All the lanthanides (La–Lu) in the +2 oxidation state have been observed (except La, Gd, Lu) in dilute, solid solutions of dihalides of these elements in alkaline earth dihalides (see Mall:Holleman&Wiberg) and (except Pm) 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): sid. 3550–51. doi:10.1002/anie.201311325.. 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−).
Am(VII) has been observed in Mall:Chem; see AmericiumArkiverad 9 juni 2019 hämtat från the Wayback Machine., Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010 and Mall:Greenwood&Earnshaw
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Ti(−2), V(−3), Cr(−4), Co(−3), Zr(−2), Nb(−3), Mo(−4), Ru(−2), Rh(−3), Hf(−2), Ta(−3), and W(−4) occur in anionic binary metal carbonyls; see [3], p. 4 (in German); [4], pp. 97–100; [5], p. 239
Al(II) has been observed in aluminium(II) oxide (AlO); see D. C. Tyte (1964). ”Red (B2Π–A2σ) Band System of Aluminium Monoxide”. Nature 202 (4930): sid. 383–384. doi:10.1038/202383a0. Bibcode: 1964Natur.202..383T., and in dialanes (R2Al—AlR2); see Uhl, Werner "Organoelement Compounds Possessing Al—Al, Ga—Ga, In—In, and Tl—Tl Single Bonds" Advances in Organometallic Chemistry Volume 51, 2004, Pages 53–108. doi:10.1016/S0065-3055(03)51002-4
The equilibrium Cl2O6⇌2ClO3 is mentioned by Greenwood and Earnshaw, but it has been refuted, see Lopez, Maria; Juan E. Sicre (1990). ”Physicochemical properties of chlorine oxides. 1. Composition, ultraviolet spectrum, and kinetics of the thermolysis of gaseous dichlorine hexoxide”. J. Phys. Chem. 94 (9): sid. 3860–3863. doi:10.1021/j100372a094., and Cl2O6 is actually chlorine(V,VII) oxide. However, ClO3 has been observed, see Grothe, Hinrich; Willner, Helge (1994). ”Chlorine Trioxide: Spectroscopic Properties, Molecular Structure, and Photochemical Behavior”. Angew. Chem. Int. Ed. 33 (14): sid. 1482–1484. doi:10.1002/anie.199414821.
Ca(I) has been observed; see Krieck, Sven; Görls, Helmar; Westerhausen, Matthias (2010). ”Mechanistic Elucidation of the Formation of the Inverse Ca(I) Sandwich Complex [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] and Stability of Aryl-Substituted Phenylcalcium Complexes”. Journal of the American Chemical Society 132 (35): sid. 12492–501. doi:10.1021/ja105534w. PMID 20718434.
Ti(−1) has been reported in [Ti(bipy)3]−, but was later shown to be Ti(+3); see Bowman, A. C.; England, J.; Sprouls, S.; Weihemüller, T.; Wieghardt, K. (2013). ”Electronic structures of homoleptic [tris(2,2'-bipyridine)M]n complexes of the early transition metals (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta; n = 1+, 0, 1-, 2-, 3-): an experimental and density functional theoretical study.”. Inorganic Chemistry 52 (4): sid. 2242–56. doi:10.1021/ic302799s. PMID 23387926. However, Ti(−1) occurs in [Ti(η-C6H6]− and [Ti(η-C6H5CH3)]−, see Bandy, J. A.; Berry, A.; Green, M. L. H.; Perutz, R. N.; Prout, K.; Verpeautz, J.-N. (1984). ”Synthesis of anionic sandwich compounds: [Ti(η-C6H5R)2]– and the crystal structure of [K(18-crown-6)(µ-H)Mo(η-C5H5)2]”. Inorganic Chemistry 52 (4): sid. 729–731. doi:10.1039/C39840000729.
Fe(VII) and Fe(VIII) have been reported; see Yurii D. Perfiliev; Virender K. Sharma (2008). ”Higher Oxidation States of Iron in Solid State: Synthesis and Their Mössbauer Characterization – Ferrates – ACS Symposium Series (ACS Publications)”. Platinum Metals Review 48 (4): sid. 157–158. doi:10.1595/147106704X10801. However, their existence has been disputed.
Fe(−4), Ru(−4), and Os(−4) have been observed in metal-rich compounds containing octahedral complexes [MIn6−xSnx]; Pt(−3) (as a dimeric anion [Pt–Pt]6−), Cu(−2), Zn(−2), Ag(−2), Cd(−2), Au(−2), and Hg(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]2− for Zn, Cd, Hg, but later shown to be [T–T]4− for all these elements) in La2Pt2In, La2Cu2In, Ca5Au3, Ca5Ag3, Ca5Hg3, Sr5Cd3, Ca5Zn3(structure (AE2+)5(T–T)4−T2−⋅4e−), Yb3Ag2, Ca5Au4, and Ca3Hg2; Au(–3) has been observed in ScAuSn and in other 18-electron half-Heusler compounds. See Changhoon Lee; Myung-Hwan Whangbo (2008). ”Late transition metal anions acting as p-metal elements”. Frontiers in Solid State Chemistry 10 (4): sid. 444–449. doi:10.1016/j.solidstatesciences.2007.12.001. http://www.sciencedirect.com/science/article/pii/S1293255807003883. 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 T2– Anions in the Polar Intermetallic Cr5B3-Type Compounds AE5T3 (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)”. ZAAC 636 (1): sid. 36–40. doi:10.1002/zaac.200900421.
Ni(−2) has been observed in Li2[Ni(1,5-COD)2], see Jonas, Klaus (1975). ”Dilithium-Nickel-Olefin Complexes. Novel Bimetal Complexes Containing a Transition Metal and a Main Group Metal”. Angew. Chem. Int. Ed. 14 (11): sid. 752–753. doi:10.1002/anie.197507521. and Ellis, John E. (2006). ”Adventures with Substances Containing Metals in Negative Oxidation States”. Inorganic Chemistry 45 (8): sid. 3167–86. doi:10.1021/ic052110i.
As(I) has been observed in arsenic(I) iodide (AsI); see 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): sid. 5981–6. doi:10.1021/ic049281s. PMID 15360247.
As(IV) has been observed in arsenic(IV) hydroxide (As(OH)4) and Mall:Chem; see Kläning, Ulrik K.; Bielski, Benon H. J.; Sehested, K. (1989). ”Arsenic(IV). A pulse-radiolysis study”. Inorganic Chemistry 28 (14): sid. 2717–24. doi:10.1021/ic00313a007.
Se(V) has been observed in SeO and HSeO; see Kläning, Ulrik K.; Sehested, K. (1986). ”Selenium(V). A pulse radiolysis study”. Inorganic Chemistry 90 (21): sid. 5460–4. doi:10.1021/j100412a112.
Y(II) has been observed in [(18-crown-6)K][(C5H4SiMe3)3Y]; see MacDonald, M. R.; Ziller, J. W.; Evans, W. J. (2011). ”Synthesis of a Crystalline Molecular Complex of Y2+, [(18-crown-6)K][(C5H4SiMe3)3Y].”. J. Am. Chem. Soc. 133 (40): sid. 15914–17. doi:10.1021/ja207151y.
Zr(−1) has been reported in [Zr(bipy)3]− (see Mall:Greenwood&Earnshaw and Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1995). ”Zirconium” (på german). Lehrbuch der Anorganischen Chemie (101). Walter de Gruyter. Sid. 1413. ISBN 3-11-012641-9.), but was later shown to be Zr(+4); see Bowman, A. C.; England, J.; Sprouls, S.; Weihemüller, T.; Wieghardt, K. (2013). ”Electronic structures of homoleptic [tris(2,2'-bipyridine)M]n complexes of the early transition metals (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta; n = 1+, 0, 1-, 2-, 3-): an experimental and density functional theoretical study.”. Inorganic Chemistry 52 (4): sid. 2242–56. doi:10.1021/ic302799s. PMID 23387926.
Pd(I) has been observed; see Crabtree, R. H. (2002). ”CHEMISTRY: A New Oxidation State for Pd?”. Science 295 (5553): sid. 288–289. doi:10.1126/science.1067921.
Pd(V) has been observed in dioxygenyl hexafluoropalladate; see Falconer, W. E.; Disalvo, F. J.; Edwards, A. J.; Griffiths, J. E.; Sunder, W. E.; Vasile, M. J. (1976). ”Dioxygenyl hexafluoropalladate(V) O2+PdF6−: A quinquevalent compound of palladium”. Journal of Inorganic and Nuclear Chemistry 28, Supplement 1: sid. 59–60. doi:10.1016/0022-1902(76)80595-7.
Pd(VI) complexes have been observed; see Chen, W.; Shimada, Shigeru; Tanaka, Masato (2002). ”Synthesis and Structure of Formally Hexavalent Palladium Complexes”. Science 295 (5553): sid. 308–310. doi:10.1126/science.1067027. Bibcode: 2002Sci...295..308C.
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): sid. 1067–68. doi:10.1021/ic000333x.
In(–5) has been observed in La3InGe, see 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): sid. 2616–22. doi:10.1021/ic951378e.
Sb(IV) has been observed in Mall:Chem, 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): sid. 1599–1604. doi:10.1246/bcsj.73.1599.
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): sid. 520–521. doi:10.1021/ed051p520. However, Te(V) has been observed in Mall:Chem, Mall:Chem, Mall:Chem, and Mall:Chem; see Kläning, Ulrik K.; Sehested, K. (2001). ”Tellurium(V). A Pulse Radiolysis Study”. The Journal of Physical Chemistry A 105 (27): sid. 6637–45. doi:10.1021/jp010577i.
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: sid. 1707–18. doi:10.1039/F19817701707.
All the lanthanides (La–Lu) in the +2 oxidation state have been observed (except La, Gd, Lu) in dilute, solid solutions of dihalides of these elements in alkaline earth dihalides (see Mall:Holleman&Wiberg) and (except Pm) 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): sid. 3550–51. doi:10.1002/anie.201311325.. 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−).
Os(−1) has been observed in Na2[Os4(CO)13] ; see Krause, J.; Siriwardane, Upali; Salupo, Terese A.; Wermer, Joseph R.; Knoeppel, David W.; Shore, Sheldon G. (1993). ”Preparation of [Os3(CO)11]2− and its reactions with Os3(CO)12; structures of [Et4N] [HOs3(CO)11] and H2OsS4(CO)”. Journal of Organometallic Chemistry 454: sid. 263–271. doi:10.1016/0022-328X(93)83250-Y. and Carter, Willie J.; Kelland, John W.; Okrasinski, Stanley J.; Warner, Keith E.; Norton, Jack R. (1982). ”Mononuclear hydrido alkyl carbonyl complexes of osmium and their polynuclear derivatives”. Inorganic Chemistry 21 (11): sid. 3955–3960. doi:10.1021/ic00141a019.
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): sid. 7879–7883. doi:10.1002/anie.200902733.
Ir(IX) has been observed in Mall:Chem; see Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (21 August 2014). ”Identification of an iridium-containing compound with a formal oxidation state of IX”. Nature 514: sid. 475–477. doi:10.1038/nature13795.
Pt(−1) and Pt(−2) have been observed in the barium platinides Ba2Pt and BaPt, respectively: see Karpov, Andrey; Konuma, Mitsuharu; Jansen, Martin (2006). ”An experimental proof for negative oxidation states of platinum: ESCA-measurements on barium platinides”. Chemical Communications (8): sid. 838–840. doi:10.1039/b514631c. PMID 16479284.
Hg(IV) has been observed in mercury(IV) fluoride (HgF4); see Xuefang Wang; Lester Andrews; Sebastian Riedel; Martin Kaupp (2007). ”Mercury Is a Transition Metal: The First Experimental Evidence for HgF4”. Angew. Chem. Int. Ed. 46 (44): sid. 8371–8375. doi:10.1002/anie.200703710. PMID 17899620..
Tl(−5) has been observed in Na23K9Tl15.3, see Dong, Z.-C.; Corbett, J. D. (1996). ”Na23K9Tl15.3: An Unusual Zintl Compound Containing Apparent Tl57-, Tl48−, Tl37−, and Tl5− Anions”. Inorganic Chemistry 35 (11): sid. 3107–12. doi:10.1021/ic960014z.
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): sid. 681–683. doi:10.1002/anie.199406811..
Pb(−2) has been observed in BaPb, see Ferro, Riccardo (2008). Nicholas C. Norman. red. Intermetallic Chemistry. Elsevier. Sid. 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): sid. 6490–94. doi:10.1021/ic000333x.
Pb(+1) and Pb(+3) have been observed in organolead compounds, e.g. hexamethyldiplumbane Pb2(CH3)6; for Pb(I), see 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): sid. 6298–6301. doi:10.1002/anie.201301954..
Bi(+2) has been observed in dibismuthines (R2Bi—BiR2), see Arthur J. Ashe III (1990). ”Thermochromic Distibines and Dibismuthines”. Advances in Organometallic Chemistry 30: sid. 77–97. doi:10.1016/S0065-3055(08)60499-2.
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): sid. 217–220. doi:10.1007/BF00959349.
Ac(II) is known in actinium dihydride (AcH2); see Farr, J; Giorgi, A.L.; Bowman, M.G.; Money, R.K. (1961). ”The crystal structure of actinium metal and actinium hydride”. Journal of Inorganic and Nuclear Chemistry 18: sid. 42–47. doi:10.1016/0022-1902(61)80369-2.
Pa(II) is known in protactinium(II) oxide (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): sid. 5935–5938. doi:10.1021/ja01652a011.
Pu(I) has been observed in plutonium monofluoride (PuF); see Kent, R. A. (1968). ”Mass spectrometric studies of plutonium compounds at high temperatures. II. Enthalpy of sublimation of plutonium(III) fluoride and the dissociation energy of plutonium(I) fluoride”. J. Am. Chem. Soc. 90 (21): sid. 5657–59. doi:10.1021/ja01023a002.
Am(VIII) has been observed; see Nikonov, M. V.; Kiselev, Yu. M.; Myasoedov, B. F. (January 2014). ”Americium volatility from ozonized alkaline solutions”. Radiochemistry 56 (1): sid. 11–18. doi:10.1134/S1066362214010032. Läst 8 mars 2015.
Cm(VI) has been observed in curium trioxide (CmO3) and dioxidocurium(2+) (Mall:Chem); see Domanov, V. P.; Lobanov, Yu. V. (October 2011). ”Formation of volatile curium(VI) trioxide CmO3”. Radiochemistry (SP MAIK Nauka/Interperiodica) 53 (5): sid. 453–6. doi:10.1134/S1066362211050018.
Cm(VIII) has been reported to possibly occur in curium tetroxide (CmO4); see Domanov, V. P. (January 2013). ”Possibility of generation of octavalent curium in the gas phase in the form of volatile tetraoxide CmO4”. Radiochemistry (SP MAIK Nauka/Interperiodica) 55 (1): sid. 46–51. doi:10.1134/S1066362213010098. However, new experiments seem to indicate its nonexistence: Zaitsevskii, Andréi; Schwarz, W H Eugen (April 2014). ”Structures and stability of AnO4 isomers, An = Pu, Am, and Cm: a relativistic density functional study.”. Physical Chemistry Chemical Physics 2014 (16): sid. 8997–9001. doi:10.1039/c4cp00235k. Läst 8 mars 2015.
Negative oxidation states of p-block metals (Al, Ga, In, Sn, Tl, Pb, Bi, Po) and metalloids (Si, Ge, As, Sb, Te, At) may occur in Zintl phases, see: [1], p. 259 and [2] (both in German).
Ti(−2), V(−3), Cr(−4), Co(−3), Zr(−2), Nb(−3), Mo(−4), Ru(−2), Rh(−3), Hf(−2), Ta(−3), and W(−4) occur in anionic binary metal carbonyls; see [3], p. 4 (in German); [4], pp. 97–100; [5], p. 239
In(−2) has been observed in Na2In, see [6], p. 69.
Al(II) has been observed in aluminium(II) oxide (AlO); see D. C. Tyte (1964). ”Red (B2Π–A2σ) Band System of Aluminium Monoxide”. Nature 202 (4930): sid. 383–384. doi:10.1038/202383a0. Bibcode: 1964Natur.202..383T., and in dialanes (R2Al—AlR2); see Uhl, Werner "Organoelement Compounds Possessing Al—Al, Ga—Ga, In—In, and Tl—Tl Single Bonds" Advances in Organometallic Chemistry Volume 51, 2004, Pages 53–108. doi:10.1016/S0065-3055(03)51002-4
Ca(I) has been observed; see Krieck, Sven; Görls, Helmar; Westerhausen, Matthias (2010). ”Mechanistic Elucidation of the Formation of the Inverse Ca(I) Sandwich Complex [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] and Stability of Aryl-Substituted Phenylcalcium Complexes”. Journal of the American Chemical Society 132 (35): sid. 12492–501. doi:10.1021/ja105534w. PMID 20718434.
Ti(−1) has been reported in [Ti(bipy)3]−, but was later shown to be Ti(+3); see Bowman, A. C.; England, J.; Sprouls, S.; Weihemüller, T.; Wieghardt, K. (2013). ”Electronic structures of homoleptic [tris(2,2'-bipyridine)M]n complexes of the early transition metals (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta; n = 1+, 0, 1-, 2-, 3-): an experimental and density functional theoretical study.”. Inorganic Chemistry 52 (4): sid. 2242–56. doi:10.1021/ic302799s. PMID 23387926. However, Ti(−1) occurs in [Ti(η-C6H6]− and [Ti(η-C6H5CH3)]−, see Bandy, J. A.; Berry, A.; Green, M. L. H.; Perutz, R. N.; Prout, K.; Verpeautz, J.-N. (1984). ”Synthesis of anionic sandwich compounds: [Ti(η-C6H5R)2]– and the crystal structure of [K(18-crown-6)(µ-H)Mo(η-C5H5)2]”. Inorganic Chemistry 52 (4): sid. 729–731. doi:10.1039/C39840000729.
As(I) has been observed in arsenic(I) iodide (AsI); see 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): sid. 5981–6. doi:10.1021/ic049281s. PMID 15360247.
Zr(−1) has been reported in [Zr(bipy)3]− (see Mall:Greenwood&Earnshaw and Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1995). ”Zirconium” (på german). Lehrbuch der Anorganischen Chemie (101). Walter de Gruyter. Sid. 1413. ISBN 3-11-012641-9.), but was later shown to be Zr(+4); see Bowman, A. C.; England, J.; Sprouls, S.; Weihemüller, T.; Wieghardt, K. (2013). ”Electronic structures of homoleptic [tris(2,2'-bipyridine)M]n complexes of the early transition metals (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta; n = 1+, 0, 1-, 2-, 3-): an experimental and density functional theoretical study.”. Inorganic Chemistry 52 (4): sid. 2242–56. doi:10.1021/ic302799s. PMID 23387926.
Pt(−1) and Pt(−2) have been observed in the barium platinides Ba2Pt and BaPt, respectively: see Karpov, Andrey; Konuma, Mitsuharu; Jansen, Martin (2006). ”An experimental proof for negative oxidation states of platinum: ESCA-measurements on barium platinides”. Chemical Communications (8): sid. 838–840. doi:10.1039/b514631c. PMID 16479284.
Hg(IV) has been observed in mercury(IV) fluoride (HgF4); see Xuefang Wang; Lester Andrews; Sebastian Riedel; Martin Kaupp (2007). ”Mercury Is a Transition Metal: The First Experimental Evidence for HgF4”. Angew. Chem. Int. Ed. 46 (44): sid. 8371–8375. doi:10.1002/anie.200703710. PMID 17899620..
Fe(−4), Ru(−4), and Os(−4) have been observed in metal-rich compounds containing octahedral complexes [MIn6−xSnx]; Pt(−3) (as a dimeric anion [Pt–Pt]6−), Cu(−2), Zn(−2), Ag(−2), Cd(−2), Au(−2), and Hg(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]2− for Zn, Cd, Hg, but later shown to be [T–T]4− for all these elements) in La2Pt2In, La2Cu2In, Ca5Au3, Ca5Ag3, Ca5Hg3, Sr5Cd3, Ca5Zn3(structure (AE2+)5(T–T)4−T2−⋅4e−), Yb3Ag2, Ca5Au4, and Ca3Hg2; Au(–3) has been observed in ScAuSn and in other 18-electron half-Heusler compounds. See Changhoon Lee; Myung-Hwan Whangbo (2008). ”Late transition metal anions acting as p-metal elements”. Frontiers in Solid State Chemistry 10 (4): sid. 444–449. doi:10.1016/j.solidstatesciences.2007.12.001. http://www.sciencedirect.com/science/article/pii/S1293255807003883. 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 T2– Anions in the Polar Intermetallic Cr5B3-Type Compounds AE5T3 (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)”. ZAAC 636 (1): sid. 36–40. doi:10.1002/zaac.200900421.
Negative oxidation states of p-block metals (Al, Ga, In, Sn, Tl, Pb, Bi, Po) and metalloids (Si, Ge, As, Sb, Te, At) may occur in Zintl phases, see: [1], p. 259 and [2] (both in German).
Am(VII) has been observed in Mall:Chem; see AmericiumArkiverad 9 juni 2019 hämtat från the Wayback Machine., Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010 and Mall:Greenwood&Earnshaw