Group 9 metallatelluraboranes: Comparison with their sulfur analogues

The lowest energy structures for the Group 9 metallachalcaboranes CpMEBn-2Hn-2 (M = Co, Rh, Ir; E = S, Te) have a central closo MEBn-2 deltahedron consistent with their 2n + 2 skeletal electrons. Stretched edges from the unique degree 6 vertex to a degree 5 vertex are found in the 11-vertex structures. Sulfur prefers energetically degree 4 over degree 5 vertices whereas otherwise analogous structures with tellurium at degree 4 and at degree 5 vertices have similar energies.220