Clusters with interstitial atoms from the p-block: How do Wade's rules handle them?

Abstract

This article considers the application of Wade's rules of cluster electron counting to low oxidation state transition metal clusters containing interstitial atoms from the p-block. The discussion focuses on the classification of clusters using Wade's rules, and on their successes and failures which can be rationalized in terms of the relationship of a particular metal cluster to a deltahedral [B_nH_n]²⁻ anionic prototype cluster. The need to extend the electron counting schemes to the Polyhedral Skeletal Electron Pair Theory (PSEPT) is seen when we consider frameworks such as the trigonal prism which is considered as a 3-connected polyhedron rather than as a hypho-cluster. A square- antiprism M_X-skeleton is ambiguous: such clusters may or may not obey Wade's rules. The application of Wade's rules to condensed polyhedra and the limitations of the rules in this case are considered. Finally, we discuss examples of gold clusters containing interstitial atoms from the p-block and illustrate that the bonding in and the shapes of these clusters are not satisfactorily rationalized by either the Wade or PSEPT approach.

This article is dedicated to Ken Wade whose thought-provoking undergraduate lectures provided inspiration at a time when Wade's rules were breaking new ground.