Aplicación de un nuevo método para la determinación teórica de estados de oxidación a partir de cálculos ab initio

Abstract

Since the birth of modern chemistry the concept of oxidation state is widespread in transition metal chemistry and in the study of redox and catalytic reactions. For instance, the geometries and reactivity of transition metal complexes are usually rationalized on the basis of the oxidation state of the metal center. In 2014, a IUPAC’s technical report elaborated by prof. Karen highlighted the need for clarification of this concept. In this paper, several algorithms and rules for the empirical determination of oxidation states are discussed, along with a number of challenging systems. The application of these empirical methods can be tedious for big or complex molecules. Moreover, these algorithms ultimately rely on electronegativity differences between the atoms, and there are several of such scales that can be applied. Thus, there were cases of oxidation state’s assignment carried out by Karen that were ambiguous. On the other hand, Ramos-Cordoba et al have also recently introduced a novel method (effective oxidation states, EOS) to determine theoretically oxidation states from the analysis of the wave function obtained with conventional electronic structure methods. The method can be applied to any system, and for complex molecules requires the definition of fragments/ligands. As a result, the method also provides an index R% to measure to which extent the EOS assignation conforms to the true electron distribution of the molecule. The aim of this work is to apply the EOS method to the same set of challenging systems considered by Karen. We want to see to which extent the empirical and the theoretically derived assignations coincide and whether there is a definite trend in the behavior of the EOS method. The results of the analysis have shown that for most of the studied molecules the EOS method gives the same assignment as the one derived from the empirical rules. Particular exceptions are the molecules with homonuclear bonds without symmetry where the similar atoms makes harder to assign a great electronic distribution to obtain the oxidation state of these atoms