Is It Possible To Determine Oxidation States for Atoms in Molecules Using Density-Based Quantities? An Information-Theoretic Approach and Conceptual Density Functional Theory Study

The oxidation state, also called oxidation number, of atoms in molecules is a fundamental chemical concept. It is defined as the charge of an atom in a molecule after the ionic approximation of its heteronuclear bonds is applied. Even though for simple molecules the assignment of oxidation states is straightforward, redundancy and ambiguity do exist for others. In this work, we present a density-based framework to determine the oxidation state using the quantities from the information-theoretic approach. As a proof of concept, we examined six elements for a total of 49 molecules. Strong linear correlations were obtained with Shannon entropy, Ghosh-Berkowitz-Parr entropy, information gain, relative Renyi entropy of orders 2 and 3, and Hirshfeld charge. We also discovered that the crystal radius of elements plays the key role in rationalizing the system dependent nature of these strong linear correlations. The validity and effectiveness of our results were demonstrated by the examples of molecules containing elements with two or more oxidation states. Our results should be applicable to more complicated systems in assigning different oxidation states.