A Unified Approach to Electron Counting in Main-Group Clusters

Abstract

A unified approach to electron counting in main-group cluster chemistry is presented, wherein the different classes, electron-rich, electron-precise, and electron-deficient, are viewed simply as different regions of a continuum defined by two variables, vertex count and valence electron count. The diverse structural chemistry of all main-group clusters can then be reconciled by recognizing that, within the confines of a fixed vertex count, each reduction of two in the total electron count must be associated with a distortion that destabilizes a single molecular orbital. This simple tenet affords a consistent framework for correlating structure with electron count across the entire spectrum of clusters, including the recently discovered hypoelectronic class. The different ways in which structure responds to changes in electron count within the different domains emerges as a logical consequence of the nature (bonding or nonbonding) of the particular orbital that is destabilized.