Molecular orbital calculations on transition metal complexes part VII

INDO SCF Molecular Orbital Calculations have been made for manganocene (MnCp₂), its molecular cation (MnCp ₂ ⁺ ) and the ferricenium ion FeCp ₂ ⁺ . The computations yield a high spin ⁶ A _1g (e _2g ² a _1g ¹ e _1g ² ) ground state for MnCp₂, contrary to that which was assumed to interpret the photoelectron spectrum. The lowest energy ionisations from the ⁶ A _1g state have been obtained by differences in total energies of the ion and the neutral molecule. These are in very good agreement with the experimental values. The use of the eigen-values of the neutral molecule to obtain ionisation energies (Koopmans' Theorem) is shown to be inappropriate due to the considerable electronic redistribution which accompanies the formation of the molecular ion from the neutral molecule. The main factor which influences this charge rearrangement is found to be the covalency within the e _1g (d _xz , d _yz ) orbitals.