni(–2) is known in Ni(COD)2−2; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Ni(0) is known in Ni(CO)₄; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Pfirrmann, Stefan; Limberg, Christian; Herwig, Christian; Stößer, Reinhard; Ziemer, Burkhard (2009). "A Dinuclear Nickel(I) Dinitrogen Complex and its Reduction in Single-Electron Steps". Angewandte Chemie International Edition. 48 (18): 3357–61. doi:10.1002/anie.200805862. PMID 19322853.
Carnes, Matthew; Buccella, Daniela; Chen, Judy Y.-C.; Ramirez, Arthur P.; Turro, Nicholas J.; Nuckolls, Colin; Steigerwald, Michael (2009). "A Stable Tetraalkyl Complex of Nickel(IV)". Angewandte Chemie International Edition. 48 (2): 290–4. doi:10.1002/anie.200804435. PMID 19021174.
Cu(−2) have been observed as dimeric anions [Cu₄]^2– in La₂Cu₂In; see Changhoon Lee; Myung-Hwan Whangbo (2008). "Late transition metal anions acting as p-metal elements". Solid State Sciences. 10 (4): 444–449. Bibcode:2008SSSci..10..444K. doi:10.1016/j.solidstatesciences.2007.12.001.
Jackson, Ross A.; Evans, Nicholas J.; Babula, Dawid J.; Horsley Downie, Thomas M.; Charman, Rex S. C.; Neale, Samuel E.; Mahon, Mary F.; Liptrot, David J. (2025-01-28). "Nucleophilicity at copper(-I) in a compound with a Cu–Mg bond". Nature Communications. 16 (1): 1101. Bibcode:2025NatCo..16.1101J. doi:10.1038/s41467-025-56544-z. ISSN 2041-1723. PMC 11775243. PMID 39875432.
Moret, Marc-Etienne; Zhang, Limei; Peters, Jonas C. (2013). "A Polar Copper–Boron One-Electron σ-Bond". J. Am. Chem. Soc. 135 (10): 3792–3795. Bibcode:2013JAChS.135.3792M. doi:10.1021/ja4006578. PMID 23418750.
Zn(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]²⁻, but later shown to be [T–T]⁴⁻ for all these elements) in Ca₅Zn₃ (structure (AE²⁺)₅(T–T)⁴⁻T²⁻⋅4e⁻); see Changhoon Lee; Myung-Hwan Whangbo (2008). "Late transition metal anions acting as p-metal elements". Solid State Sciences. 10 (4): 444–449. Bibcode:2008SSSci..10..444K. doi:10.1016/j.solidstatesciences.2007.12.001. and Changhoon Lee; Myung-Hwan Whangbo; Jürgen Köhler (2010). "Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T–T)^4– and Isolated T^2– Anions in the Polar Intermetallic Cr₅B₃-Type Compounds AE₅T₃ (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)". Zeitschrift für Anorganische und Allgemeine Chemie. 636 (1): 36–40. doi:10.1002/zaac.200900421.
Zn(0) has been observed; see Singh, Amit Pratap; Samuel, Prinson P.; Roesky, Herbert W.; Schwarzer, Martin C.; Frenking, Gernot; Sidhu, Navdeep S.; Dittrich, Birger (2013). "A Singlet Biradicaloid Zinc Compound and Its Nonradical Counterpart". J. Am. Chem. Soc. 135 (19): 7324–9. doi:10.1021/ja402351x. PMID 23600486. and Soleilhavoup, Michèle; Bertrand, Guy (2015). "Cyclic (Alkyl)(Amino)Carbenes (CAACs): Stable Carbenes on the Rise". Acc. Chem. Res. 48 (2): 256–266. doi:10.1021/ar5003494. PMID 25515548.
Zn(I) has been reported in decamethyldizincocene; see Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. (2004). "Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond". Science. 305 (5687): 1136–8. Bibcode:2004Sci...305.1136R. doi:10.1126/science.1101356. PMID 15326350. S2CID 38990338.
Hofmann, Patrick (1997). Colture. Ein Programm zur interaktiven Visualisierung von Festkörperstrukturen sowie Synthese, Struktur und Eigenschaften von binären und ternären Alkali- und Erdalkalimetallgalliden (PDF) (Thesis) (in German). PhD Thesis, ETH Zurich. p. 72. doi:10.3929/ethz-a-001859893. hdl:20.500.11850/143357. ISBN 978-3-7281-2597-2.
Ga(0) is known in gallium monoiodide; see Widdifield, Cory M.; Jurca, Titel; Richeson, Darrin S.; Bryce, David L. (2012-03-16). "Using 69/71Ga solid-state NMR and 127I NQR as probes to elucidate the composition of "GaI"". Polyhedron. 35 (1): 96–100. doi:10.1016/j.poly.2012.01.003. ISSN 0277-5387.
As(−1) has been observed in LiAs; see Reinhard Nesper (1990). "Structure and chemical bonding in zintl-phases containing lithium". Progress in Solid State Chemistry. 20 (1): 1–45. doi:10.1016/0079-6786(90)90006-2.
Abraham, Mariham Y.; Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Shaefer III, Henry F.; Schleyer, P. von R.; Robinson, Gregory H. (2010). "Carbene Stabilization of Diarsenic: From Hypervalency to Allotropy". Chemistry: A European Journal. 16 (2): 432–5. doi:10.1002/chem.200902840. PMID 19937872.
Ellis, Bobby D.; MacDonald, Charles L. B. (2004). "Stabilized Arsenic(I) Iodide: A Ready Source of Arsenic Iodide Fragments and a Useful Reagent for the Generation of Clusters". Inorganic Chemistry. 43 (19): 5981–6. doi:10.1021/ic049281s. PMID 15360247.
As(IV) has been observed in arsenic(IV) hydroxide (As(OH)₄) and HAsO⁻; see Kläning, Ulrik K.; Bielski, Benon H. J.; Sehested, K. (1989). "Arsenic(IV). A pulse-radiolysis study". Inorganic Chemistry. 28 (14): 2717–24. doi:10.1021/ic00313a007.
Se(−1) has been observed in diselenides(Se2−2, such as disodium diselenide (Na₂Se₂); see Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (2008). Lehrbuch der Anorganischen Chemie (in German) (102 ed.). Walter de Gruyter. p. 829. ISBN 978-3-11-020684-5. and H. Föppl; E. Busmann; F.-K. Frorath (1962). "Die Kristallstrukturen von α-Na2S2 und K2S2, β-Na2S2 und Na2Se2". Zeitschrift für anorganische und allgemeine Chemie (in German). 314 (1): 12–20. doi:10.1002/zaac.19623140104.
A Se(0) atom has been identified using DFT in [ReOSe(2-pySe)₃]; see Cargnelutti, Roberta; Lang, Ernesto S.; Piquini, Paulo; Abram, Ulrich (2014). "Synthesis and structure of [ReOSe(2-Se-py)3]: A rhenium(V) complex with selenium(0) as a ligand". Inorganic Chemistry Communications. 45: 48–50. doi:10.1016/j.inoche.2014.04.003. ISSN 1387-7003.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Se(III) has been observed in Se₂NBr₃; see Lau, Carsten; Neumüller, Bernhard; Vyboishchikov, Sergei F.; Frenking, Gernot; Dehnicke, Kurt; Hiller, Wolfgang; Herker, Martin (1996). "Se₂NBr₃, Se₂NCl₅, Se₂NCl⁻₆: New Nitride Halides of Selenium(III) and Selenium(IV)". Chemistry: A European Journal. 2 (11): 1393–1396. doi:10.1002/chem.19960021108.
Se(V) has been observed in SeO−3 and HSeO2−4; see Kläning, Ulrik K.; Sehested, K. (1986). "Selenium(V). A pulse radiolysis study". Inorganic Chemistry. 90 (21): 5460–4. doi:10.1021/j100412a112.
Rb(–1) is known in rubidides; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Colarusso, P.; Guo, B.; Zhang, K.-Q.; Bernath, P. F. (1996). "High-Resolution Infrared Emission Spectrum of Strontium Monofluoride" (PDF). J. Molecular Spectroscopy. 175 (1): 158. Bibcode:1996JMoSp.175..158C. doi:10.1006/jmsp.1996.0019.
Yttrium and all lanthanides except Ce and Pm have been observed in the oxidation state 0 in bis(1,3,5-tri-t-butylbenzene) complexes, see Cloke, F. Geoffrey N. (1993). "Zero Oxidation State Compounds of Scandium, Yttrium, and the Lanthanides". Chem. Soc. Rev. 22: 17–24. doi:10.1039/CS9932200017. and Arnold, Polly L.; Petrukhina, Marina A.; Bochenkov, Vladimir E.; Shabatina, Tatyana I.; Zagorskii, Vyacheslav V.; Cloke (2003-12-15). "Arene complexation of Sm, Eu, Tm and Yb atoms: a variable temperature spectroscopic investigation". Journal of Organometallic Chemistry. 688 (1–2): 49–55. doi:10.1016/j.jorganchem.2003.08.028.
Y(I) has been observed in gas-phase oxide clusters, see Kang, Weekyung; E. R. Bernstein (2005). "Formation of Yttrium Oxide Clusters Using Pulsed Laser Vaporization". Bull. Korean Chem. Soc. 26 (2): 345–348. doi:10.5012/bkcs.2005.26.2.345.
Zr(–2) is known in Zr(CO)2−6; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Zr(0) occur in (η⁶-(1,3,5-^tBu)₃C₆H₃)₂Zr and [(η⁵-C₅R₅Zr(CO)₄]⁻, see Chirik, P. J.; Bradley, C. A. (2007). "4.06 - Complexes of Zirconium and Hafnium in Oxidation States 0 to ii". Comprehensive Organometallic Chemistry III. From Fundamentals to Applications. Vol. 4. Elsevier Ltd. pp. 697–739. doi:10.1016/B0-08-045047-4/00062-5. ISBN 978-0-08-045047-6.
Calderazzo, Fausto; Pampaloni, Guido (January 1992). "Organometallics of groups 4 and 5: Oxidation states II and lower". Journal of Organometallic Chemistry. 423 (3): 307–328. doi:10.1016/0022-328X(92)83126-3.
Ma, Wen; Herbert, F. William; Senanayake, Sanjaya D.; Yildiz, Bilge (2015-03-09). "Non-equilibrium oxidation states of zirconium during early stages of metal oxidation". Applied Physics Letters. 106 (10). Bibcode:2015ApPhL.106j1603M. doi:10.1063/1.4914180. hdl:1721.1/104888. ISSN 0003-6951.
Nb(–3) occurs in Cs₃Nb(CO)_₅; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]₂⁻ to [Hf(CO)₆]₂⁻ and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.
Mo(–4) occurs in Na₄Mo(CO)_₄; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]^2– to [Hf(CO)₆]^2– and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.
Mo(0) occurs in molybdenum hexacarbonyl; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]^2– to [Hf(CO)₆]^2– and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.
Marcia F. Bailey; Lawrence F. Dahl (1965). "The Crystal Structure of Ditechnetium Decacarbonyl". Inorg. Chem. 4 (8): 1140–1145. doi:10.1021/ic50030a011.
Ru(–1) occurs in [Ru₂(CO)₈]^2–; see Xuenian Chen; Hima Kumar Lingam; Edward A. Meyers; Sheldon G. Shore (2012). "Structures of DMF solvated potassium and sodium salts of [Fe(CO)₄]^2– and [M₂(CO)₈]^2– (M = Fe, Ru)". Journal of Organometallic Chemistry. 721–722: 137–143. doi:10.1016/j.jorganchem.2012.07.040.
Ru(0) is present in the carbonyl-phosphine complex Ru(CO)₂(PPh₃)₃, see Stephane Sentets; Maria del Carmen Rodriguez Martinez; Laure Vendier; Bruno Donnadieu; Vincent Huc; Noël Lugan; Guy Lavigne (2005). "Instant "Base-Promoted" Generation of Roper's-type Ru(0) Complexes Ru(CO)₂(PR₃)₃ from a Simple Carbonylchlororuthenium(II) Precursor". J. Am. Chem. Soc. 127 (42): 14554–14555. doi:10.1021/ja055066e. PMID 16231891.
Rh(VII) is known in the RhO₃⁺ cation, see Da Silva Santos, Mayara; Stüker, Tony; Flach, Max; Ablyasova, Olesya S.; Timm, Martin; von Issendorff, Bernd; Hirsch, Konstantin; Zamudio-Bayer, Vicente; Riedel, Sebastian; Lau, J. Tobias (2022). "The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO3]+". Angew. Chem. Int. Ed. 61 (38) e202207688. doi:10.1002/anie.202207688. PMC 9544489. PMID 35818987.
Pd(I) is known in [Pd₂]²⁺ compounds; see Christoph Fricke; Theresa Sperger; Marvin Mendel; Franziska Schoenebeck (2020). "Catalysis with Palladium(I) Dimers". Angewandte Chemie International Edition. 60 (7): 3355–3366. doi:10.1002/anie.202011825. PMC 7898807. PMID 33058375.
Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on June 12, 2013.
Palladium(V) has been identified in complexes with organosilicon compounds containing pentacoordinate palladium; see Shimada, Shigeru; Li, Yong-Hua; Choe, Yoong-Kee; Tanaka, Masato; Bao, Ming; Uchimaru, Tadafumi (2007). "Multinuclear palladium compounds containing palladium centers ligated by five silicon atoms". Proceedings of the National Academy of Sciences. 104 (19): 7758–7763. Bibcode:2007PNAS..104.7758S. doi:10.1073/pnas.0700450104. PMC 1876520. PMID 17470819.
Ag(−2) have been observed as dimeric and monomeric anions in Ca₅Ag₃, (structure (Ca²⁺)₅(Ag–Ag)⁴⁻Ag²⁻⋅4e⁻); see Changhoon Lee; Myung-Hwan Whangbo; Jürgen Köhler (2010). "Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T–T)^4– and Isolated T^2– Anions in the Polar Intermetallic Cr₅B₃-Type Compounds AE₅T₃ (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)". Zeitschrift für Anorganische und Allgemeine Chemie. 636 (1): 36–40. doi:10.1002/zaac.200900421.
The Ag⁻ ion has been observed in metal ammonia solutions: see Tran, N. E.; Lagowski, J. J. (2001). "Metal Ammonia Solutions: Solutions Containing Argentide Ions". Inorganic Chemistry. 40 (5): 1067–68. doi:10.1021/ic000333x.
Ag(0) has been observed in carbonyl complexes in low-temperature matrices: see McIntosh, D.; Ozin, G. A. (1976). "Synthesis using metal vapors. Silver carbonyls. Matrix infrared, ultraviolet-visible, and electron spin resonance spectra, structures, and bonding of silver tricarbonyl, silver dicarbonyl, silver monocarbonyl, and disilver hexacarbonyl". J. Am. Chem. Soc. 98 (11): 3167–75. Bibcode:1976JAChS..98.3167M. doi:10.1021/ja00427a018.
Cd(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]²⁻, but later shown to be [T–T]⁴⁻) in Sr₅Cd₃; see Changhoon Lee; Myung-Hwan Whangbo; Jürgen Köhler (2010). "Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T–T)^4– and Isolated T^2– Anions in the Polar Intermetallic Cr₅B₃-Type Compounds AE₅T₃ (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)". Zeitschrift für Anorganische und Allgemeine Chemie. 636 (1): 36–40. doi:10.1002/zaac.200900421.
A cubic Cd₉⁸⁺ cluster with the central atom as Cd(0) has been identified in zeolite A; see Jennifer E. Readman; Peter D. Barker; Ian Gameson; Joe Hriljac; Wuzong Zhou; Peter Edwards; Paul Anderson (2004). "An ordered array of cadmium clusters assembled in zeolite A". Chemical communications (Cambridge, England). 10: 736–7. doi:10.1039/b400166d.
Guloy, A. M.; Corbett, J. D. (1996). "Synthesis, Structure, and Bonding of Two Lanthanum Indium Germanides with Novel Structures and Properties". Inorganic Chemistry. 35 (9): 2616–22. doi:10.1021/ic951378e. PMID 11666477.
Sn(−3) has been observed in [Sn₂]⁶⁻, e.g. in (Ba₂)⁴⁺(Mg₄)⁸⁺Sn⁴⁻(Sn₂)⁶⁻Sn²⁻ (with square (Sn²⁻)_n sheets), see Papoian, Garegin A.; Hoffmann, Roald (2000). "Hypervalent Bonding in One, Two, and Three Dimensions: Extending the Zintl–Klemm Concept to Nonclassical Electron-Rich Networks". Angew. Chem. Int. Ed. 2000 (39): 2408–2448. doi:10.1002/1521-3773(20000717)39:14<2408::aid-anie2408>3.0.co;2-u. PMID 10941096. Retrieved 2015-02-23.
Sb(−2) and Sb(−1) has been observed in [Sb₂]⁴⁻ and ¹_∞[Sb_n]ⁿ⁻, respectively; see Boss, Michael; Petri, Denis; Pickhard, Frank; Zönnchen, Peter; Röhr, Caroline (2005). "Neue Barium-Antimonid-Oxide mit den Zintl-Ionen [Sb]³⁻, [Sb₂]⁴⁻ und ¹_∞[Sb_n]ⁿ⁻ / New Barium Antimonide Oxides containing Zintl Ions [Sb]³⁻, [Sb₂]⁴⁻ and ¹_∞[Sb_n]ⁿ⁻". Zeitschrift für Anorganische und Allgemeine Chemie (in German). 631 (6–7): 1181–1190. doi:10.1002/zaac.200400546.
Anastas Sidiropoulos (2019). "Studies of N-heterocyclic Carbene (NHC) Complexes of the Main Group Elements". p. 39. doi:10.4225/03/5B0F4BDF98F60. S2CID 132399530.
Sb(I) has been observed in organoantimony compounds; see Šimon, Petr; de Proft, Frank; Jambor, Roman; Růžička, Aleš; Dostál, Libor (2010). "Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures". Angewandte Chemie International Edition. 49 (32): 5468–5471. doi:10.1002/anie.201002209. PMID 20602393.
Sb(+2) has been observed in distibines, see Patai, Saul, ed. (1994). The Chemistry of Organic Arsenic, Antimony, and Bismuth Compounds. Chemistry of Functional Groups. Chichester, UK: Wiley. p. 442. doi:10.1002/0470023473. ISBN 0-471-93044-X.
Sb(IV) has been observed in [SbCl₆]²⁻, see Nobuyoshi Shinohara; Masaaki Ohsima (2000). "Production of Sb(IV) Chloro Complex by Flash Photolysis of the Corresponding Sb(III) and Sb(V) Complexes in CH3CN and CHCl3". Bulletin of the Chemical Society of Japan. 73 (7): 1599–1604. doi:10.1246/bcsj.73.1599.
Te(−1) has been observed in BaTe₂, see Li, Jing; Guo, Hong You; Mulley, Suzanne; Proserpio, Davide M.; Sironi, Angelo (1994). "Synthesis and crystal structure of a new alkaline-earth metal chalcogenide: Barium ditelluride". Materials Research Bulletin. 29 (10): 1041–1048. doi:10.1016/0025-5408(94)90085-X. Retrieved 2025-11-18.
Te(III) has been observed in [Te(N(SiMe₃)₂)₂]⁺, see Heinze, Thorsten; Roesky, Herbert W.; Pauer, Frank; Stalke, Dietmar; Sheldrick, George M. (1991). "Synthesis and Structure of the First Tellurium(III) Radical Cation". Angewandte Chemie International Edition. 30 (12): 1678. doi:10.1002/anie.199116771. Retrieved 2015-02-23.
Te(V) is mentioned by Greenwood and Earnshaw, but they do not give any example of a Te(V) compound. What was long thought to be ditellurium decafluoride (Te₂F₁₀) is actually bis(pentafluorotelluryl) oxide, F₅TeOTeF₅: see Watkins, P. M. (1974). "Ditellurium decafluoride - A Continuing Myth". Journal of Chemical Education. 51 (9): 520–521. Bibcode:1974JChEd..51..520W. doi:10.1021/ed051p520. However, Te(V) has been observed in HTeO⁻, TeO⁻, HTeO−2, and TeO−3; see Kläning, Ulrik K.; Sehested, K. (2001). "Tellurium(V). A Pulse Radiolysis Study". The Journal of Physical Chemistry A. 105 (27): 6637–45. Bibcode:2001JPCA..105.6637K. doi:10.1021/jp010577i.
I(II) is known to exist in monoxide (IO); see Nikitin, I V (31 August 2008). "Halogen monoxides". Russian Chemical Reviews. 77 (8): 739–749. Bibcode:2008RuCRv..77..739N. doi:10.1070/RC2008v077n08ABEH003788. S2CID 250898175.
I(VI) has been observed in IO₃, IO₄²⁻, H₅IO₆⁻, H₂IO₅²⁻, H₄IO₆²⁻, and HIO₅³⁻; see Kläning, Ulrik K.; Sehested, Knud; Wolff, Thomas (1981). "Laser flash photolysis and pulse radiolysis of iodate and periodate in aqueous solution. Properties of iodine(VI)". J. Chem. Soc., Faraday Trans. 1. 77 (7): 1707–18. doi:10.1039/F19817701707.
Dye, J. L. (1979). "Compounds of Alkali Metal Anions". Angewandte Chemie International Edition. 18 (8): 587–598. doi:10.1002/anie.197905871.
Xu, Wei; Lerner, Michael M. (2018). "A New and Facile Route Using Electride Solutions to Intercalate Alkaline Earth Ions into Graphite". Chemistry of Materials. 30 (19): 6930–6935. doi:10.1021/acs.chemmater.8b03421. S2CID 105295721.
La(I), Pr(I), Tb(I), Tm(I), and Yb(I) have been observed in MB₈⁻ clusters; see Li, Wan-Lu; Chen, Teng-Teng; Chen, Wei-Jia; Li, Jun; Wang, Lai-Sheng (2021). "Monovalent lanthanide(I) in borozene complexes". Nature Communications. 12 (1): 6467. Bibcode:2021NatCo..12.6467L. doi:10.1038/s41467-021-26785-9. PMC 8578558. PMID 34753931.
Chen, Xin; et al. (2019-12-13). "Lanthanides with Unusually Low Oxidation States in the PrB₃^– and PrB₄^– Boride Clusters". Inorganic Chemistry. 58 (1): 411–418. doi:10.1021/acs.inorgchem.8b02572. PMID 30543295. S2CID 56148031.
All the lanthanides, except Pm, in the +2 oxidation state have been observed in organometallic molecular complexes, see Lanthanides Topple Assumptions and Meyer, G. (2014). "All the Lanthanides Do It and Even Uranium Does Oxidation State +2". Angewandte Chemie International Edition. 53 (14): 3550–51. doi:10.1002/anie.201311325. PMID 24616202.. Additionally, all the lanthanides (La–Lu) form dihydrides (LnH₂), dicarbides (LnC₂), monosulfides (LnS), monoselenides (LnSe), and monotellurides (LnTe), but for most elements these compounds have Ln³⁺ ions with electrons delocalized into conduction bands, e. g. Ln³⁺(H⁻)₂(e⁻).
Boggiano, Andrew C.; Studvick, Chad M.; Roy Chowdhury, Sabyasachi; Niklas, Julie E.; Tateyama, Haruko; Wu, Hongwei; Leisen, Johannes E.; Kleemiss, Florian; Vlaisavljevich, Bess; Popov, Ivan A.; La Pierre, Henry S. (July 2025). "Praseodymium in the formal +5 oxidation state". Nature Chemistry. 17 (7): 1005–1010. doi:10.1038/s41557-025-01797-w. ISSN 1755-4349.
SmB₆⁻ cluster anion has been reported and contains Sm in rare oxidation state of +1; see Paul, J. Robinson; Xinxing, Zhang; Tyrel, McQueen; Kit, H. Bowen; Anastassia, N. Alexandrova (2017). "SmB₆^– Cluster Anion: Covalency Involving f Orbitals". J. Phys. Chem. A. 121 (8): 1849–1854. Bibcode:2017JPCA..121.1849R. doi:10.1021/acs.jpca.7b00247. PMID 28182423. S2CID 3723987..
Hf(–2) occurs in Hf(CO)_₆²⁻; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]₂⁻ to [Hf(CO)₆]₂⁻ and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.
Hf(0) occur in (η⁶-(1,3,5-^tBu)₃C₆H₃)₂Hf and [(η⁵-C₅R₅Hf(CO)₄]⁻, see Chirik, P. J.; Bradley, C. A. (2007). "4.06 - Complexes of Zirconium and Hafnium in Oxidation States 0 to ii". Comprehensive Organometallic Chemistry III. From Fundamentals to Applications. Vol. 4. Elsevier Ltd. pp. 697–739. doi:10.1016/B0-08-045047-4/00062-5. ISBN 978-0-08-045047-6.
Ta(–3) occurs in Ta(CO)_₅³⁻; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]₂⁻ to [Hf(CO)₆]₂⁻ and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.
Ta(0) is known in Ta(CNDipp)₆; see Khetpakorn Chakarawet; Zachary W. Davis-Gilbert; Stephanie R. Harstad; Victor G. Young Jr.; Jeffrey R. Long; John E. Ellis (2017). "Ta(CNDipp)6: An Isocyanide Analogue of Hexacarbonyltantalum(0)". Angewandte Chemie International Edition. 56 (35): 10577–10581. doi:10.1002/anie.201706323. PMID 28697283. Additionally, Ta(0) has also been previously reported in Ta(bipy)₃, but this has been proven to contain Ta(V).
W(−4) is known in W(CO)4−4; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
W(0) is known in W(CO)₆; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Re(0) is known in Re₂(CO)₁₀; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–3186. doi:10.1021/ic052110i.
Os(–1) occurs in [Os₂(CO)₈]^2–; see Leh Yeh Hsu; Nripendra Bhattacharyya; Sheldon G. Shore (1985). "Binuclear carbonylates [Ru₂(CO)₈]^2– and [Os₂(CO)₈]^2–: syntheses and crystal structures". Organometallics. 4 (8): 1483–1485. doi:10.1021/om00127a041.
Os(0) is known in Os(CO)₅; see Rushman, Paul; Van Buuren, Gilbert N.; Shiralian, Mahmoud; Pomeroy, Roland K. (1983). "Properties of the Pentacarbonyls of Ruthenium and Osmium". Organometallics. 2 (5): 693–694. doi:10.1021/om00077a026.
Ir(−3) has been observed in Ir(CO)₃³⁻; see Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1117. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Ir(–2) has been observed in IrVO₂^–; see Le-Shi Chen; Yun-Zhu Liu; Jiao-Jiao Chen; Si-Dun Wang; Tong-Mei Ma; Xiao-Na Li; Sheng-Gui He (2022). "Water–Gas Shift Catalyzed by Iridium–Vanadium Oxide Clusters IrVO₂^– with Iridium in a Rare Oxidation State of −II". The Journal of Physical Chemistry A. 126 (32): 5294–5301. doi:10.1021/acs.jpca.2c03974.
Pergola, R. D.; Garlaschelli, L.; Matinengo, S. (1990). Dodecacarbonyltetrairidium: Ir₄(CO)₁₂. Inorganic Syntheses. Vol. 28. pp. 245–247. doi:10.1002/9780470132593.ch63. ISBN 9780470132593.
Ir(VIII) has been observed in iridium tetroxide (IrO₄); see Gong, Yu; Zhou, Mingfei; Kaupp, Martin; Riedel, Sebastian (2009). "Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII". Angewandte Chemie International Edition. 48 (42): 7879–7883. doi:10.1002/anie.200902733. PMID 19593837.
Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Pt(−2) has been observed in Cs₂Pt, see Karpov, Andrey; Nuss, Jürgen; Wedig, Ulrich; Jansen, Martin (2003-10-13). "Cs2Pt: A Platinide(-II) Exhibiting Complete Charge Separation". Angewandte Chemie International Edition. 42 (39). Wiley: 4818–4821. doi:10.1002/anie.200352314. ISSN 1433-7851..
Pt(0) has been observed in organoplatinum compounds, e. g. (PPh₃)₂PtC₂H₄; see Cheng, P.-T.; Nyburg, S. C. (1972). "The Crystal and Molecular Structure of bis(triphenylphosphine)-(ethylene)platinum, (PPh₃)₂PtC₂H₄". Canadian Journal of Chemistry. 50 (6): 912–916. doi:10.1139/v72-142.
Pt(I) has been observed in [Pt₂(CO)₆]²⁺; see Xu, Qiang; Heaton, Brian T.; Jacob, Chacko; Mogi, Koichi; Ichihashi, Yuichi; Souma, Yoshie; Kanamori, Kan; Eguchi, Taro (2000). "Hexacarbonyldiplatinum(I). Synthesis, spectroscopy, and density functional calculation of the first homoleptic, dinuclear platinum(I) carbonyl cation, [{Pt(CO)₃}₂]²⁺, formed in concentrated sulfuric acid". Journal of the American Chemical Society. 122 (29): 6862–6870. doi:10.1021/ja000716u.
Pt(III) has been observed; see O'Halloran, Thomas V.; Lippard, Stephen J. (1985). "The Chemistry of Platinum in the +3 Oxidation State". Israel Journal of Chemistry. 25 (2): 130–137. doi:10.1002/ijch.198500021.
Mézaille, Nicolas; Avarvari, Narcis; Maigrot, Nicole; Ricard, Louis; Mathey, François; Le Floch, Pascal; Cataldo, Laurent; Berclaz, Théo; Geoffroy, Michel (1999). "Gold(I) and Gold(0) Complexes of Phosphinine-Based Macrocycles". Angewandte Chemie International Edition. 38 (21): 3194–3197. doi:10.1002/(SICI)1521-3773(19991102)38:21<3194::AID-ANIE3194>3.0.CO;2-O. PMID 10556900.
Brauer, G.; Haucke, W. (1936-06-01). "Kristallstruktur der intermetallischen Phasen MgAu und MgHg". Zeitschrift für Physikalische Chemie. 33B (1): 304–310. doi:10.1515/zpch-1936-3327. ISSN 2196-7156. MgHg then lends itself to an oxidation state of +2 for Mg and -2 for Hg because it consists entirely of these polar bonds with no evidence of electron unpairing. (translated)
Dong, Z.-C.; Corbett, J. D. (1996). "Na₂₃K₉Tl_15.3: An Unusual Zintl Compound Containing Apparent Tl₅⁷⁻, Tl₄⁸⁻, Tl₃⁷⁻, and Tl⁵⁻ Anions". Inorganic Chemistry. 35 (11): 3107–12. doi:10.1021/ic960014z. PMID 11666505.
Tl(−2) has been observed in Na₂Tl; see Sangster, James (February 2018). "The Systems Li-Tl, Na-Tl and K-Tl". Journal of Phase Equilibria and Diffusion. 39 (1): 74–86. doi:10.1007/s11669-017-0609-9. ISSN 1547-7037.
Tl(−1) has been observed in NaTl; see Sangster, James (February 2018). "The Systems Li-Tl, Na-Tl and K-Tl". Journal of Phase Equilibria and Diffusion. 39 (1): 74–86. doi:10.1007/s11669-017-0609-9. ISSN 1547-7037.
Tl(+2) has been observed in tetrakis(hypersilyl)dithallium ([(Me₃Si)Si]₂Tl—Tl[Si(SiMe₃)]₂), see Sonja Henkel; Dr. Karl Wilhelm Klinkhammer; Dr. Wolfgang Schwarz (1994). "Tetrakis(hypersilyl)dithallium(Tl—Tl): A Divalent Thallium Compound". Angew. Chem. Int. Ed. 33 (6): 681–683. doi:10.1002/anie.199406811.
Pb(−2) has been observed in BaPb, see Ferro, Riccardo (2008). Nicholas C. Norman (ed.). Intermetallic Chemistry. Elsevier. p. 505. ISBN 978-0-08-044099-6. and Todorov, Iliya; Sevov, Slavi C. (2004). "Heavy-Metal Aromatic Rings: Cyclopentadienyl Anion Analogues Sn₅⁶⁻ and Pb₅⁶⁻ in the Zintl Phases Na₈BaPb₆, Na₈BaSn₆, and Na₈EuSn₆". Inorganic Chemistry. 43 (20): 6490–94. doi:10.1021/ic000333x.
Pb(−1) has been observed in CsPb, see Hewaidy, I. F.; Busmann, E.; Klemm, W. (1964). "Die Struktur der AB-Verbindungen der schweren Alkalimetalle mit Zinn und Blei". Zeitschrift für anorganische und allgemeine Chemie (in German). 328 (5–6): 283–293. doi:10.1002/zaac.19643280511.
Pb(0) carbonyls have been observed in reaction between lead atoms and carbon monoxide; see Ling, Jiang; Qiang, Xu (2005). "Observation of the lead carbonyls Pb_nCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon". The Journal of Chemical Physics. 122 (3): 034505. 122 (3): 34505. Bibcode:2005JChPh.122c4505J. doi:10.1063/1.1834915. ISSN 0021-9606. PMID 15740207. Also, Pb(0) has been observed in [Si^II(Xant)Si^II]PbFe(CO)₄; see Jian Xu; Sudip Pan; Shenglai Yao; Gernot Frenking; Matthias Driess (2022). "The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex ("Plumbylone")". Angewandte Chemie International Edition. 61 (38): e202209442. doi:10.1002/anie.202209442. PMC 9545849. PMID 35848899.{{cite journal}}: CS1 maint: article number as page number (link)
Siew-Peng Chia; Hong-Wei Xi; Yongxin Li; Kok Hwa Lim; Cheuk-Wai So (2013). "A Base-Stabilized Lead(I) Dimer and an Aromatic Plumbylidenide Anion". Angew. Chem. Int. Ed. 52 (24): 6298–6301. doi:10.1002/anie.201301954. PMID 23629949.
Becker, M.; Förster, C.; Franzen, C.; et al. (2008). "Persistent radicals of trivalent tin and lead". Inorganic Chemistry. 47 (21): 9965–78. doi:10.1021/ic801198p. PMID 18823115.
Mosseri, S.; Henglein, A.; Janata, E. (1990). "Trivalent lead as an intermediate in the oxidation of lead(II) and the reduction of lead(IV) species". Journal of Physical Chemistry. 94 (6): 2722–26. Bibcode:1990JPhCh..94.2722M. doi:10.1021/j100369a089.
Bi(I) has been observed in organobismuth compounds; see Šimon, Petr; de Proft, Frank; Jambor, Roman; Růžička, Aleš; Dostál, Libor (2010). "Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures". Angewandte Chemie International Edition. 49 (32): 5468–5471. doi:10.1002/anie.201002209. PMID 20602393.
Bi(+2) has been observed in dibismuthines (R₂Bi—BiR₂), see Ashe, Arthur J. III (1990). "Thermochromic Distibines and Dibismuthines". Advances in Organometallic Chemistry. 30: 77–97. doi:10.1016/S0065-3055(08)60499-2. ISBN 9780120311309.
Bi(IV) has been observed; see A. I. Aleksandrov, I. E. Makarov (1987). "Formation of Bi(II) and Bi(IV) in aqueous hydrochloric solutions of Bi(III)". Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science. 36 (2): 217–220. doi:10.1007/BF00959349. S2CID 94865394.
Thayer, John S. (2010). "Relativistic Effects and the Chemistry of the Heavier Main Group Elements". Relativistic Methods for Chemists. Challenges and Advances in Computational Chemistry and Physics. Vol. 10. p. 78. doi:10.1007/978-1-4020-9975-5_2. ISBN 978-1-4020-9974-8.
Pore, Jennifer L.; Gates, Jacklyn M.; Dixon, David A.; Garcia, Fatima H.; Gibson, John K.; Gooding, John A.; McCarthy, Mallory; Orford, Rodney; Shafi, Ziad; Shuh, David K.; Sprouse, Sarah (2025). "Direct identification of Ac and No molecules with an atom-at-a-time technique". Nature. 644. Springer Science and Business Media LLC: 376–380. doi:10.1038/s41586-025-09342-y. ISSN 0028-0836.
Th(-I) and U(-I) have been detected in the gas phase as octacarbonyl anions; see Chaoxian, Chi; Sudip, Pan; Jiaye, Jin; Luyan, Meng; Mingbiao, Luo; Lili, Zhao; Mingfei, Zhou; Gernot, Frenking (2019). "Octacarbonyl Ion Complexes of Actinides [An(CO)₈]^+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding". Chemistry (Weinheim an der Bergstrasse, Germany). 25 (50): 11772–11784. 25 (50): 11772–11784. doi:10.1002/chem.201902625. ISSN 0947-6539. PMC 6772027. PMID 31276242.
Th(I) is known in thorium(I) bromide (ThBr); see Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. (2006). "Thorium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 52–160. doi:10.1007/1-4020-3598-5_3. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 2016-03-07.
Pa(II) is known in protactinium monoxide (PaO); see Sellers, Philip A.; Fried, Sherman; Elson, Robert E.; Zachariasen, W. H. (1954). "The Preparation of Some Protactinium Compounds and the Metal". Journal of the American Chemical Society. 76 (23): 5935. Bibcode:1954JAChS..76.5935S. doi:10.1021/ja01652a011.
U(I) has been observed in [U(η⁵-C₅ⁱPr₅)₂]⁻, see Barluzzi, Luciano; Giblin, Sean R.; Mansikkamäki, Akseli; Layfield, Richard A. (2022). "Identification of Oxidation State +1 in a Molecular Uranium Complex". J. Am. Chem. Soc. 144 (40): 18229–18233. doi:10.1021/jacs.2c06519. PMID 36169550. S2CID 252567088. Retrieved 13 July 2023.
U(II) has been observed in [K(2.2.2-Cryptand)][(C₅H₄SiMe₃)₃U], see MacDonald, Matthew R.; Fieser, Megan E.; Bates, Jefferson E.; Ziller, Joseph W.; Furche, Filipp; Evans, William J. (2013). "Identification of the +2 Oxidation State for Uranium in a Crystalline Molecular Complex, [K(2.2.2-Cryptand)][(C₅H₄SiMe₃)₃U]". J. Am. Chem. Soc. 135 (36): 13310–13313. doi:10.1021/ja406791t. PMID 23984753.
Np(II), (III) and (IV) have been observed, see Dutkiewicz, Michał S.; Apostolidis, Christos; Walter, Olaf; Arnold, Polly L (2017). "Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding". Chem. Sci. 8 (4): 2553–2561. doi:10.1039/C7SC00034K. PMC 5431675. PMID 28553487.
Windorff, Cory J.; Chen, Guo P; Cross, Justin N; Evans, William J.; Furche, Filipp; Gaunt, Andrew J.; Janicke, Michael T.; Kozimor, Stosh A.; Scott, Brian L. (2017). "Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of {Pu^II[C₅H₃(SiMe₃)₂]₃}⁻". J. Am. Chem. Soc. 139 (11): 3970–3973. doi:10.1021/jacs.7b00706. PMID 28235179.
Preparation of plutonium(VIII) compounds has been claimed, see Zaitsevskii, Andréi; Mosyagin, Nikolai S.; Titov, Anatoly V.; Kiselev, Yuri M. (July 21, 2013). "Relativistic density functional theory modeling of plutonium and americium higher oxide molecules". The Journal of Chemical Physics. 139 (3) 034307. Bibcode:2013JChPh.139c4307Z. doi:10.1063/1.4813284. PMID 23883027. and Kiselev, Yu. M.; Nikonov, M. V.; Dolzhenko, V. D.; Ermilov, A. Yu.; Tananaev, I. G.; Myasoedov, B. F. (January 17, 2014). "On existence and properties of plutonium(VIII) derivatives". Radiochimica Acta. 102 (3): 227–237. doi:10.1515/ract-2014-2146. S2CID 100915090. But their existence has been partially disproven, see Fedosseev, Alexander M.; Bessonov, Alexi A.; Shilov, Vladimir P. (September 5, 2022). "Is octavalent plutonium really formed during oxidation in alkaline aqueous solutions?". Radiochimica Acta. 110 (12): 955–959. doi:10.1515/ract-2022-0056.
Am(VII) has been observed in AmO3−5; see Americium, Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010 and Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1265. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Cm(II) has been observed in chloride melts, see Mikheev, Nikolai B.; Auerman, L. N.; Rumer, Igor A.; Kamenskaya, Alla N.; Kazakevich, M. Z. (1992). "The anomalous stabilisation of the oxidation state 2+ of lanthanides and actinides". Russian Chemical Reviews. 61 (10): 990–998. Bibcode:1992RuCRv..61..990M. doi:10.1070/RC1992v061n10ABEH001011. S2CID 250859394.
Kovács, Attila; Dau, Phuong D.; Marçalo, Joaquim; Gibson, John K. (2018). "Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States". Inorg. Chem. 57 (15). American Chemical Society: 9453–9467. doi:10.1021/acs.inorgchem.8b01450. OSTI 1631597. PMID 30040397. S2CID 51717837.
Domanov, V. P.; Lobanov, Yu. V. (October 2011). "Formation of volatile curium(VI) trioxide CmO₃". Radiochemistry. 53 (5). SP MAIK Nauka/Interperiodica: 453–6. Bibcode:2011Radch..53..453D. doi:10.1134/S1066362211050018. S2CID 98052484.
Sullivan, Jim C.; Schmidt, K. H.; Morss, L. R.; Pippin, C. G.; Williams, C. (1988). "Pulse radiolysis studies of berkelium(III): preparation and identification of berkelium(II) in aqueous perchlorate media". Inorganic Chemistry. 27 (4): 597. doi:10.1021/ic00277a005.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1265. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Es(IV) is known in einsteinium(IV) fluoride (EsF₄); see Kleinschmidt, P. (1994). "Thermochemistry of the actinides". Journal of Alloys and Compounds. 213–214: 169–172. doi:10.1016/0925-8388(94)90898-2.
Sg(0) has been observed in seaborgium hexacarbonyl (Sg(CO)₆); see Even, J.; Yakushev, A.; Dullmann, C. E.; Haba, H.; et al. (2014). "Synthesis and detection of a seaborgium carbonyl complex". Science. 345 (6203): 1491–3. Bibcode:2014Sci...345.1491E. doi:10.1126/science.1255720. PMID 25237098. S2CID 206558746.
Sg(VI) has been observed in seaborgium oxide hydroxide (SgO₂(OH)₂); see Huebener, S.; Taut, S.; Vahle, A.; Dressler, R.; et al. (2001). "Physico-chemical characterization of seaborgium as oxide hydroxide" (PDF). Radiochim. Acta. 89 (11–12): 737–741. doi:10.1524/ract.2001.89.11-12.737. S2CID 98583998. Archived from the original (PDF) on 2014-10-25.
Langmuir, Irving (1919). "The arrangement of electrons in atoms and molecules". J. Am. Chem. Soc. 41 (6): 868–934. Bibcode:1919JAChS..41..868L. doi:10.1021/ja02227a002. Archived from the original on 2019-06-21. Retrieved 2019-07-01.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 33. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
Jensen, W. B. (2007). "the origin of the oxidation-state concept". J. Chem. Educ. 84 (9): 1418–1419. Bibcode:2007JChEd..84.1418J. doi:10.1021/ed084p1418.
Stock, A. (1919). "Einige Nomenklaturfragen der anorganischen Chemie" [Some nomenclature issues of inorganic chemistry]. Angew. Chem. 32 (98): 373–374. Bibcode:1919AngCh..32..373S. doi:10.1002/ange.19190329802. Archived from the original on 2020-08-06. Retrieved 2019-07-01.
Jorissen, W. P.; Bassett, H.; Damiens, A.; Fichter, F.; Rémy, H. (1941). "Rules for naming inorganic compounds". J. Am. Chem. Soc. 63: 889–897. doi:10.1021/ja01849a001.
Bray, W. C.; Branch, G. E. K. (1913). "Valence and tautomerism". J. Am. Chem. Soc. 35 (10): 1440–1447. Bibcode:1913JAChS..35.1440B. doi:10.1021/ja02199a003. Archived from the original on 2021-02-09. Retrieved 2019-09-16.
Noyes, A. A.; Pitzer, K. S.; Dunn, C. L. (1935). "Argentic salts in acid solution, I. The oxidation and reduction reactions". J. Am. Chem. Soc. 57 (7): 1221–1229. Bibcode:1935JAChS..57.1221N. doi:10.1021/ja01310a018.
Noyes, A. A.; Pitzer, K. S.; Dunn, C. L. (1935). "Argentic salts in acid solution, II. The oxidation state of argentic salts". J. Am. Chem. Soc. 57 (7): 1229–1237. Bibcode:1935JAChS..57.1229N. doi:10.1021/ja01310a019.
Fernelius, W. C. (1948). "Some problems of inorganic nomenclature". Chem. Eng. News. 26: 161–163. doi:10.1021/cen-v026n003.p161.
Fernelius, W. C.; Larsen, E. M.; Marchi, L. E.; Rollinson, C. L. (1948). "Nomenclature of coördination compounds". Chem. Eng. News. 26 (8): 520–523. doi:10.1021/cen-v026n008.p520.
Pauling, L. (1948). "The modern theory of valency". J. Chem. Soc. 1948: 1461–1467. doi:10.1039/JR9480001461. PMID 18893624. Archived from the original on 2021-12-07. Retrieved 2021-11-22.
Calvert, J. G. (1990). "IUPAC Recommendation 1990". Pure Appl. Chem. 62: 2204. doi:10.1351/pac199062112167.

dtu.dk (Global: low place; English: 8,755^th place)

orbit.dtu.dk

Se(V) has been observed in SeO−3 and HSeO2−4; see Kläning, Ulrik K.; Sehested, K. (1986). "Selenium(V). A pulse radiolysis study". Inorganic Chemistry. 90 (21): 5460–4. doi:10.1021/j100412a112.
Te(V) is mentioned by Greenwood and Earnshaw, but they do not give any example of a Te(V) compound. What was long thought to be ditellurium decafluoride (Te₂F₁₀) is actually bis(pentafluorotelluryl) oxide, F₅TeOTeF₅: see Watkins, P. M. (1974). "Ditellurium decafluoride - A Continuing Myth". Journal of Chemical Education. 51 (9): 520–521. Bibcode:1974JChEd..51..520W. doi:10.1021/ed051p520. However, Te(V) has been observed in HTeO⁻, TeO⁻, HTeO−2, and TeO−3; see Kläning, Ulrik K.; Sehested, K. (2001). "Tellurium(V). A Pulse Radiolysis Study". The Journal of Physical Chemistry A. 105 (27): 6637–45. Bibcode:2001JPCA..105.6637K. doi:10.1021/jp010577i.

ed.ac.uk (Global: 1,871^st place; English: 1,234^th place)

pure.ed.ac.uk

Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.

elsevier.com (Global: 610^th place; English: 704^th place)

linkinghub.elsevier.com

Calderazzo, Fausto; Pampaloni, Guido (January 1992). "Organometallics of groups 4 and 5: Oxidation states II and lower". Journal of Organometallic Chemistry. 423 (3): 307–328. doi:10.1016/0022-328X(92)83126-3.

escholarship.org (Global: 1,523^rd place; English: 976^th place)

Kovács, Attila; Dau, Phuong D.; Marçalo, Joaquim; Gibson, John K. (2018). "Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States". Inorg. Chem. 57 (15). American Chemical Society: 9453–9467. doi:10.1021/acs.inorgchem.8b01450. OSTI 1631597. PMID 30040397. S2CID 51717837.

ghostarchive.org (Global: 32^nd place; English: 21^st place)

Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.
Connelly, N. G.; Damhus, T.; Hartshorn, R. M.; Hutton, A. T. Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005) (PDF). RSC Publishing. Archived (PDF) from the original on 2022-10-09.

gsi.de (Global: low place; English: low place)

gsi.de

Bh(VII) has been observed in bohrium oxychloride (BhO₃Cl); see Eichler R, Düllmann C, Gäggeler HW, Eichler B, et al. "Gas chemical investigation of bohrium (Bh, element 107)" (PDF). GSI Annual Report 2000. Archived from the original (PDF) on 2008-02-28. Retrieved 2008-02-29.
Hs(VIII) has been observed in hassium tetroxide (HsO₄); see "Chemistry of Hassium" (PDF). Gesellschaft für Schwerionenforschung mbH. 2002. Retrieved 2007-01-31.

www-w2k.gsi.de

Sg(VI) has been observed in seaborgium oxide hydroxide (SgO₂(OH)₂); see Huebener, S.; Taut, S.; Vahle, A.; Dressler, R.; et al. (2001). "Physico-chemical characterization of seaborgium as oxide hydroxide" (PDF). Radiochim. Acta. 89 (11–12): 737–741. doi:10.1524/ract.2001.89.11-12.737. S2CID 98583998. Archived from the original (PDF) on 2014-10-25.

handle.net (Global: 102^nd place; English: 76^th place)

hdl.handle.net

Karen, P.; McArdle, P.; Takats, J. (2016). "Comprehensive definition of oxidation state (IUPAC Recommendations 2016)". Pure Appl. Chem. 88 (8): 831–839. doi:10.1515/pac-2015-1204. hdl:10852/59520. S2CID 99403810.
Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.
Hofmann, Patrick (1997). Colture. Ein Programm zur interaktiven Visualisierung von Festkörperstrukturen sowie Synthese, Struktur und Eigenschaften von binären und ternären Alkali- und Erdalkalimetallgalliden (PDF) (Thesis) (in German). PhD Thesis, ETH Zurich. p. 72. doi:10.3929/ethz-a-001859893. hdl:20.500.11850/143357. ISBN 978-3-7281-2597-2.
Ma, Wen; Herbert, F. William; Senanayake, Sanjaya D.; Yildiz, Bilge (2015-03-09). "Non-equilibrium oxidation states of zirconium during early stages of metal oxidation". Applied Physics Letters. 106 (10). Bibcode:2015ApPhL.106j1603M. doi:10.1063/1.4914180. hdl:1721.1/104888. ISSN 0003-6951.

harvard.edu (Global: 18^th place; English: 17^th place)

ui.adsabs.harvard.edu

Wang, G.; Zhou, M.; Goettel, G. T.; Schrobilgen, G. J.; Su, J.; Li, J.; Schlöder, T.; Riedel, S. (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Hooydonk, G. Van (1974-05-01). "O n an Ionic Approximation to Chemical Bonding". Zeitschrift für Naturforschung A. 29 (5): 763–767. Bibcode:1974ZNatA..29..763H. doi:10.1515/zna-1974-0517. ISSN 1865-7109.
Martinie, R. J.; Bultema, J. J.; Wal, M. N. V.; Burkhart, B. J.; Griend, D. A. V.; DeCock, R. L. (2011). "Bond order and chemical properties of BF, CO, and N₂". J. Chem. Educ. 88 (8): 1094–1097. Bibcode:2011JChEd..88.1094M. doi:10.1021/ed100758t.
Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.
Li(–1) has been observed in the gas phase; see R. H. Sloane; H. M. Love (1947). "Surface Formation of Lithium Negative Ions". Nature. 159 (4035): 302–303. Bibcode:1947Natur.159..302S. doi:10.1038/159302a0.
Boronski, Josef T.; Crumpton, Agamemnon E.; Wales, Lewis L.; Aldridge, Simon (2023-06-16). "Diberyllocene, a stable compound of Be(I) with a Be–Be bond". Science. 380 (6650): 1147–1149. Bibcode:2023Sci...380.1147B. doi:10.1126/science.adh4419. ISSN 0036-8075. PMID 37319227. S2CID 259166086.
Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A. (2012). "Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond". Science. 336 (6087): 1420–2. Bibcode:2012Sci...336.1420B. doi:10.1126/science.1221138. PMID 22700924. S2CID 206540959.
Zhang, K.Q.; Guo, B.; Braun, V.; Dulick, M.; Bernath, P.F. (1995). "Infrared Emission Spectroscopy of BF and AIF" (PDF). J. Molecular Spectroscopy. 170 (1): 82. Bibcode:1995JMoSp.170...82Z. doi:10.1006/jmsp.1995.1058.
Tetrazoles contain a pair of double-bonded nitrogen atoms with oxidation state 0 in the ring. A Synthesis of the parent 1H-tetrazole, CH₂N₄ (two atoms N(0)) is given in Henry, Ronald A.; Finnegan, William G. (1954). "An Improved Procedure for the Deamination of 5-Aminotetrazole". Journal of the American Chemical Society. 76 (1): 290–291. Bibcode:1954JAChS..76..290H. doi:10.1021/ja01630a086. ISSN 0002-7863.
Ne(0) has been observed in Cr(CO)₅Ne; see Perutz, Robin N.; Turner, James J. (August 1975). "Photochemistry of the Group 6 hexacarbonyls in low-temperature matrices. III. Interaction of the pentacarbonyls with noble gases and other matrices". Journal of the American Chemical Society. 97 (17): 4791–4800. Bibcode:1975JAChS..97.4791P. doi:10.1021/ja00850a001.
Mg(0) has been synthesized in a compound containing a Na₂Mg₂²⁺ cluster coordinated to a bulky organic ligand; see Rösch, B.; Gentner, T. X.; Eyselein, J.; Langer, J.; Elsen, H.; Li, W.; Harder, S. (2021). "Strongly reducing magnesium(0) complexes". Nature. 592 (7856): 717–721. Bibcode:2021Natur.592..717R. doi:10.1038/s41586-021-03401-w. PMID 33911274. S2CID 233447380
Bernath, P. F.; Black, J. H. & Brault, J. W. (1985). "The spectrum of magnesium hydride" (PDF). Astrophysical Journal. 298: 375. Bibcode:1985ApJ...298..375B. doi:10.1086/163620.. See also Low valent magnesium compounds.
Al(–1) has been reported in Na₅Al₅; see Haopeng Wang; Xinxing Zhang; Yeon Jae Ko; Andrej Grubisic; Xiang Li; Gerd Ganteför; Hansgeorg Schnöckel; Bryan W. Eichhorn; Mal-Soon Lee; P. Jena; Anil K. Kandalam; Boggavarapu Kiran; Kit H. Bowen (2014). "Aluminum Zintl anion moieties within sodium aluminum clusters". The Journal of Chemical Physics. 140 (5). Bibcode:2014JChPh.140e4301W. doi:10.1063/1.4862989.
Unstable carbonyl of Al(0) has been detected in reaction of Al₂(CH₃)₆ with carbon monoxide; see Sanchez, Ramiro; Arrington, Caleb; Arrington Jr., C. A. (December 1, 1989). "Reaction of trimethylaluminum with carbon monoxide in low-temperature matrixes". American Chemical Society. 111 (25): 9110-9111. Bibcode:1989JAChS.111.9110S. doi:10.1021/ja00207a023. OSTI 6973516.
Tyte, D. C. (1964). "Red (B2Π–A2σ) Band System of Aluminium Monoxide". Nature. 202 (4930): 383. Bibcode:1964Natur.202..383T. doi:10.1038/202383a0. S2CID 4163250.
Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; King, R. Bruce; Schaefer, Iii; Schleyer, Paul v. R.; Robinson, Gregory H. (2008). "Carbene-Stabilized Diphosphorus". Journal of the American Chemical Society. 130 (45): 14970–1. Bibcode:2008JAChS.13014970W. doi:10.1021/ja807828t. PMID 18937460.
Smith, R. E. (1973). "Diatomic Hydride and Deuteride Spectra of the Second Row Transition Metals". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 332 (1588): 113–127. Bibcode:1973RSPSA.332..113S. doi:10.1098/rspa.1973.0015. S2CID 96908213.
McGuire, Joseph C.; Kempter, Charles P. (1960). "Preparation and Properties of Scandium Dihydride". Journal of Chemical Physics. 33 (5): 1584–1585. Bibcode:1960JChPh..33.1584M. doi:10.1063/1.1731452.
Andersson, N.; et al. (2003). "Emission spectra of TiH and TiD near 938 nm". J. Chem. Phys. 118 (8): 10543. Bibcode:2003JChPh.118.3543A. doi:10.1063/1.1539848.
Ram, R. S.; Bernath, P. F. (2003). "Fourier transform emission spectroscopy of the g⁴Δ–a⁴Δ system of FeCl". Journal of Molecular Spectroscopy. 221 (2): 261. Bibcode:2003JMoSp.221..261R. doi:10.1016/S0022-2852(03)00225-X.
Lu, J.; Jian, J.; Huang, W.; Lin, H.; Li, J; Zhou, M. (2016). "Experimental and theoretical identification of the Fe(VII) oxidation state in FeO₄⁻". Physical Chemistry Chemical Physics. 18 (45): 31125–31131. Bibcode:2016PCCP...1831125L. doi:10.1039/C6CP06753K. PMID 27812577.
Cu(−2) have been observed as dimeric anions [Cu₄]^2– in La₂Cu₂In; see Changhoon Lee; Myung-Hwan Whangbo (2008). "Late transition metal anions acting as p-metal elements". Solid State Sciences. 10 (4): 444–449. Bibcode:2008SSSci..10..444K. doi:10.1016/j.solidstatesciences.2007.12.001.
Jackson, Ross A.; Evans, Nicholas J.; Babula, Dawid J.; Horsley Downie, Thomas M.; Charman, Rex S. C.; Neale, Samuel E.; Mahon, Mary F.; Liptrot, David J. (2025-01-28). "Nucleophilicity at copper(-I) in a compound with a Cu–Mg bond". Nature Communications. 16 (1): 1101. Bibcode:2025NatCo..16.1101J. doi:10.1038/s41467-025-56544-z. ISSN 2041-1723. PMC 11775243. PMID 39875432.
Moret, Marc-Etienne; Zhang, Limei; Peters, Jonas C. (2013). "A Polar Copper–Boron One-Electron σ-Bond". J. Am. Chem. Soc. 135 (10): 3792–3795. Bibcode:2013JAChS.135.3792M. doi:10.1021/ja4006578. PMID 23418750.
Zn(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]²⁻, but later shown to be [T–T]⁴⁻ for all these elements) in Ca₅Zn₃ (structure (AE²⁺)₅(T–T)⁴⁻T²⁻⋅4e⁻); see Changhoon Lee; Myung-Hwan Whangbo (2008). "Late transition metal anions acting as p-metal elements". Solid State Sciences. 10 (4): 444–449. Bibcode:2008SSSci..10..444K. doi:10.1016/j.solidstatesciences.2007.12.001. and Changhoon Lee; Myung-Hwan Whangbo; Jürgen Köhler (2010). "Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T–T)^4– and Isolated T^2– Anions in the Polar Intermetallic Cr₅B₃-Type Compounds AE₅T₃ (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)". Zeitschrift für Anorganische und Allgemeine Chemie. 636 (1): 36–40. doi:10.1002/zaac.200900421.
Zn(I) has been reported in decamethyldizincocene; see Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. (2004). "Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond". Science. 305 (5687): 1136–8. Bibcode:2004Sci...305.1136R. doi:10.1126/science.1101356. PMID 15326350. S2CID 38990338.
Colarusso, P.; Guo, B.; Zhang, K.-Q.; Bernath, P. F. (1996). "High-Resolution Infrared Emission Spectrum of Strontium Monofluoride" (PDF). J. Molecular Spectroscopy. 175 (1): 158. Bibcode:1996JMoSp.175..158C. doi:10.1006/jmsp.1996.0019.
Ma, Wen; Herbert, F. William; Senanayake, Sanjaya D.; Yildiz, Bilge (2015-03-09). "Non-equilibrium oxidation states of zirconium during early stages of metal oxidation". Applied Physics Letters. 106 (10). Bibcode:2015ApPhL.106j1603M. doi:10.1063/1.4914180. hdl:1721.1/104888. ISSN 0003-6951.
Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on June 12, 2013.
Palladium(V) has been identified in complexes with organosilicon compounds containing pentacoordinate palladium; see Shimada, Shigeru; Li, Yong-Hua; Choe, Yoong-Kee; Tanaka, Masato; Bao, Ming; Uchimaru, Tadafumi (2007). "Multinuclear palladium compounds containing palladium centers ligated by five silicon atoms". Proceedings of the National Academy of Sciences. 104 (19): 7758–7763. Bibcode:2007PNAS..104.7758S. doi:10.1073/pnas.0700450104. PMC 1876520. PMID 17470819.
Ag(0) has been observed in carbonyl complexes in low-temperature matrices: see McIntosh, D.; Ozin, G. A. (1976). "Synthesis using metal vapors. Silver carbonyls. Matrix infrared, ultraviolet-visible, and electron spin resonance spectra, structures, and bonding of silver tricarbonyl, silver dicarbonyl, silver monocarbonyl, and disilver hexacarbonyl". J. Am. Chem. Soc. 98 (11): 3167–75. Bibcode:1976JAChS..98.3167M. doi:10.1021/ja00427a018.
Te(V) is mentioned by Greenwood and Earnshaw, but they do not give any example of a Te(V) compound. What was long thought to be ditellurium decafluoride (Te₂F₁₀) is actually bis(pentafluorotelluryl) oxide, F₅TeOTeF₅: see Watkins, P. M. (1974). "Ditellurium decafluoride - A Continuing Myth". Journal of Chemical Education. 51 (9): 520–521. Bibcode:1974JChEd..51..520W. doi:10.1021/ed051p520. However, Te(V) has been observed in HTeO⁻, TeO⁻, HTeO−2, and TeO−3; see Kläning, Ulrik K.; Sehested, K. (2001). "Tellurium(V). A Pulse Radiolysis Study". The Journal of Physical Chemistry A. 105 (27): 6637–45. Bibcode:2001JPCA..105.6637K. doi:10.1021/jp010577i.
I(II) is known to exist in monoxide (IO); see Nikitin, I V (31 August 2008). "Halogen monoxides". Russian Chemical Reviews. 77 (8): 739–749. Bibcode:2008RuCRv..77..739N. doi:10.1070/RC2008v077n08ABEH003788. S2CID 250898175.
La(I), Pr(I), Tb(I), Tm(I), and Yb(I) have been observed in MB₈⁻ clusters; see Li, Wan-Lu; Chen, Teng-Teng; Chen, Wei-Jia; Li, Jun; Wang, Lai-Sheng (2021). "Monovalent lanthanide(I) in borozene complexes". Nature Communications. 12 (1): 6467. Bibcode:2021NatCo..12.6467L. doi:10.1038/s41467-021-26785-9. PMC 8578558. PMID 34753931.
SmB₆⁻ cluster anion has been reported and contains Sm in rare oxidation state of +1; see Paul, J. Robinson; Xinxing, Zhang; Tyrel, McQueen; Kit, H. Bowen; Anastassia, N. Alexandrova (2017). "SmB₆^– Cluster Anion: Covalency Involving f Orbitals". J. Phys. Chem. A. 121 (8): 1849–1854. Bibcode:2017JPCA..121.1849R. doi:10.1021/acs.jpca.7b00247. PMID 28182423. S2CID 3723987..
Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Pb(0) carbonyls have been observed in reaction between lead atoms and carbon monoxide; see Ling, Jiang; Qiang, Xu (2005). "Observation of the lead carbonyls Pb_nCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon". The Journal of Chemical Physics. 122 (3): 034505. 122 (3): 34505. Bibcode:2005JChPh.122c4505J. doi:10.1063/1.1834915. ISSN 0021-9606. PMID 15740207. Also, Pb(0) has been observed in [Si^II(Xant)Si^II]PbFe(CO)₄; see Jian Xu; Sudip Pan; Shenglai Yao; Gernot Frenking; Matthias Driess (2022). "The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex ("Plumbylone")". Angewandte Chemie International Edition. 61 (38): e202209442. doi:10.1002/anie.202209442. PMC 9545849. PMID 35848899.{{cite journal}}: CS1 maint: article number as page number (link)
Mosseri, S.; Henglein, A.; Janata, E. (1990). "Trivalent lead as an intermediate in the oxidation of lead(II) and the reduction of lead(IV) species". Journal of Physical Chemistry. 94 (6): 2722–26. Bibcode:1990JPhCh..94.2722M. doi:10.1021/j100369a089.
Pa(II) is known in protactinium monoxide (PaO); see Sellers, Philip A.; Fried, Sherman; Elson, Robert E.; Zachariasen, W. H. (1954). "The Preparation of Some Protactinium Compounds and the Metal". Journal of the American Chemical Society. 76 (23): 5935. Bibcode:1954JAChS..76.5935S. doi:10.1021/ja01652a011.
Preparation of plutonium(VIII) compounds has been claimed, see Zaitsevskii, Andréi; Mosyagin, Nikolai S.; Titov, Anatoly V.; Kiselev, Yuri M. (July 21, 2013). "Relativistic density functional theory modeling of plutonium and americium higher oxide molecules". The Journal of Chemical Physics. 139 (3) 034307. Bibcode:2013JChPh.139c4307Z. doi:10.1063/1.4813284. PMID 23883027. and Kiselev, Yu. M.; Nikonov, M. V.; Dolzhenko, V. D.; Ermilov, A. Yu.; Tananaev, I. G.; Myasoedov, B. F. (January 17, 2014). "On existence and properties of plutonium(VIII) derivatives". Radiochimica Acta. 102 (3): 227–237. doi:10.1515/ract-2014-2146. S2CID 100915090. But their existence has been partially disproven, see Fedosseev, Alexander M.; Bessonov, Alexi A.; Shilov, Vladimir P. (September 5, 2022). "Is octavalent plutonium really formed during oxidation in alkaline aqueous solutions?". Radiochimica Acta. 110 (12): 955–959. doi:10.1515/ract-2022-0056.
Cm(II) has been observed in chloride melts, see Mikheev, Nikolai B.; Auerman, L. N.; Rumer, Igor A.; Kamenskaya, Alla N.; Kazakevich, M. Z. (1992). "The anomalous stabilisation of the oxidation state 2+ of lanthanides and actinides". Russian Chemical Reviews. 61 (10): 990–998. Bibcode:1992RuCRv..61..990M. doi:10.1070/RC1992v061n10ABEH001011. S2CID 250859394.
Domanov, V. P.; Lobanov, Yu. V. (October 2011). "Formation of volatile curium(VI) trioxide CmO₃". Radiochemistry. 53 (5). SP MAIK Nauka/Interperiodica: 453–6. Bibcode:2011Radch..53..453D. doi:10.1134/S1066362211050018. S2CID 98052484.
Sg(0) has been observed in seaborgium hexacarbonyl (Sg(CO)₆); see Even, J.; Yakushev, A.; Dullmann, C. E.; Haba, H.; et al. (2014). "Synthesis and detection of a seaborgium carbonyl complex". Science. 345 (6203): 1491–3. Bibcode:2014Sci...345.1491E. doi:10.1126/science.1255720. PMID 25237098. S2CID 206558746.
Langmuir, Irving (1919). "The arrangement of electrons in atoms and molecules". J. Am. Chem. Soc. 41 (6): 868–934. Bibcode:1919JAChS..41..868L. doi:10.1021/ja02227a002. Archived from the original on 2019-06-21. Retrieved 2019-07-01.
Jensen, W. B. (2007). "the origin of the oxidation-state concept". J. Chem. Educ. 84 (9): 1418–1419. Bibcode:2007JChEd..84.1418J. doi:10.1021/ed084p1418.
Stock, A. (1919). "Einige Nomenklaturfragen der anorganischen Chemie" [Some nomenclature issues of inorganic chemistry]. Angew. Chem. 32 (98): 373–374. Bibcode:1919AngCh..32..373S. doi:10.1002/ange.19190329802. Archived from the original on 2020-08-06. Retrieved 2019-07-01.
Bray, W. C.; Branch, G. E. K. (1913). "Valence and tautomerism". J. Am. Chem. Soc. 35 (10): 1440–1447. Bibcode:1913JAChS..35.1440B. doi:10.1021/ja02199a003. Archived from the original on 2021-02-09. Retrieved 2019-09-16.
Noyes, A. A.; Pitzer, K. S.; Dunn, C. L. (1935). "Argentic salts in acid solution, I. The oxidation and reduction reactions". J. Am. Chem. Soc. 57 (7): 1221–1229. Bibcode:1935JAChS..57.1221N. doi:10.1021/ja01310a018.
Noyes, A. A.; Pitzer, K. S.; Dunn, C. L. (1935). "Argentic salts in acid solution, II. The oxidation state of argentic salts". J. Am. Chem. Soc. 57 (7): 1229–1237. Bibcode:1935JAChS..57.1229N. doi:10.1021/ja01310a019.

chem.harvard.edu

Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on June 12, 2013.

iaea.org (Global: 1,168^th place; English: 1,193^rd place)

inis.iaea.org

Hf(I) has been observed in hafnium monobromide (HfBr), see Marek, G.S.; Troyanov, S.I.; Tsirel'nikov, V.I. (1979). "Кристаллическое строение и термодинамические характеристики монобромидов циркония и гафния / Crystal structure and thermodynamic characteristics of monobromides of zirconium and hafnium". Журнал неорганической химии / Russian Journal of Inorganic Chemistry (in Russian). 24 (4): 890–893.

iupac.org (Global: 538^th place; English: 863^rd place)

goldbook.iupac.org

IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "Oxidation state". doi:10.1351/goldbook.O04365
IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "Oxidation number". doi:10.1351/goldbook.O04363

old.iupac.org

Connelly, N. G.; Damhus, T.; Hartshorn, R. M.; Hutton, A. T. Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005) (PDF). RSC Publishing. Archived (PDF) from the original on 2022-10-09.

libretexts.org (Global: 3,627^th place; English: 2,467^th place)

chem.libretexts.org

"The Two-Electron Bond". Chemistry LibreTexts. June 25, 2016. Archived from the original on February 9, 2021. Retrieved September 1, 2020.

nature.com (Global: 234^th place; English: 397^th place)

Boggiano, Andrew C.; Studvick, Chad M.; Roy Chowdhury, Sabyasachi; Niklas, Julie E.; Tateyama, Haruko; Wu, Hongwei; Leisen, Johannes E.; Kleemiss, Florian; Vlaisavljevich, Bess; Popov, Ivan A.; La Pierre, Henry S. (July 2025). "Praseodymium in the formal +5 oxidation state". Nature Chemistry. 17 (7): 1005–1010. doi:10.1038/s41557-025-01797-w. ISSN 1755-4349.

nevada.edu (Global: low place; English: low place)

radchem.nevada.edu

Th(I) is known in thorium(I) bromide (ThBr); see Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. (2006). "Thorium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 52–160. doi:10.1007/1-4020-3598-5_3. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 2016-03-07.

nih.gov (Global: 4^th place; English: 4^th place)

pubmed.ncbi.nlm.nih.gov

Wang, G.; Zhou, M.; Goettel, G. T.; Schrobilgen, G. J.; Su, J.; Li, J.; Schlöder, T.; Riedel, S. (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Yu, Haoyu S.; Truhlar, Donald G. (2016). "Oxidation State 10 Exists". Angewandte Chemie International Edition. 55 (31): 9004–9006. doi:10.1002/anie.201604670. PMID 27273799.
Karen, Pavel (2015). "Oxidation State, A Long-Standing Issue!". Angewandte Chemie International Edition. 54 (16): 4716–4726. doi:10.1002/anie.201407561. PMC 4506524. PMID 25757151.
Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.
Boronski, Josef T.; Crumpton, Agamemnon E.; Wales, Lewis L.; Aldridge, Simon (2023-06-16). "Diberyllocene, a stable compound of Be(I) with a Be–Be bond". Science. 380 (6650): 1147–1149. Bibcode:2023Sci...380.1147B. doi:10.1126/science.adh4419. ISSN 0036-8075. PMID 37319227. S2CID 259166086.
Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A. (2012). "Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond". Science. 336 (6087): 1420–2. Bibcode:2012Sci...336.1420B. doi:10.1126/science.1221138. PMID 22700924. S2CID 206540959.
Gold heptafluoride, synthesized at low temperature, is calculated to be a complex of molecular fluorine with gold pentafluoride, with F-F bonding in the F₂ evidenced by IR spectroscopy; see Himmel, Daniel; Riedel, Sebastian (2007-05-31). "After 20 Years, Theoretical Evidence That "AuF₇" Is Actually AuF₅·F₂". Inorganic Chemistry. 46 (13): 5338–5342. doi:10.1021/ic700431s. PMID 17511450.
Mg(0) has been synthesized in a compound containing a Na₂Mg₂²⁺ cluster coordinated to a bulky organic ligand; see Rösch, B.; Gentner, T. X.; Eyselein, J.; Langer, J.; Elsen, H.; Li, W.; Harder, S. (2021). "Strongly reducing magnesium(0) complexes". Nature. 592 (7856): 717–721. Bibcode:2021Natur.592..717R. doi:10.1038/s41586-021-03401-w. PMID 33911274. S2CID 233447380
Ram, R. S.; et al. (1998). "Fourier Transform Emission Spectroscopy of the A2D–X2P Transition of SiH and SiD" (PDF). J. Mol. Spectr. 190 (2): 341–352. doi:10.1006/jmsp.1998.7582. PMID 9668026.
Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; King, R. Bruce; Schaefer, Iii; Schleyer, Paul v. R.; Robinson, Gregory H. (2008). "Carbene-Stabilized Diphosphorus". Journal of the American Chemical Society. 130 (45): 14970–1. Bibcode:2008JAChS.13014970W. doi:10.1021/ja807828t. PMID 18937460.
Ellis, Bobby D.; MacDonald, Charles L. B. (2006). "Phosphorus(I) Iodide: A Versatile Metathesis Reagent for the Synthesis of Low Oxidation State Phosphorus Compounds". Inorganic Chemistry. 45 (17): 6864–74. doi:10.1021/ic060186o. PMID 16903744.
Jilek, Robert E.; Tripepi, Giovanna; Urnezius, Eugenijus; Brennessel, William W.; Young, Victor G. Jr.; Ellis, John E. (2007). "Zerovalent titanium–sulfur complexes. Novel dithiocarbamato derivatives of Ti(CO)₆:[Ti(CO)₄(S₂CNR₂)]⁻". Chem. Commun. (25): 2639–2641. doi:10.1039/B700808B. PMID 17579764.
Lu, J.; Jian, J.; Huang, W.; Lin, H.; Li, J; Zhou, M. (2016). "Experimental and theoretical identification of the Fe(VII) oxidation state in FeO₄⁻". Physical Chemistry Chemical Physics. 18 (45): 31125–31131. Bibcode:2016PCCP...1831125L. doi:10.1039/C6CP06753K. PMID 27812577.
Pfirrmann, Stefan; Limberg, Christian; Herwig, Christian; Stößer, Reinhard; Ziemer, Burkhard (2009). "A Dinuclear Nickel(I) Dinitrogen Complex and its Reduction in Single-Electron Steps". Angewandte Chemie International Edition. 48 (18): 3357–61. doi:10.1002/anie.200805862. PMID 19322853.
Carnes, Matthew; Buccella, Daniela; Chen, Judy Y.-C.; Ramirez, Arthur P.; Turro, Nicholas J.; Nuckolls, Colin; Steigerwald, Michael (2009). "A Stable Tetraalkyl Complex of Nickel(IV)". Angewandte Chemie International Edition. 48 (2): 290–4. doi:10.1002/anie.200804435. PMID 19021174.
Jackson, Ross A.; Evans, Nicholas J.; Babula, Dawid J.; Horsley Downie, Thomas M.; Charman, Rex S. C.; Neale, Samuel E.; Mahon, Mary F.; Liptrot, David J. (2025-01-28). "Nucleophilicity at copper(-I) in a compound with a Cu–Mg bond". Nature Communications. 16 (1): 1101. Bibcode:2025NatCo..16.1101J. doi:10.1038/s41467-025-56544-z. ISSN 2041-1723. PMC 11775243. PMID 39875432.
Moret, Marc-Etienne; Zhang, Limei; Peters, Jonas C. (2013). "A Polar Copper–Boron One-Electron σ-Bond". J. Am. Chem. Soc. 135 (10): 3792–3795. Bibcode:2013JAChS.135.3792M. doi:10.1021/ja4006578. PMID 23418750.
Zn(0) has been observed; see Singh, Amit Pratap; Samuel, Prinson P.; Roesky, Herbert W.; Schwarzer, Martin C.; Frenking, Gernot; Sidhu, Navdeep S.; Dittrich, Birger (2013). "A Singlet Biradicaloid Zinc Compound and Its Nonradical Counterpart". J. Am. Chem. Soc. 135 (19): 7324–9. doi:10.1021/ja402351x. PMID 23600486. and Soleilhavoup, Michèle; Bertrand, Guy (2015). "Cyclic (Alkyl)(Amino)Carbenes (CAACs): Stable Carbenes on the Rise". Acc. Chem. Res. 48 (2): 256–266. doi:10.1021/ar5003494. PMID 25515548.
Zn(I) has been reported in decamethyldizincocene; see Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. (2004). "Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond". Science. 305 (5687): 1136–8. Bibcode:2004Sci...305.1136R. doi:10.1126/science.1101356. PMID 15326350. S2CID 38990338.
Abraham, Mariham Y.; Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Shaefer III, Henry F.; Schleyer, P. von R.; Robinson, Gregory H. (2010). "Carbene Stabilization of Diarsenic: From Hypervalency to Allotropy". Chemistry: A European Journal. 16 (2): 432–5. doi:10.1002/chem.200902840. PMID 19937872.
Ellis, Bobby D.; MacDonald, Charles L. B. (2004). "Stabilized Arsenic(I) Iodide: A Ready Source of Arsenic Iodide Fragments and a Useful Reagent for the Generation of Clusters". Inorganic Chemistry. 43 (19): 5981–6. doi:10.1021/ic049281s. PMID 15360247.
Ru(0) is present in the carbonyl-phosphine complex Ru(CO)₂(PPh₃)₃, see Stephane Sentets; Maria del Carmen Rodriguez Martinez; Laure Vendier; Bruno Donnadieu; Vincent Huc; Noël Lugan; Guy Lavigne (2005). "Instant "Base-Promoted" Generation of Roper's-type Ru(0) Complexes Ru(CO)₂(PR₃)₃ from a Simple Carbonylchlororuthenium(II) Precursor". J. Am. Chem. Soc. 127 (42): 14554–14555. doi:10.1021/ja055066e. PMID 16231891.
Rh(VII) is known in the RhO₃⁺ cation, see Da Silva Santos, Mayara; Stüker, Tony; Flach, Max; Ablyasova, Olesya S.; Timm, Martin; von Issendorff, Bernd; Hirsch, Konstantin; Zamudio-Bayer, Vicente; Riedel, Sebastian; Lau, J. Tobias (2022). "The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO3]+". Angew. Chem. Int. Ed. 61 (38) e202207688. doi:10.1002/anie.202207688. PMC 9544489. PMID 35818987.
Pd(I) is known in [Pd₂]²⁺ compounds; see Christoph Fricke; Theresa Sperger; Marvin Mendel; Franziska Schoenebeck (2020). "Catalysis with Palladium(I) Dimers". Angewandte Chemie International Edition. 60 (7): 3355–3366. doi:10.1002/anie.202011825. PMC 7898807. PMID 33058375.
Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on June 12, 2013.
Palladium(V) has been identified in complexes with organosilicon compounds containing pentacoordinate palladium; see Shimada, Shigeru; Li, Yong-Hua; Choe, Yoong-Kee; Tanaka, Masato; Bao, Ming; Uchimaru, Tadafumi (2007). "Multinuclear palladium compounds containing palladium centers ligated by five silicon atoms". Proceedings of the National Academy of Sciences. 104 (19): 7758–7763. Bibcode:2007PNAS..104.7758S. doi:10.1073/pnas.0700450104. PMC 1876520. PMID 17470819.
Guloy, A. M.; Corbett, J. D. (1996). "Synthesis, Structure, and Bonding of Two Lanthanum Indium Germanides with Novel Structures and Properties". Inorganic Chemistry. 35 (9): 2616–22. doi:10.1021/ic951378e. PMID 11666477.
Sn(−3) has been observed in [Sn₂]⁶⁻, e.g. in (Ba₂)⁴⁺(Mg₄)⁸⁺Sn⁴⁻(Sn₂)⁶⁻Sn²⁻ (with square (Sn²⁻)_n sheets), see Papoian, Garegin A.; Hoffmann, Roald (2000). "Hypervalent Bonding in One, Two, and Three Dimensions: Extending the Zintl–Klemm Concept to Nonclassical Electron-Rich Networks". Angew. Chem. Int. Ed. 2000 (39): 2408–2448. doi:10.1002/1521-3773(20000717)39:14<2408::aid-anie2408>3.0.co;2-u. PMID 10941096. Retrieved 2015-02-23.
Sb(I) has been observed in organoantimony compounds; see Šimon, Petr; de Proft, Frank; Jambor, Roman; Růžička, Aleš; Dostál, Libor (2010). "Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures". Angewandte Chemie International Edition. 49 (32): 5468–5471. doi:10.1002/anie.201002209. PMID 20602393.
La(I), Pr(I), Tb(I), Tm(I), and Yb(I) have been observed in MB₈⁻ clusters; see Li, Wan-Lu; Chen, Teng-Teng; Chen, Wei-Jia; Li, Jun; Wang, Lai-Sheng (2021). "Monovalent lanthanide(I) in borozene complexes". Nature Communications. 12 (1): 6467. Bibcode:2021NatCo..12.6467L. doi:10.1038/s41467-021-26785-9. PMC 8578558. PMID 34753931.
Chen, Xin; et al. (2019-12-13). "Lanthanides with Unusually Low Oxidation States in the PrB₃^– and PrB₄^– Boride Clusters". Inorganic Chemistry. 58 (1): 411–418. doi:10.1021/acs.inorgchem.8b02572. PMID 30543295. S2CID 56148031.
All the lanthanides, except Pm, in the +2 oxidation state have been observed in organometallic molecular complexes, see Lanthanides Topple Assumptions and Meyer, G. (2014). "All the Lanthanides Do It and Even Uranium Does Oxidation State +2". Angewandte Chemie International Edition. 53 (14): 3550–51. doi:10.1002/anie.201311325. PMID 24616202.. Additionally, all the lanthanides (La–Lu) form dihydrides (LnH₂), dicarbides (LnC₂), monosulfides (LnS), monoselenides (LnSe), and monotellurides (LnTe), but for most elements these compounds have Ln³⁺ ions with electrons delocalized into conduction bands, e. g. Ln³⁺(H⁻)₂(e⁻).
SmB₆⁻ cluster anion has been reported and contains Sm in rare oxidation state of +1; see Paul, J. Robinson; Xinxing, Zhang; Tyrel, McQueen; Kit, H. Bowen; Anastassia, N. Alexandrova (2017). "SmB₆^– Cluster Anion: Covalency Involving f Orbitals". J. Phys. Chem. A. 121 (8): 1849–1854. Bibcode:2017JPCA..121.1849R. doi:10.1021/acs.jpca.7b00247. PMID 28182423. S2CID 3723987..
Ta(0) is known in Ta(CNDipp)₆; see Khetpakorn Chakarawet; Zachary W. Davis-Gilbert; Stephanie R. Harstad; Victor G. Young Jr.; Jeffrey R. Long; John E. Ellis (2017). "Ta(CNDipp)6: An Isocyanide Analogue of Hexacarbonyltantalum(0)". Angewandte Chemie International Edition. 56 (35): 10577–10581. doi:10.1002/anie.201706323. PMID 28697283. Additionally, Ta(0) has also been previously reported in Ta(bipy)₃, but this has been proven to contain Ta(V).
Ir(VIII) has been observed in iridium tetroxide (IrO₄); see Gong, Yu; Zhou, Mingfei; Kaupp, Martin; Riedel, Sebastian (2009). "Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII". Angewandte Chemie International Edition. 48 (42): 7879–7883. doi:10.1002/anie.200902733. PMID 19593837.
Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Mézaille, Nicolas; Avarvari, Narcis; Maigrot, Nicole; Ricard, Louis; Mathey, François; Le Floch, Pascal; Cataldo, Laurent; Berclaz, Théo; Geoffroy, Michel (1999). "Gold(I) and Gold(0) Complexes of Phosphinine-Based Macrocycles". Angewandte Chemie International Edition. 38 (21): 3194–3197. doi:10.1002/(SICI)1521-3773(19991102)38:21<3194::AID-ANIE3194>3.0.CO;2-O. PMID 10556900.
Dong, Z.-C.; Corbett, J. D. (1996). "Na₂₃K₉Tl_15.3: An Unusual Zintl Compound Containing Apparent Tl₅⁷⁻, Tl₄⁸⁻, Tl₃⁷⁻, and Tl⁵⁻ Anions". Inorganic Chemistry. 35 (11): 3107–12. doi:10.1021/ic960014z. PMID 11666505.
Pb(0) carbonyls have been observed in reaction between lead atoms and carbon monoxide; see Ling, Jiang; Qiang, Xu (2005). "Observation of the lead carbonyls Pb_nCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon". The Journal of Chemical Physics. 122 (3): 034505. 122 (3): 34505. Bibcode:2005JChPh.122c4505J. doi:10.1063/1.1834915. ISSN 0021-9606. PMID 15740207. Also, Pb(0) has been observed in [Si^II(Xant)Si^II]PbFe(CO)₄; see Jian Xu; Sudip Pan; Shenglai Yao; Gernot Frenking; Matthias Driess (2022). "The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex ("Plumbylone")". Angewandte Chemie International Edition. 61 (38): e202209442. doi:10.1002/anie.202209442. PMC 9545849. PMID 35848899.{{cite journal}}: CS1 maint: article number as page number (link)
Siew-Peng Chia; Hong-Wei Xi; Yongxin Li; Kok Hwa Lim; Cheuk-Wai So (2013). "A Base-Stabilized Lead(I) Dimer and an Aromatic Plumbylidenide Anion". Angew. Chem. Int. Ed. 52 (24): 6298–6301. doi:10.1002/anie.201301954. PMID 23629949.
Becker, M.; Förster, C.; Franzen, C.; et al. (2008). "Persistent radicals of trivalent tin and lead". Inorganic Chemistry. 47 (21): 9965–78. doi:10.1021/ic801198p. PMID 18823115.
Bi(I) has been observed in organobismuth compounds; see Šimon, Petr; de Proft, Frank; Jambor, Roman; Růžička, Aleš; Dostál, Libor (2010). "Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures". Angewandte Chemie International Edition. 49 (32): 5468–5471. doi:10.1002/anie.201002209. PMID 20602393.
Th(-I) and U(-I) have been detected in the gas phase as octacarbonyl anions; see Chaoxian, Chi; Sudip, Pan; Jiaye, Jin; Luyan, Meng; Mingbiao, Luo; Lili, Zhao; Mingfei, Zhou; Gernot, Frenking (2019). "Octacarbonyl Ion Complexes of Actinides [An(CO)₈]^+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding". Chemistry (Weinheim an der Bergstrasse, Germany). 25 (50): 11772–11784. 25 (50): 11772–11784. doi:10.1002/chem.201902625. ISSN 0947-6539. PMC 6772027. PMID 31276242.
U(I) has been observed in [U(η⁵-C₅ⁱPr₅)₂]⁻, see Barluzzi, Luciano; Giblin, Sean R.; Mansikkamäki, Akseli; Layfield, Richard A. (2022). "Identification of Oxidation State +1 in a Molecular Uranium Complex". J. Am. Chem. Soc. 144 (40): 18229–18233. doi:10.1021/jacs.2c06519. PMID 36169550. S2CID 252567088. Retrieved 13 July 2023.
U(II) has been observed in [K(2.2.2-Cryptand)][(C₅H₄SiMe₃)₃U], see MacDonald, Matthew R.; Fieser, Megan E.; Bates, Jefferson E.; Ziller, Joseph W.; Furche, Filipp; Evans, William J. (2013). "Identification of the +2 Oxidation State for Uranium in a Crystalline Molecular Complex, [K(2.2.2-Cryptand)][(C₅H₄SiMe₃)₃U]". J. Am. Chem. Soc. 135 (36): 13310–13313. doi:10.1021/ja406791t. PMID 23984753.
Np(II), (III) and (IV) have been observed, see Dutkiewicz, Michał S.; Apostolidis, Christos; Walter, Olaf; Arnold, Polly L (2017). "Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding". Chem. Sci. 8 (4): 2553–2561. doi:10.1039/C7SC00034K. PMC 5431675. PMID 28553487.
Windorff, Cory J.; Chen, Guo P; Cross, Justin N; Evans, William J.; Furche, Filipp; Gaunt, Andrew J.; Janicke, Michael T.; Kozimor, Stosh A.; Scott, Brian L. (2017). "Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of {Pu^II[C₅H₃(SiMe₃)₂]₃}⁻". J. Am. Chem. Soc. 139 (11): 3970–3973. doi:10.1021/jacs.7b00706. PMID 28235179.
Preparation of plutonium(VIII) compounds has been claimed, see Zaitsevskii, Andréi; Mosyagin, Nikolai S.; Titov, Anatoly V.; Kiselev, Yuri M. (July 21, 2013). "Relativistic density functional theory modeling of plutonium and americium higher oxide molecules". The Journal of Chemical Physics. 139 (3) 034307. Bibcode:2013JChPh.139c4307Z. doi:10.1063/1.4813284. PMID 23883027. and Kiselev, Yu. M.; Nikonov, M. V.; Dolzhenko, V. D.; Ermilov, A. Yu.; Tananaev, I. G.; Myasoedov, B. F. (January 17, 2014). "On existence and properties of plutonium(VIII) derivatives". Radiochimica Acta. 102 (3): 227–237. doi:10.1515/ract-2014-2146. S2CID 100915090. But their existence has been partially disproven, see Fedosseev, Alexander M.; Bessonov, Alexi A.; Shilov, Vladimir P. (September 5, 2022). "Is octavalent plutonium really formed during oxidation in alkaline aqueous solutions?". Radiochimica Acta. 110 (12): 955–959. doi:10.1515/ract-2022-0056.
Kovács, Attila; Dau, Phuong D.; Marçalo, Joaquim; Gibson, John K. (2018). "Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States". Inorg. Chem. 57 (15). American Chemical Society: 9453–9467. doi:10.1021/acs.inorgchem.8b01450. OSTI 1631597. PMID 30040397. S2CID 51717837.
Sg(0) has been observed in seaborgium hexacarbonyl (Sg(CO)₆); see Even, J.; Yakushev, A.; Dullmann, C. E.; Haba, H.; et al. (2014). "Synthesis and detection of a seaborgium carbonyl complex". Science. 345 (6203): 1491–3. Bibcode:2014Sci...345.1491E. doi:10.1126/science.1255720. PMID 25237098. S2CID 206558746.
Pauling, L. (1948). "The modern theory of valency". J. Chem. Soc. 1948: 1461–1467. doi:10.1039/JR9480001461. PMID 18893624. Archived from the original on 2021-12-07. Retrieved 2021-11-22.

ncbi.nlm.nih.gov

Karen, Pavel (2015). "Oxidation State, A Long-Standing Issue!". Angewandte Chemie International Edition. 54 (16): 4716–4726. doi:10.1002/anie.201407561. PMC 4506524. PMID 25757151.
Jackson, Ross A.; Evans, Nicholas J.; Babula, Dawid J.; Horsley Downie, Thomas M.; Charman, Rex S. C.; Neale, Samuel E.; Mahon, Mary F.; Liptrot, David J. (2025-01-28). "Nucleophilicity at copper(-I) in a compound with a Cu–Mg bond". Nature Communications. 16 (1): 1101. Bibcode:2025NatCo..16.1101J. doi:10.1038/s41467-025-56544-z. ISSN 2041-1723. PMC 11775243. PMID 39875432.
Rh(VII) is known in the RhO₃⁺ cation, see Da Silva Santos, Mayara; Stüker, Tony; Flach, Max; Ablyasova, Olesya S.; Timm, Martin; von Issendorff, Bernd; Hirsch, Konstantin; Zamudio-Bayer, Vicente; Riedel, Sebastian; Lau, J. Tobias (2022). "The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO3]+". Angew. Chem. Int. Ed. 61 (38) e202207688. doi:10.1002/anie.202207688. PMC 9544489. PMID 35818987.
Pd(I) is known in [Pd₂]²⁺ compounds; see Christoph Fricke; Theresa Sperger; Marvin Mendel; Franziska Schoenebeck (2020). "Catalysis with Palladium(I) Dimers". Angewandte Chemie International Edition. 60 (7): 3355–3366. doi:10.1002/anie.202011825. PMC 7898807. PMID 33058375.
Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on June 12, 2013.
Palladium(V) has been identified in complexes with organosilicon compounds containing pentacoordinate palladium; see Shimada, Shigeru; Li, Yong-Hua; Choe, Yoong-Kee; Tanaka, Masato; Bao, Ming; Uchimaru, Tadafumi (2007). "Multinuclear palladium compounds containing palladium centers ligated by five silicon atoms". Proceedings of the National Academy of Sciences. 104 (19): 7758–7763. Bibcode:2007PNAS..104.7758S. doi:10.1073/pnas.0700450104. PMC 1876520. PMID 17470819.
La(I), Pr(I), Tb(I), Tm(I), and Yb(I) have been observed in MB₈⁻ clusters; see Li, Wan-Lu; Chen, Teng-Teng; Chen, Wei-Jia; Li, Jun; Wang, Lai-Sheng (2021). "Monovalent lanthanide(I) in borozene complexes". Nature Communications. 12 (1): 6467. Bibcode:2021NatCo..12.6467L. doi:10.1038/s41467-021-26785-9. PMC 8578558. PMID 34753931.
Pb(0) carbonyls have been observed in reaction between lead atoms and carbon monoxide; see Ling, Jiang; Qiang, Xu (2005). "Observation of the lead carbonyls Pb_nCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon". The Journal of Chemical Physics. 122 (3): 034505. 122 (3): 34505. Bibcode:2005JChPh.122c4505J. doi:10.1063/1.1834915. ISSN 0021-9606. PMID 15740207. Also, Pb(0) has been observed in [Si^II(Xant)Si^II]PbFe(CO)₄; see Jian Xu; Sudip Pan; Shenglai Yao; Gernot Frenking; Matthias Driess (2022). "The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex ("Plumbylone")". Angewandte Chemie International Edition. 61 (38): e202209442. doi:10.1002/anie.202209442. PMC 9545849. PMID 35848899.{{cite journal}}: CS1 maint: article number as page number (link)
Th(-I) and U(-I) have been detected in the gas phase as octacarbonyl anions; see Chaoxian, Chi; Sudip, Pan; Jiaye, Jin; Luyan, Meng; Mingbiao, Luo; Lili, Zhao; Mingfei, Zhou; Gernot, Frenking (2019). "Octacarbonyl Ion Complexes of Actinides [An(CO)₈]^+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding". Chemistry (Weinheim an der Bergstrasse, Germany). 25 (50): 11772–11784. 25 (50): 11772–11784. doi:10.1002/chem.201902625. ISSN 0947-6539. PMC 6772027. PMID 31276242.
Np(II), (III) and (IV) have been observed, see Dutkiewicz, Michał S.; Apostolidis, Christos; Walter, Olaf; Arnold, Polly L (2017). "Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding". Chem. Sci. 8 (4): 2553–2561. doi:10.1039/C7SC00034K. PMC 5431675. PMID 28553487.

nist.gov (Global: 355^th place; English: 454^th place)

webbook.nist.gov

"HSn". NIST Chemistry WebBook. National Institute of Standards and Technology. Retrieved 23 January 2013.
"SnH3". NIST Chemistry WebBook. National Institure of Standards and Technology. Retrieved 23 January 2013.

osti.gov (Global: 2,036^th place; English: 1,254^th place)

Unstable carbonyl of Al(0) has been detected in reaction of Al₂(CH₃)₆ with carbon monoxide; see Sanchez, Ramiro; Arrington, Caleb; Arrington Jr., C. A. (December 1, 1989). "Reaction of trimethylaluminum with carbon monoxide in low-temperature matrixes". American Chemical Society. 111 (25): 9110-9111. Bibcode:1989JAChS.111.9110S. doi:10.1021/ja00207a023. OSTI 6973516.
Kovács, Attila; Dau, Phuong D.; Marçalo, Joaquim; Gibson, John K. (2018). "Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States". Inorg. Chem. 57 (15). American Chemical Society: 9453–9467. doi:10.1021/acs.inorgchem.8b01450. OSTI 1631597. PMID 30040397. S2CID 51717837.

psi.ch (Global: low place; English: low place)

lch.web.psi.ch

Db(V) has been observed in dubnium pentachloride (DbCl₅); see H. W. Gäggeler (2007). "Gas Phase Chemistry of Superheavy Elements" (PDF). Paul Scherrer Institute. pp. 26–28. Archived from the original (PDF) on 2012-02-20.

psi.ch

Cn(II) has been observed in copernicium selenide (CnSe); see "Annual Report 2015: Laboratory of Radiochemistry and Environmental Chemistry" (PDF). Paul Scherrer Institute. 2015. p. 3.

researchgate.net (Global: 120^th place; English: 125^th place)

Unstable In(0) carbonyls and clusters have been detected, see [2], p. 6.
Sn(−3) has been observed in [Sn₂]⁶⁻, e.g. in (Ba₂)⁴⁺(Mg₄)⁸⁺Sn⁴⁻(Sn₂)⁶⁻Sn²⁻ (with square (Sn²⁻)_n sheets), see Papoian, Garegin A.; Hoffmann, Roald (2000). "Hypervalent Bonding in One, Two, and Three Dimensions: Extending the Zintl–Klemm Concept to Nonclassical Electron-Rich Networks". Angew. Chem. Int. Ed. 2000 (39): 2408–2448. doi:10.1002/1521-3773(20000717)39:14<2408::aid-anie2408>3.0.co;2-u. PMID 10941096. Retrieved 2015-02-23.
Te(III) has been observed in [Te(N(SiMe₃)₂)₂]⁺, see Heinze, Thorsten; Roesky, Herbert W.; Pauer, Frank; Stalke, Dietmar; Sheldrick, George M. (1991). "Synthesis and Structure of the First Tellurium(III) Radical Cation". Angewandte Chemie International Edition. 30 (12): 1678. doi:10.1002/anie.199116771. Retrieved 2015-02-23.

researchwithrutgers.com (Global: low place; English: low place)

Te(−1) has been observed in BaTe₂, see Li, Jing; Guo, Hong You; Mulley, Suzanne; Proserpio, Davide M.; Sironi, Angelo (1994). "Synthesis and crystal structure of a new alkaline-earth metal chalcogenide: Barium ditelluride". Materials Research Bulletin. 29 (10): 1041–1048. doi:10.1016/0025-5408(94)90085-X. Retrieved 2025-11-18.

science.org (Global: 1,160^th place; English: 737^th place)

Boronski, Josef T.; Crumpton, Agamemnon E.; Wales, Lewis L.; Aldridge, Simon (2023-06-16). "Diberyllocene, a stable compound of Be(I) with a Be–Be bond". Science. 380 (6650): 1147–1149. Bibcode:2023Sci...380.1147B. doi:10.1126/science.adh4419. ISSN 0036-8075. PMID 37319227. S2CID 259166086.

sciencedirect.com (Global: 149^th place; English: 178^th place)

Ga(0) is known in gallium monoiodide; see Widdifield, Cory M.; Jurca, Titel; Richeson, Darrin S.; Bryce, David L. (2012-03-16). "Using 69/71Ga solid-state NMR and 127I NQR as probes to elucidate the composition of "GaI"". Polyhedron. 35 (1): 96–100. doi:10.1016/j.poly.2012.01.003. ISSN 0277-5387.

scitation.org (Global: 4,352^nd place; English: 3,229^th place)

aip.scitation.org

Pb(0) carbonyls have been observed in reaction between lead atoms and carbon monoxide; see Ling, Jiang; Qiang, Xu (2005). "Observation of the lead carbonyls Pb_nCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon". The Journal of Chemical Physics. 122 (3): 034505. 122 (3): 34505. Bibcode:2005JChPh.122c4505J. doi:10.1063/1.1834915. ISSN 0021-9606. PMID 15740207. Also, Pb(0) has been observed in [Si^II(Xant)Si^II]PbFe(CO)₄; see Jian Xu; Sudip Pan; Shenglai Yao; Gernot Frenking; Matthias Driess (2022). "The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex ("Plumbylone")". Angewandte Chemie International Edition. 61 (38): e202209442. doi:10.1002/anie.202209442. PMC 9545849. PMID 35848899.{{cite journal}}: CS1 maint: article number as page number (link)

semanticscholar.org (Global: 11^th place; English: 8^th place)

api.semanticscholar.org

Wang, G.; Zhou, M.; Goettel, G. T.; Schrobilgen, G. J.; Su, J.; Li, J.; Schlöder, T.; Riedel, S. (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Karen, P.; McArdle, P.; Takats, J. (2016). "Comprehensive definition of oxidation state (IUPAC Recommendations 2016)". Pure Appl. Chem. 88 (8): 831–839. doi:10.1515/pac-2015-1204. hdl:10852/59520. S2CID 99403810.
Senn, M. S.; Wright, J. P.; Attfield, J. P. (2012). "Charge order and three-site distortions in the Verwey structure of magnetite" (PDF). Nature. 481 (7380): 173–6. Bibcode:2012Natur.481..173S. doi:10.1038/nature10704. hdl:20.500.11820/1b3bb558-52d5-419f-9944-ab917dc95f5e. PMID 22190035. S2CID 4425300. Archived (PDF) from the original on 2022-10-09.
Boronski, Josef T.; Crumpton, Agamemnon E.; Wales, Lewis L.; Aldridge, Simon (2023-06-16). "Diberyllocene, a stable compound of Be(I) with a Be–Be bond". Science. 380 (6650): 1147–1149. Bibcode:2023Sci...380.1147B. doi:10.1126/science.adh4419. ISSN 0036-8075. PMID 37319227. S2CID 259166086.
Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A. (2012). "Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond". Science. 336 (6087): 1420–2. Bibcode:2012Sci...336.1420B. doi:10.1126/science.1221138. PMID 22700924. S2CID 206540959.
Mg(0) has been synthesized in a compound containing a Na₂Mg₂²⁺ cluster coordinated to a bulky organic ligand; see Rösch, B.; Gentner, T. X.; Eyselein, J.; Langer, J.; Elsen, H.; Li, W.; Harder, S. (2021). "Strongly reducing magnesium(0) complexes". Nature. 592 (7856): 717–721. Bibcode:2021Natur.592..717R. doi:10.1038/s41586-021-03401-w. PMID 33911274. S2CID 233447380
Al(−2) has been observed in Sr₁₄[Al₄]₂[Ge]₃, see Wemdorff, Marco; Röhr, Caroline (2007). "Sr₁₄[Al₄]₂[Ge]₃: Eine Zintl-Phase mit isolierten [Ge]^4–- und [Al₄]^8–-Anionen / Sr₁₄[Al₄]₂[Ge]₃: A Zintl Phase with Isolated [Ge]^4–- and [Al₄]^8– Anions". Zeitschrift für Naturforschung B (in German). 62 (10): 1227. doi:10.1515/znb-2007-1001. S2CID 94972243.
Tyte, D. C. (1964). "Red (B2Π–A2σ) Band System of Aluminium Monoxide". Nature. 202 (4930): 383. Bibcode:1964Natur.202..383T. doi:10.1038/202383a0. S2CID 4163250.
Smith, R. E. (1973). "Diatomic Hydride and Deuteride Spectra of the Second Row Transition Metals". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 332 (1588): 113–127. Bibcode:1973RSPSA.332..113S. doi:10.1098/rspa.1973.0015. S2CID 96908213.
Zn(I) has been reported in decamethyldizincocene; see Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. (2004). "Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond". Science. 305 (5687): 1136–8. Bibcode:2004Sci...305.1136R. doi:10.1126/science.1101356. PMID 15326350. S2CID 38990338.
Anastas Sidiropoulos (2019). "Studies of N-heterocyclic Carbene (NHC) Complexes of the Main Group Elements". p. 39. doi:10.4225/03/5B0F4BDF98F60. S2CID 132399530.
I(II) is known to exist in monoxide (IO); see Nikitin, I V (31 August 2008). "Halogen monoxides". Russian Chemical Reviews. 77 (8): 739–749. Bibcode:2008RuCRv..77..739N. doi:10.1070/RC2008v077n08ABEH003788. S2CID 250898175.
Xu, Wei; Lerner, Michael M. (2018). "A New and Facile Route Using Electride Solutions to Intercalate Alkaline Earth Ions into Graphite". Chemistry of Materials. 30 (19): 6930–6935. doi:10.1021/acs.chemmater.8b03421. S2CID 105295721.
Chen, Xin; et al. (2019-12-13). "Lanthanides with Unusually Low Oxidation States in the PrB₃^– and PrB₄^– Boride Clusters". Inorganic Chemistry. 58 (1): 411–418. doi:10.1021/acs.inorgchem.8b02572. PMID 30543295. S2CID 56148031.
SmB₆⁻ cluster anion has been reported and contains Sm in rare oxidation state of +1; see Paul, J. Robinson; Xinxing, Zhang; Tyrel, McQueen; Kit, H. Bowen; Anastassia, N. Alexandrova (2017). "SmB₆^– Cluster Anion: Covalency Involving f Orbitals". J. Phys. Chem. A. 121 (8): 1849–1854. Bibcode:2017JPCA..121.1849R. doi:10.1021/acs.jpca.7b00247. PMID 28182423. S2CID 3723987..
Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
Bi(IV) has been observed; see A. I. Aleksandrov, I. E. Makarov (1987). "Formation of Bi(II) and Bi(IV) in aqueous hydrochloric solutions of Bi(III)". Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science. 36 (2): 217–220. doi:10.1007/BF00959349. S2CID 94865394.
U(I) has been observed in [U(η⁵-C₅ⁱPr₅)₂]⁻, see Barluzzi, Luciano; Giblin, Sean R.; Mansikkamäki, Akseli; Layfield, Richard A. (2022). "Identification of Oxidation State +1 in a Molecular Uranium Complex". J. Am. Chem. Soc. 144 (40): 18229–18233. doi:10.1021/jacs.2c06519. PMID 36169550. S2CID 252567088. Retrieved 13 July 2023.
Preparation of plutonium(VIII) compounds has been claimed, see Zaitsevskii, Andréi; Mosyagin, Nikolai S.; Titov, Anatoly V.; Kiselev, Yuri M. (July 21, 2013). "Relativistic density functional theory modeling of plutonium and americium higher oxide molecules". The Journal of Chemical Physics. 139 (3) 034307. Bibcode:2013JChPh.139c4307Z. doi:10.1063/1.4813284. PMID 23883027. and Kiselev, Yu. M.; Nikonov, M. V.; Dolzhenko, V. D.; Ermilov, A. Yu.; Tananaev, I. G.; Myasoedov, B. F. (January 17, 2014). "On existence and properties of plutonium(VIII) derivatives". Radiochimica Acta. 102 (3): 227–237. doi:10.1515/ract-2014-2146. S2CID 100915090. But their existence has been partially disproven, see Fedosseev, Alexander M.; Bessonov, Alexi A.; Shilov, Vladimir P. (September 5, 2022). "Is octavalent plutonium really formed during oxidation in alkaline aqueous solutions?". Radiochimica Acta. 110 (12): 955–959. doi:10.1515/ract-2022-0056.
Cm(II) has been observed in chloride melts, see Mikheev, Nikolai B.; Auerman, L. N.; Rumer, Igor A.; Kamenskaya, Alla N.; Kazakevich, M. Z. (1992). "The anomalous stabilisation of the oxidation state 2+ of lanthanides and actinides". Russian Chemical Reviews. 61 (10): 990–998. Bibcode:1992RuCRv..61..990M. doi:10.1070/RC1992v061n10ABEH001011. S2CID 250859394.
Kovács, Attila; Dau, Phuong D.; Marçalo, Joaquim; Gibson, John K. (2018). "Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States". Inorg. Chem. 57 (15). American Chemical Society: 9453–9467. doi:10.1021/acs.inorgchem.8b01450. OSTI 1631597. PMID 30040397. S2CID 51717837.
Domanov, V. P.; Lobanov, Yu. V. (October 2011). "Formation of volatile curium(VI) trioxide CmO₃". Radiochemistry. 53 (5). SP MAIK Nauka/Interperiodica: 453–6. Bibcode:2011Radch..53..453D. doi:10.1134/S1066362211050018. S2CID 98052484.
Sg(0) has been observed in seaborgium hexacarbonyl (Sg(CO)₆); see Even, J.; Yakushev, A.; Dullmann, C. E.; Haba, H.; et al. (2014). "Synthesis and detection of a seaborgium carbonyl complex". Science. 345 (6203): 1491–3. Bibcode:2014Sci...345.1491E. doi:10.1126/science.1255720. PMID 25237098. S2CID 206558746.
Sg(VI) has been observed in seaborgium oxide hydroxide (SgO₂(OH)₂); see Huebener, S.; Taut, S.; Vahle, A.; Dressler, R.; et al. (2001). "Physico-chemical characterization of seaborgium as oxide hydroxide" (PDF). Radiochim. Acta. 89 (11–12): 737–741. doi:10.1524/ract.2001.89.11-12.737. S2CID 98583998. Archived from the original (PDF) on 2014-10-25.

springer.com (Global: 274^th place; English: 309^th place)

link.springer.com

Tl(−2) has been observed in Na₂Tl; see Sangster, James (February 2018). "The Systems Li-Tl, Na-Tl and K-Tl". Journal of Phase Equilibria and Diffusion. 39 (1): 74–86. doi:10.1007/s11669-017-0609-9. ISSN 1547-7037.
Tl(−1) has been observed in NaTl; see Sangster, James (February 2018). "The Systems Li-Tl, Na-Tl and K-Tl". Journal of Phase Equilibria and Diffusion. 39 (1): 74–86. doi:10.1007/s11669-017-0609-9. ISSN 1547-7037.

uni-kassel.de (Global: low place; English: low place)

Hofmann, Patrick (1997). Colture. Ein Programm zur interaktiven Visualisierung von Festkörperstrukturen sowie Synthese, Struktur und Eigenschaften von binären und ternären Alkali- und Erdalkalimetallgalliden (PDF) (Thesis) (in German). PhD Thesis, ETH Zurich. p. 72. doi:10.3929/ethz-a-001859893. hdl:20.500.11850/143357. ISBN 978-3-7281-2597-2.

unt.edu (Global: 1,336^th place; English: 769^th place)

digital.library.unt.edu

Pa(II) is known in protactinium monoxide (PaO); see Sellers, Philip A.; Fried, Sherman; Elson, Robert E.; Zachariasen, W. H. (1954). "The Preparation of Some Protactinium Compounds and the Metal". Journal of the American Chemical Society. 76 (23): 5935. Bibcode:1954JAChS..76.5935S. doi:10.1021/ja01652a011.
Es(IV) is known in einsteinium(IV) fluoride (EsF₄); see Kleinschmidt, P. (1994). "Thermochemistry of the actinides". Journal of Alloys and Compounds. 213–214: 169–172. doi:10.1016/0925-8388(94)90898-2.

uwaterloo.ca (Global: 3,153^rd place; English: 2,332^nd place)

bernath.uwaterloo.ca

Zhang, K.Q.; Guo, B.; Braun, V.; Dulick, M.; Bernath, P.F. (1995). "Infrared Emission Spectroscopy of BF and AIF" (PDF). J. Molecular Spectroscopy. 170 (1): 82. Bibcode:1995JMoSp.170...82Z. doi:10.1006/jmsp.1995.1058.
Bernath, P. F.; Black, J. H. & Brault, J. W. (1985). "The spectrum of magnesium hydride" (PDF). Astrophysical Journal. 298: 375. Bibcode:1985ApJ...298..375B. doi:10.1086/163620.. See also Low valent magnesium compounds.
Ram, R. S.; et al. (1998). "Fourier Transform Emission Spectroscopy of the A2D–X2P Transition of SiH and SiD" (PDF). J. Mol. Spectr. 190 (2): 341–352. doi:10.1006/jmsp.1998.7582. PMID 9668026.
Colarusso, P.; Guo, B.; Zhang, K.-Q.; Bernath, P. F. (1996). "High-Resolution Infrared Emission Spectrum of Strontium Monofluoride" (PDF). J. Molecular Spectroscopy. 175 (1): 158. Bibcode:1996JMoSp.175..158C. doi:10.1006/jmsp.1996.0019.

web.archive.org (Global: 1^st place; English: 1^st place)

Schroeder, Melanie, Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden (in German), p. 139, archived from the original on 2020-08-06, retrieved 2020-02-24
"The Two-Electron Bond". Chemistry LibreTexts. June 25, 2016. Archived from the original on February 9, 2021. Retrieved September 1, 2020.
Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on June 12, 2013.
Th(I) is known in thorium(I) bromide (ThBr); see Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. (2006). "Thorium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 52–160. doi:10.1007/1-4020-3598-5_3. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 2016-03-07.
Db(V) has been observed in dubnium pentachloride (DbCl₅); see H. W. Gäggeler (2007). "Gas Phase Chemistry of Superheavy Elements" (PDF). Paul Scherrer Institute. pp. 26–28. Archived from the original (PDF) on 2012-02-20.
Sg(VI) has been observed in seaborgium oxide hydroxide (SgO₂(OH)₂); see Huebener, S.; Taut, S.; Vahle, A.; Dressler, R.; et al. (2001). "Physico-chemical characterization of seaborgium as oxide hydroxide" (PDF). Radiochim. Acta. 89 (11–12): 737–741. doi:10.1524/ract.2001.89.11-12.737. S2CID 98583998. Archived from the original (PDF) on 2014-10-25.
Bh(VII) has been observed in bohrium oxychloride (BhO₃Cl); see Eichler R, Düllmann C, Gäggeler HW, Eichler B, et al. "Gas chemical investigation of bohrium (Bh, element 107)" (PDF). GSI Annual Report 2000. Archived from the original (PDF) on 2008-02-28. Retrieved 2008-02-29.
Langmuir, Irving (1919). "The arrangement of electrons in atoms and molecules". J. Am. Chem. Soc. 41 (6): 868–934. Bibcode:1919JAChS..41..868L. doi:10.1021/ja02227a002. Archived from the original on 2019-06-21. Retrieved 2019-07-01.
"Antoine Laurent Lavoisier The Chemical Revolution – Landmark – American Chemical Society". American Chemical Society. Archived from the original on 5 January 2021. Retrieved 14 July 2018.
"Lavoisier on Elements". Chem125-oyc.webspace.yale.edu. Archived from the original on 13 June 2020. Retrieved 14 July 2018.
Stock, A. (1919). "Einige Nomenklaturfragen der anorganischen Chemie" [Some nomenclature issues of inorganic chemistry]. Angew. Chem. 32 (98): 373–374. Bibcode:1919AngCh..32..373S. doi:10.1002/ange.19190329802. Archived from the original on 2020-08-06. Retrieved 2019-07-01.
Bray, W. C.; Branch, G. E. K. (1913). "Valence and tautomerism". J. Am. Chem. Soc. 35 (10): 1440–1447. Bibcode:1913JAChS..35.1440B. doi:10.1021/ja02199a003. Archived from the original on 2021-02-09. Retrieved 2019-09-16.
Pauling, L. (1948). "The modern theory of valency". J. Chem. Soc. 1948: 1461–1467. doi:10.1039/JR9480001461. PMID 18893624. Archived from the original on 2021-12-07. Retrieved 2021-11-22.

webelements.com (Global: 3,527^th place; English: low place)

Te(I) has been observed in tellurium iodide (TeI), see "Tellurium: tellurium iodide". WebElements.com. Retrieved 2015-02-23.

wiley.com (Global: 222^nd place; English: 297^th place)

onlinelibrary.wiley.com

Be(−2) has been observed in ZrBe₂ and HfBe₂, see Goesten, Maarten G. (2022). "Be–Be π-Bonding and Predicted Superconductivity in MBe2 (M=Zr, Hf)". Angew. Chem. Int. Ed. 61 (4) e202114303. doi:10.1002/anie.202114303.

worldcat.org (Global: 5^th place; English: 5^th place)

search.worldcat.org

Hooydonk, G. Van (1974-05-01). "O n an Ionic Approximation to Chemical Bonding". Zeitschrift für Naturforschung A. 29 (5): 763–767. Bibcode:1974ZNatA..29..763H. doi:10.1515/zna-1974-0517. ISSN 1865-7109.
Boronski, Josef T.; Crumpton, Agamemnon E.; Wales, Lewis L.; Aldridge, Simon (2023-06-16). "Diberyllocene, a stable compound of Be(I) with a Be–Be bond". Science. 380 (6650): 1147–1149. Bibcode:2023Sci...380.1147B. doi:10.1126/science.adh4419. ISSN 0036-8075. PMID 37319227. S2CID 259166086.
Tetrazoles contain a pair of double-bonded nitrogen atoms with oxidation state 0 in the ring. A Synthesis of the parent 1H-tetrazole, CH₂N₄ (two atoms N(0)) is given in Henry, Ronald A.; Finnegan, William G. (1954). "An Improved Procedure for the Deamination of 5-Aminotetrazole". Journal of the American Chemical Society. 76 (1): 290–291. Bibcode:1954JAChS..76..290H. doi:10.1021/ja01630a086. ISSN 0002-7863.
Jackson, Ross A.; Evans, Nicholas J.; Babula, Dawid J.; Horsley Downie, Thomas M.; Charman, Rex S. C.; Neale, Samuel E.; Mahon, Mary F.; Liptrot, David J. (2025-01-28). "Nucleophilicity at copper(-I) in a compound with a Cu–Mg bond". Nature Communications. 16 (1): 1101. Bibcode:2025NatCo..16.1101J. doi:10.1038/s41467-025-56544-z. ISSN 2041-1723. PMC 11775243. PMID 39875432.
Ga(0) is known in gallium monoiodide; see Widdifield, Cory M.; Jurca, Titel; Richeson, Darrin S.; Bryce, David L. (2012-03-16). "Using 69/71Ga solid-state NMR and 127I NQR as probes to elucidate the composition of "GaI"". Polyhedron. 35 (1): 96–100. doi:10.1016/j.poly.2012.01.003. ISSN 0277-5387.
A Se(0) atom has been identified using DFT in [ReOSe(2-pySe)₃]; see Cargnelutti, Roberta; Lang, Ernesto S.; Piquini, Paulo; Abram, Ulrich (2014). "Synthesis and structure of [ReOSe(2-Se-py)3]: A rhenium(V) complex with selenium(0) as a ligand". Inorganic Chemistry Communications. 45: 48–50. doi:10.1016/j.inoche.2014.04.003. ISSN 1387-7003.
Ma, Wen; Herbert, F. William; Senanayake, Sanjaya D.; Yildiz, Bilge (2015-03-09). "Non-equilibrium oxidation states of zirconium during early stages of metal oxidation". Applied Physics Letters. 106 (10). Bibcode:2015ApPhL.106j1603M. doi:10.1063/1.4914180. hdl:1721.1/104888. ISSN 0003-6951.
Boggiano, Andrew C.; Studvick, Chad M.; Roy Chowdhury, Sabyasachi; Niklas, Julie E.; Tateyama, Haruko; Wu, Hongwei; Leisen, Johannes E.; Kleemiss, Florian; Vlaisavljevich, Bess; Popov, Ivan A.; La Pierre, Henry S. (July 2025). "Praseodymium in the formal +5 oxidation state". Nature Chemistry. 17 (7): 1005–1010. doi:10.1038/s41557-025-01797-w. ISSN 1755-4349.
Pt(−2) has been observed in Cs₂Pt, see Karpov, Andrey; Nuss, Jürgen; Wedig, Ulrich; Jansen, Martin (2003-10-13). "Cs2Pt: A Platinide(-II) Exhibiting Complete Charge Separation". Angewandte Chemie International Edition. 42 (39). Wiley: 4818–4821. doi:10.1002/anie.200352314. ISSN 1433-7851..
Brauer, G.; Haucke, W. (1936-06-01). "Kristallstruktur der intermetallischen Phasen MgAu und MgHg". Zeitschrift für Physikalische Chemie. 33B (1): 304–310. doi:10.1515/zpch-1936-3327. ISSN 2196-7156. MgHg then lends itself to an oxidation state of +2 for Mg and -2 for Hg because it consists entirely of these polar bonds with no evidence of electron unpairing. (translated)
Tl(−2) has been observed in Na₂Tl; see Sangster, James (February 2018). "The Systems Li-Tl, Na-Tl and K-Tl". Journal of Phase Equilibria and Diffusion. 39 (1): 74–86. doi:10.1007/s11669-017-0609-9. ISSN 1547-7037.
Tl(−1) has been observed in NaTl; see Sangster, James (February 2018). "The Systems Li-Tl, Na-Tl and K-Tl". Journal of Phase Equilibria and Diffusion. 39 (1): 74–86. doi:10.1007/s11669-017-0609-9. ISSN 1547-7037.
Pb(0) carbonyls have been observed in reaction between lead atoms and carbon monoxide; see Ling, Jiang; Qiang, Xu (2005). "Observation of the lead carbonyls Pb_nCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon". The Journal of Chemical Physics. 122 (3): 034505. 122 (3): 34505. Bibcode:2005JChPh.122c4505J. doi:10.1063/1.1834915. ISSN 0021-9606. PMID 15740207. Also, Pb(0) has been observed in [Si^II(Xant)Si^II]PbFe(CO)₄; see Jian Xu; Sudip Pan; Shenglai Yao; Gernot Frenking; Matthias Driess (2022). "The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex ("Plumbylone")". Angewandte Chemie International Edition. 61 (38): e202209442. doi:10.1002/anie.202209442. PMC 9545849. PMID 35848899.{{cite journal}}: CS1 maint: article number as page number (link)
Pore, Jennifer L.; Gates, Jacklyn M.; Dixon, David A.; Garcia, Fatima H.; Gibson, John K.; Gooding, John A.; McCarthy, Mallory; Orford, Rodney; Shafi, Ziad; Shuh, David K.; Sprouse, Sarah (2025). "Direct identification of Ac and No molecules with an atom-at-a-time technique". Nature. 644. Springer Science and Business Media LLC: 376–380. doi:10.1038/s41586-025-09342-y. ISSN 0028-0836.
Th(-I) and U(-I) have been detected in the gas phase as octacarbonyl anions; see Chaoxian, Chi; Sudip, Pan; Jiaye, Jin; Luyan, Meng; Mingbiao, Luo; Lili, Zhao; Mingfei, Zhou; Gernot, Frenking (2019). "Octacarbonyl Ion Complexes of Actinides [An(CO)₈]^+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding". Chemistry (Weinheim an der Bergstrasse, Germany). 25 (50): 11772–11784. 25 (50): 11772–11784. doi:10.1002/chem.201902625. ISSN 0947-6539. PMC 6772027. PMID 31276242.

yale.edu (Global: 565^th place; English: 460^th place)

chem125-oyc.webspace.yale.edu

"Lavoisier on Elements". Chem125-oyc.webspace.yale.edu. Archived from the original on 13 June 2020. Retrieved 14 July 2018.

zenodo.org (Global: 621^st place; English: 380^th place)

Langmuir, Irving (1919). "The arrangement of electrons in atoms and molecules". J. Am. Chem. Soc. 41 (6): 868–934. Bibcode:1919JAChS..41..868L. doi:10.1021/ja02227a002. Archived from the original on 2019-06-21. Retrieved 2019-07-01.
Stock, A. (1919). "Einige Nomenklaturfragen der anorganischen Chemie" [Some nomenclature issues of inorganic chemistry]. Angew. Chem. 32 (98): 373–374. Bibcode:1919AngCh..32..373S. doi:10.1002/ange.19190329802. Archived from the original on 2020-08-06. Retrieved 2019-07-01.
Bray, W. C.; Branch, G. E. K. (1913). "Valence and tautomerism". J. Am. Chem. Soc. 35 (10): 1440–1447. Bibcode:1913JAChS..35.1440B. doi:10.1021/ja02199a003. Archived from the original on 2021-02-09. Retrieved 2019-09-16.

znaturforsch.com (Global: low place; English: low place)

Ga(−3) has been observed in LaGa, see Dürr, Ines; Bauer, Britta; Röhr, Caroline (2011). "Lanthan-Triel/Tetrel-ide La(Al,Ga)_x(Si,Ge)_1-x. Experimentelle und theoretische Studien zur Stabilität intermetallischer 1:1-Phasen" (PDF). Z. Naturforsch. (in German). 66b: 1107–1121.

Oxidation state (English Wikipedia)

acs.org (Global: 1,248th place; English: 1,104th place)

pubs.acs.org

cen.acs.org

acs.org

aip.org (Global: 2,204th place; English: 1,735th place)

pubs.aip.org

archive.org (Global: 6th place; English: 6th place)

books.google.com (Global: 3rd place; English: 3rd place)

caltech.edu (Global: 887th place; English: 714th place)

authors.library.caltech.edu

cenmag.org (Global: low place; English: low place)

2014.cenmag.org

chemie-master.de (Global: low place; English: low place)

chemistryviews.org (Global: low place; English: low place)

d-nb.info (Global: 511th place; English: 7,028th place)

degruyter.com (Global: 1,425th place; English: 1,138th place)

doi.org (Global: 2nd place; English: 2nd place)

dtu.dk (Global: low place; English: 8,755th place)

orbit.dtu.dk

ed.ac.uk (Global: 1,871st place; English: 1,234th place)

pure.ed.ac.uk

elsevier.com (Global: 610th place; English: 704th place)

linkinghub.elsevier.com

escholarship.org (Global: 1,523rd place; English: 976th place)

ghostarchive.org (Global: 32nd place; English: 21st place)

gsi.de (Global: low place; English: low place)

gsi.de

www-w2k.gsi.de

handle.net (Global: 102nd place; English: 76th place)

hdl.handle.net

harvard.edu (Global: 18th place; English: 17th place)

ui.adsabs.harvard.edu

chem.harvard.edu

iaea.org (Global: 1,168th place; English: 1,193rd place)

inis.iaea.org

iupac.org (Global: 538th place; English: 863rd place)

goldbook.iupac.org

old.iupac.org

libretexts.org (Global: 3,627th place; English: 2,467th place)

chem.libretexts.org

nature.com (Global: 234th place; English: 397th place)

nevada.edu (Global: low place; English: low place)

radchem.nevada.edu

nih.gov (Global: 4th place; English: 4th place)

pubmed.ncbi.nlm.nih.gov

ncbi.nlm.nih.gov

nist.gov (Global: 355th place; English: 454th place)

webbook.nist.gov

osti.gov (Global: 2,036th place; English: 1,254th place)

psi.ch (Global: low place; English: low place)

lch.web.psi.ch

psi.ch

researchgate.net (Global: 120th place; English: 125th place)

researchwithrutgers.com (Global: low place; English: low place)

science.org (Global: 1,160th place; English: 737th place)

sciencedirect.com (Global: 149th place; English: 178th place)

scitation.org (Global: 4,352nd place; English: 3,229th place)

aip.scitation.org

semanticscholar.org (Global: 11th place; English: 8th place)

api.semanticscholar.org

springer.com (Global: 274th place; English: 309th place)

link.springer.com

uni-kassel.de (Global: low place; English: low place)

unt.edu (Global: 1,336th place; English: 769th place)

digital.library.unt.edu

uwaterloo.ca (Global: 3,153rd place; English: 2,332nd place)

bernath.uwaterloo.ca

web.archive.org (Global: 1st place; English: 1st place)

webelements.com (Global: 3,527th place; English: low place)

wiley.com (Global: 222nd place; English: 297th place)

onlinelibrary.wiley.com

worldcat.org (Global: 5th place; English: 5th place)

search.worldcat.org

yale.edu (Global: 565th place; English: 460th place)

chem125-oyc.webspace.yale.edu

zenodo.org (Global: 621st place; English: 380th place)

znaturforsch.com (Global: low place; English: low place)

acs.org (Global: 1,248^th place; English: 1,104^th place)

aip.org (Global: 2,204^th place; English: 1,735^th place)

archive.org (Global: 6^th place; English: 6^th place)

books.google.com (Global: 3^rd place; English: 3^rd place)

caltech.edu (Global: 887^th place; English: 714^th place)

d-nb.info (Global: 511^th place; English: 7,028^th place)

degruyter.com (Global: 1,425^th place; English: 1,138^th place)

doi.org (Global: 2^nd place; English: 2^nd place)

dtu.dk (Global: low place; English: 8,755^th place)

ed.ac.uk (Global: 1,871^st place; English: 1,234^th place)

elsevier.com (Global: 610^th place; English: 704^th place)

escholarship.org (Global: 1,523^rd place; English: 976^th place)

ghostarchive.org (Global: 32^nd place; English: 21^st place)

handle.net (Global: 102^nd place; English: 76^th place)

harvard.edu (Global: 18^th place; English: 17^th place)

iaea.org (Global: 1,168^th place; English: 1,193^rd place)

iupac.org (Global: 538^th place; English: 863^rd place)

libretexts.org (Global: 3,627^th place; English: 2,467^th place)

nature.com (Global: 234^th place; English: 397^th place)

nih.gov (Global: 4^th place; English: 4^th place)

nist.gov (Global: 355^th place; English: 454^th place)

osti.gov (Global: 2,036^th place; English: 1,254^th place)

researchgate.net (Global: 120^th place; English: 125^th place)

science.org (Global: 1,160^th place; English: 737^th place)

sciencedirect.com (Global: 149^th place; English: 178^th place)

scitation.org (Global: 4,352^nd place; English: 3,229^th place)

semanticscholar.org (Global: 11^th place; English: 8^th place)

springer.com (Global: 274^th place; English: 309^th place)

unt.edu (Global: 1,336^th place; English: 769^th place)

uwaterloo.ca (Global: 3,153^rd place; English: 2,332^nd place)

web.archive.org (Global: 1^st place; English: 1^st place)

webelements.com (Global: 3,527^th place; English: low place)

wiley.com (Global: 222^nd place; English: 297^th place)

worldcat.org (Global: 5^th place; English: 5^th place)

yale.edu (Global: 565^th place; English: 460^th place)

zenodo.org (Global: 621^st place; English: 380^th place)