Ligand Field Aspects of the Electronic Structure of Molecular Ions of Metal Coordination Compounds

Abstract

The ligand field (l.f.) model describes the electronic structure of the partly filled valence shell of metal coordination compounds by means of three sets of parameters, the ligand field strength parameters, reflecting the perturbation exerted by the ligands upon the metal orbitals, the nephelauxetic ratio which is strictly connected to the covalency of coordination bonds, and the optical electronegativities representing the internal redox properties of metal complexes. The l.f. model has been so far quite successful in describing the structure and properties of chemically stable coordination compounds, and we propose to extend its use to the discussion of some aspects of the electronic structure of molecular ions produced by photoionization, and particularly of the differences from the structure and properties of the parent non-ionized molecules. Four cases will be discussed, as the removal of one electron from the parent molecule can affect (i) inner-core metal orbitals; (ii) inner core ligand orbitals; (iii) metal-centered valence orbitals or (iv) ligand-based valence orbitals.