Cotton, F. A..; Lu, J. (1995). «EPR and Crystallographic Studies of Some Reaction Products of VCl4, NbCl4, and TaCl4 with Trialkyl- and Triarylphosphines». Inorg. Chem.34 (10): 2639. doi:10.1021/ic00114a023.
McCarley, Robert E.; Torp, Bruce A. (1963). «The preparation and properties of niobium(IV) compounds. I. Some niobium(IV) halides and their pyridine adducts». Inorg. Chem.2 (3): 540. doi:10.1021/ic50007a029.
Manzer, L.E. (1977). «Preparation of the paramagnetic alkyls bis(cyclopentadienyl)dimethylniobium and bis(methylcyclopentadienyl)dimethyltantalum and some six- and eight-coordinate phosphine derivatives of niobium(IV)». Inorg. Chem.16 (3): 525-528. doi:10.1021/ic50169a004.