Removal of the transition metal vertex from an "isocloso" metallaborane having 9, 10, or 11 vertices and 2v skeletal electrons leads to a BnHn2- ligand or isoelectronic derivative thereof having one open hexagonal face for hexahapto bonding to the transition metal and 2v - 7 triangular faces. The numbers of available skeletal electrons and orbitals in such isocloso metallaboranes correspond to v 2-electron 3-center bonds in v of the 2v - 4 faces of the original metallaborane deltahedron. This contrasts with the 2-electron v-center core bond and the v surface bonds in the close metal-free BnHn2- and C2Bn-2Hn deltahedra with 2v + 2 skeletal electrons. A diamond-square process removing an M-B edge from an isocloso metallaborane to give an "isonido" metallaborane converts a set of six skeletal orbitals from two 2-electron 3-center bonds into three 2-electron 2-center bonds.