The classification and representation of main group element compounds that feature three-center four-electron interactions

Abstract

This article provides a means to classify and represent compounds that feature 3-center 4-electron (3c–4e) interactions in terms of the number of electrons that each atom contributes to the interaction. Specifically, Class I 3c–4e interactions are classified as those in which two atoms provide one electron each and the third atom provides a pair of electrons (i.e. LX₂), while Class II 3c–4e interactions are classified as those in which two atoms each provide a pair of electrons and the third atom contributes none (i.e. L₂Z). These classes can be subcategorized according to the nature of the central atom. Thus, Class I interactions can be categorized according to whether the central atom provides one (i.e. μ–X) or two (i.e. μ–L) electrons, while Class II interactions can be categorized according to whether the central atom provides none (i.e. μ–Z) or two (i.e. μ–L) electrons. The use of appropriate structure-bonding representations for these various interactions provides a means to determine the covalent bond classification of the element of interest.