Electronic requirements for macropolyhedral boranes

A retrospective look at the evolution of electron-counting rules is made in pursuit of understanding the nature of bonding in macropolyhedral boranes. The pioneering work of many scientists, especially Lipscomb, Wade, and Mingos, in polyhedral boranes, are considered as bases. Each of these electron-counting rules adopts a particular perspective in its attempt to account for the electronic requirements, its central concern being the recognition that the concerned domain will have a majority of molecules obeying the rules, which will provide the chemist with a handy tool for explorative research. Exceptions do occur to varying degrees. However, if the electron-counting rule is deduced from or substantiated by a mathematical model, it is possible to account for these exceptions. This enhances the understanding of the root motifs and paves the way for further research.