PHOTOELECTRON-SPECTROSCOPY OF F-ELEMENT ORGANOMETALLIC COMPLEXES .12. A COMPARATIVE INVESTIGATION OF THE ELECTRONIC-STRUCTURE OF LANTHANIDE BIS(POLYMETHYLCYCLOPENTADIENYL)HYDROCARBYL COMPLEXES BY RELATIVISTIC AB-INITIO AND DV-X-ALPHA CALCULATIONS AND GAS-PHASE UV PHOTOELECTRON-SPECTROSCOPY

The electronic structure of the bis(polymethylcyclopentadienyl)lanthanide hydrocarbyl complexes Cp'2LnCH(SiMe3)2 and Me2SiCp''2LnCH(SiMe3)2 (Cp' = eta5-(CH3)5C5; Cp'' = eta5-(CH3)4C5; Ln = La, Ce, Nd, Sm, Lu) is investigated by means of relativistic effective core potential ab initio and discrete variational Xalpha calculations and by experimental gas-phase He I/He II photoelectron spectroscopic measurements. The lanthanide-ligand bonding is dominated by interactions involving the metal 5d subshells, while metal 4f orbitals are only marginally involved in the bonding. Good agreement between experimental and calculated ionization energies is found in the case of the lanthanum complex. Metal f-1 ionizations, observed in the He II spectra of the Ln = Ce, Nd, Sm, and Lu complexes, are interpreted on the basis of the ion states generated upon ionization of the corresponding f(n) ground states and are consistent with a gradual energetic stabilization of 4f orbitals across the lanthanide series. Analysis of the photoelectron data indicates pronounced similarity in the lanthanide-ligand bonding on traversing the lanthanide series.