Structure and bonding in a series of neutral and cationic transition metal-benzene eta(6) complexes [M(eta(6)-C6H6)(n+) (M = Ti, V, Cr, Fe, Co, Ni, and Cu). Correlation of charge transfer with the bathochromic shift of the E-1 ring vibration

Geometries and bonding energies have been calculated at the B3LYP/3-21G** a nd B3LYP/DZVP2 levels in a series of [M(eta (6)-C6H6)](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 nu Or near C-6 nu symmetry. Metal-benzene bonding is discu ssed on the basis of MO perturbation schemes. A correlation between the tot al benzene charge and the frequency shift of the El ring vibration (experim entally at 1483 cm(-1) for isolated benzene) is evidenced, allowing interpr etation of experimental data.