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(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 discussed on the basis of MO perturbation schemes. A correlation between the total benzene charge and the frequency shift of the El ring vibration (experimentally at 1483 cm(-1) for isolated benzene) is evidenced, allowing interpretation of experimental data.