SPECTROSCOPIC AND MAGNETIC STUDIES OF 3D METALLOCENES

The electronic spectra of the metallocenes, MCp2, and 1, 1'-dimethylmetallocenes, M(MeCp)2, of the first transition series (M=V, Cr, Mn, Fe, Co, Ni) have been measured between 10 and 50 cm-1X103 in isooctane solution. Assignments are proposed for the d-d and charge-transfer transitions observed, these being based in the latter case largely on the band shifts produced by methyl substitution. For the V, Cr, Mn, and Fe compounds the charge-transfer bands appear to correspond only to ligand → metal excitations (e2u→e2g, a1g, e1g) but for the Co compounds (and possibly also for Ni) evidence is also found for metal → ligand (e1g→e2u) transitions. For the V, Cr, Co, and Ni compounds the paramagnetic susceptibilities have been determined in toluene solution by NMR in the temperature range 183-298 K and for the parent compounds also by the Gouy method using solid samples between 83 and 298 K. The V, Cr, and Ni compounds were found to obey the Curie-Weiss law over the ranges studied, but although the V and Ni complexes yielded the spin-only values for the magnetic moment, a substantial orbital contribution was observed for CrCp2 and Cr(MeCp)2. For Co(MeCp)2 the Curie-Weiss law was obeyed over the limited range accessible, although a moment slightly greater than the spin-only value was obtained, and the parent CoCp2 gave a similar moment but deviated markedly from Curie-Weiss behavior. © 1978, American Chemical Society. All rights reserved.