Nonparameterized Molecular Orbital Calculations and Photoelectron Spectroscopy of Open- and Closed-Shell M(IV) M(η⁵-C₅H₅)₂L₂ Complexes

Nonparameterized (Fenske-Hall)-type molecular orbital calculations have been performed on several d⁰, d¹, and d² M(IV) M(η₅-C₅H₅)₂L₂molecules, and the results have been found to be completely compatible with the interpretations obtained from the electron paramagnetic resonance and photoelectron spectral measurements as well as from the crystallographically acquired bond-length and bond-angle data. The MO calculations reveal that the LUMO for the d⁰Ti(IV) complexes and the HOMO for the d¹and nonhydridic d²M(IV) complexes possess analogous orbital characters principally associated with the metal d_z²and d_x²-y²AO's with considerable contributions from the 3p AO's of the sulfur or chlorine L ligands. The relative metal orbital compositions of the HOMO's in the open-shell d¹V(IV) complexes are in remarkable agreement with those obtained from our previously reported dilute single-crystal EPR studies on V(η₅-C₅H₅)S₅and V(η-C₅H₄CH₃)Cl₂. For V(η₅-C₅H₅)S₅the per cent character ratio of 3d_z²/3d_x²-y²= 12.7/1 (EPR) vs. 7.7/1 (MO), while the corresponding ratio of 20.0/1 from the EPR data on V(η-C₅H₄CH₃)Cl₂compares with that of 20.5/1 from the MO computations. Additional information concerning the electronic structure of M(η₅-C₅H₅)₂L₂complexes has been obtained from photoelectron spectroscopy. The PE spectra of M(η⁵-C₅H₅)₂Cl₂and M(η-C₅H₄CH₃)₂Cl₂(where M = Ti, V) are presented and interpreted with the aid of the approximate MO calculations.