Ligand effects on the ionization potentials and bond energies of some L1L2Fe2(CO)6 complexes

Abstract

The ionization potentials of the complexes L¹L²Fe₂(CO)₆ where L¹ and L²= SR or PR₂ show dependence on the ionization potential (σ-donor ability) of the ligand. The sulphur ligands are less efficient σ donors than phosphorus and this results in ionization potentials higher by ca. 0·3 eV for corresponding complexes. Complexes with mixed sulphur and phosphorus ligands show intermediate effects.

The average iron–carbon ionic bond dissociation energies [_ionic(Fe–CO)] are largely dependent on the π-acceptor ability of the ligand. Phosphorus ligands, being less efficient π-acceptors than sulphur, cause more electrons to be available for back donation with the antibonding orbitals of CO resulting in a higher _ionic(Fe–CO) of ca. 0·2 eV.