Bonding studies of transition metal complexes : I. He(I) photoelectron spectra of d0 silylmethyl and neopentyl derivatives of group iv a metals

Abstract

The He(I) photoelectron spectra of the compounds MR 4 and M′R′ 4 (M = Ti, Zr, or Hf; M′ = M, Ge, or Sn; R = Me 3CCH 2; R′ = Me 3SiCH 2) have been measured. From these and published data the spectra have been assigned in terms of a localised bond model assuming a tetrahedral MC 4 framework. The highest occupied molecular orbital (MO) lies in the range 8 – 9 eV and is assigned to σ(M—C) or σ(M′—C). For isoleptic transition metal alkyls, the highest MO is very insensitive to the nature of the central metal, while for corresponding Group IVB complexes the expected decrease in first ionisation potential (IP) due to progressive decrease in electronegativity with atomic number is observed. Small inductive effects of the ligands account for the different IP's of silylmethyl compounds compared with neopentyl derivatives. Observed stability trends are not related to ground state electronic effects. Broadening is observed for the first band in the zirconium and hafnium neopentyls and this is ascribed to a distortion of the MC 4 framework to D 2 d .