Semiempirical Molecular-Orbital Calculations. IV. Some Metallocenes

Abstract

Charge self-consistent semiempirical calculations including all valence sigma orbitals of the ligands are reported for ferrocene, aminoferrocene, chloroferrocene, and nickelocene. The computations follow the Wolfsberg—Helmholz scheme, and use Slater atomic orbitals which mimic the overlaps, including distance dependence, of the SCF atomic orbitals. An attempt is made to assign electronic excitation energies in a manner consistent with computation and experiment. The only assignment which may be considered reasonably secure is that of the very intense absorption at 51 200 cm−1 which is taken to be the allowed component of the e1g←e1u orbital excitation (fcalc/fobs=0.549/0.691). The ionizing orbital in ferrocene was found to be a1g (−9.78 eV) and in nickelocene was e1g (−6.874 eV). The formal charge on the metal was found to be positive in all cases. A discussion of metal—ligand bonding is included.