Ligand-field analysis of transition-metal complexes

Abstract

The aim of this review is to give an account of recent theoretical work (‘Ligand-Field Analysis’) that has both led to clarification of the basic structure of ligand-field theory and has facilitated the acquisition of information about chemical bonding in paramagnetic transition-metal complexes that form insulating crystals. The review begins with a justification in modern terms for the classical crystal-field approach based on a well defined dⁿ-configuration for the metal ion; the central idea is that the ground and low-lying electronic states are based on localized electron wavefunctions because the interelectron repulsion energy is so important in these systems. The ligand-field theory is developed in two stages; first, the group product wavefunction method is used to construct a physically important subspace of many-electron wavefunctions for a transition-metal complex. The full n-electron hamiltonian is then studied in this basis using Lowdin partitioning and the chain formalism of Haydock; a full theoretical characterization of the Ligand-Field hamiltonian, which refers explicitly to only the d-electrons, is given. The paper describes the parametrization of the ligand-field based on the Cellular Ligand Field (CLF) model which explicitly introduces the notion of the chemical functional group to ligand-field theory. The {e ^l _k} -parameters associated with the local interactions of the metal ion and its individual ligands (l) are discussed, and the review includes some general remarks about these quantities for the ligand-fields of some typical transition-metal complexes. A short introduction to the modern electronic structure theory of materials is given as a postlude to the main review.