Structure and Bonding in a Series of Neutral and Cationic Transition Metal−Benzene η6 Complexes [M(η6-C6H6)]n+ (M = Ti, V, Cr, Fe, Co, Ni, and Cu). Correlation of Charge Transfer with the Bathochromic Shift of the E1 Ring Vibration

Geometries and bonding energies have been calculated at the B3LYP/3-21G** and B3LYP/DZVP2 levels in a series of [M(η 6 -C 6 H 6 )] n + complexes where M = Ti, Cr, Co ( n = 0), V ( n = 3), Fe ( n = 0, 2), Ni ( n = 0, 2, 4), and Cu ( n = 1) with C 6 v or near C 6 v symmetry. Metal−benzene bonding is discussed on the basis of MO perturbation schemes. A correlation between the total benzene charge and the frequency shift of the E 1 ring vibration (experimentally at 1483 cm -1 for isolated benzene) is evidenced, allowing interpretation of experimental data.