The results of this have been summarised in a simple but powerful rule, PSEPT, often known as Wade's rules, that can be used to predict the cluster type, closo-, nido-, etc.
They were formulated by Eluvathingal Devassy Jemmis to explain the structures of condensed polyhedral boranes such as B20H16, which are obtained by condensing polyhedral boranes, by sharing a triangular face, an edge, a single vertex or even four vertices.
Three-center two-electron bond, found in electron-deficient compounds such as boranes