Let's Not Forget About Electronic Correlation

Abstract It has been known for over 30 years that electronic correlation has a profound effect on the ground and excited state energies of classical coordination complexes containing more than one unpaired electron. Subdisciplines of inorganic chemistry such as organometallic chemistry and the chemistry of multiply bonded metal clusters have not been too concerned about these effects, since molecules belonging to those classes are typically diamagnetic or, less frequently, paramagnetic for only one unpaired electron. As a result, the description of these systems is often based on the use of more or less quantitative “monoelectronic” arguments, i.e., on the application of valence bond or molecular orbital considerations. This Comment will discuss the limitations of this approach and illustrate the importance of electronic correlation effects (a) in the reaction mechanism of organometallic reactions where the metal has an intermediate formal oxidation state, and (b) in the understanding of ground state properties of certain dinuclear clusters that “fail” to exhibit a high order metal-metal interaction.