SOLVATOCHROMISM OF DINUCLEAR COMPLEXES - AN ALTERNATIVE EXPLANATION

The very large solvatochromism of the metal to ligand charge-transfer transitions in various, formally nonpolar, ligand-bridged dinuclear metal carbonyl complexes is discussed. The similarity of this behavior to that of related mononuclear species and the good correlations obtained with the “polar” part of McRae's equation are used to demonstrate that dipole-dipole interactions are the main cause of the solvatochromism. This contradicts previous explanations that have attributed the solvatochromism to changes in dispersion forces. It is concluded that, in the simplest approximation, the molecules may be regarded as having polar halves, each of which interacts with the solvent. Detailed interpretation in terms of McRae's equation is not possible without knowing whether the metal to ligand charge-transfer excited state is localized on one metal center or delocalized over both. The data available do not allow us to distinguish between these possibilities. © 1990, American Chemical Society. All rights reserved.