What determines the solvatochromism of metal-to-ligand charge transfer transitions? A demonstration involving 17 tungsten carbonyl complexes

Abstract

A consistent model which permits rationalization and estimation of the solvatochromic behaviour of coordination compounds with metal-to-ligand charge transfer absorption bands is described. The model shows how the changing relationship between metal-ligand bond polarities in the ground and MLCT excited state determines whether negative, positive, or no solvatochromism results. Data for seventeen mononuclear and binuclear tetra- and pentacarbonyltungsten complexes are analyzed in order to illustrate and substantiate different electronic situations leading to various degrees of solvatochromism. Ligand basicities, calculated Hückel molecular orbital coefficients, ESR coupling constants, and metal fragment oxidation potentials are used to estimate the ability of metal fragments and ligands for charge transfer in the excited state and the resulting solvatochromism of complexes.