Bonding schemes for transition metal clusters

This chapter deals with bonding schemes that treat polyhedral skeleton as a single unit or as an assembly of condensed units. These require a defined number of bonding electrons. It uses the isolobal principle to draw analogies between the transition of metal carbonyl and borane clusters. It also explores the application of the polyhedral skeletal electron pair theory (PSEPT) to metal carbonyl clusters, which provides a rationalization of geometry of the cluster core. The chapter mentions the Wade approach. This determines the number of electrons that a metal-based fragment provides for cluster bonding and rationalizes the structures of transition metal carbonyl clusters that are analogous of boranes and derived anions. It reviews condensed polyhedral structures that are prevalent amongst transition metal carbonyl clusters.