Valence‐Shell Electron‐Pair Repulsion Theory Revisited: An Explanation for Core Polarization

• Published in: Chemistry : a European journal 2019-08, Vol.25 (46), p.10938-10945
• Main Authors: Munárriz, Julen, Calatayud, Mónica, Contreras‐García, Julia
• Format: Article
• Language: English
• Subjects: chemical bonding; Chemical Sciences; Chemistry; Crystallography; Electron distribution; electron localization function; electronic structure; Electrons; Ferricyanide; First principles; Function analysis; Localization; Model testing; or physical chemistry; Organic chemistry; Polarization; Polyhedra; quantum crystallography; Theoretical and; Theory; VSEPR theory
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201902244

Valence‐shell electron‐pair repulsion (VSEPR) theory constitutes one of the pillars of theoretical predictive chemistry. It was proposed even before the advent of the concept of “spin”, and it is still a very useful tool in chemistry. In this article we propose an extension of VSEPR theory to understand the core structure and predict core polarization in the main‐group elements. We show from first principles (Electron Localization Function analysis) how the inner‐ and outer‐core shells are organized. In particular, electrons in these regions are structured following the shape of the dual polyhedron of the valence shell (3rd period) or the equivalent polyhedron (4th and 5th periods). We interpret these results in terms of “hard” and “soft” core character. All the studied systems follow this trend, providing a framework for predicting electron distribution in the core. We also show that lone pairs behave as “standard ligands” in terms of core polarization. The predictive character of the model was tested by proposing the core polarization in different systems not included in the original set (such as XeF4 and [Fe(CN)6]3−) and checking the hypothesis by means of a posteriori calculations. From the experimental point of view, the extension of VSEPR to the core region has consequences for current crystallography research. In particular, it explains the core polarization revealed by high resolution X‐ray experiments. Core values: Here, the extension of valence‐shell electron‐pair repulsion (VSEPR) theory to predict the electron distribution of the core region is explored. The results show that there is an intimate and predictable relationship between the valence and core shells, broadening the scope of VSEPR to the core regions (see figure). In this way, light is shed on the factors governing core polarization, which are important in current crystallography research.