THEORETICAL INVESTIGATION OF THE ELECTRONIC-STRUCTURES OF MIXED-RING SANDWICH MOLECULES [M(ETA(7)-C7H7)(ETA(5)-C5H5)] (M=TI, V, NB OR TA)

Density-functional methods have been used to investigate the valence e lectronic structures of four mixed-ring transition-metal sandwich mole cules, [M(eta(7)-C7H7)(eta(5)-C5H5)] (M = Ti, V, Nb or Ta). Close agre ement with previous experimental data is obtained in all cases for the ionisation energies and localisation properties of the highest occupi ed molecular orbitals. The metal-cyclopentadienyl ring bonding is pred ominantly ionic, while the interaction of the metal with the cyclohept atrienyl ring is found to have a significant covalent component. Analy sis of the composition of the highest occupied molecular orbital corre sponding to the metal-cycloheptatrienyl ring bonding of [Ti(eta(7)-C7H 7)(eta(5)-C5H5)], for which experimental data are not available, sugge sts that it is not appreciably different from that in the Group 5 mole cules.