Interpretation of formal oxidation number in transition metal complex by quantum chemical calculation

Abstract

A formal oxidation number in a transition metal complex is an important factor for estimating geometric structures, understanding the reactivity of homogeneous catalysts, elucidating the redox properties, and so on. On the other hand, a charge obtained by a quantum chemical calculation is often used to analyze an electronic state of a transition metal. However, the charge, which contains various effects, sometimes shows a different behavior from the formal oxidation number. In this study, we propose a scheme to interpret the formal oxidation number based on quantum chemical calculations. The scheme gives the same results of the formal oxidation number as the IUPAC’s definition. Furthermore, the charge is divided into three contributions: formal oxidation number, bonding, and remaining contributions. Each contribution is expected to be used for reactivity analysis and as new descriptors for machine learning in chemistry.