Metal–metal interactions in deltahedral dirhoda- and diiridadicarbaboranes

The lowest energy Cp2M2C2Bn−4Hn−2 (M = Rh, Ir; n = 9, 10, and 12) structures are found by density functional theory to be the most spherical deltahedra having the metal atoms at degree 5 vertices and the carbon atoms preferably at degree 4 vertices. Structures with direct surface M–M bonds appear to be energetically more favorable than for the corresponding cobalt derivatives. For the 11-vertex systems Cp2M2C2B7H9 one of the three lowest energy structures is based on the 11-vertex most spherical deltahedron with one of the metal atoms at the unique degree 6 vertex. The 11-vertex polyhedron in one of the other low-energy Cp2M2C2B7H9 structures has a quadrilateral face thereby avoiding the presence of a degree 6 vertex. The Wiberg bond indices (WBIs) for the M–M interactions along deltahedral edges range from 0.36 to 0.40 and can be considered to be formal single bonds. The WBIs for non-adjacent M⋯M interactions are much lower at 0.07–0.12 suggesting weak metal–metal interactions through the center of the deltahedron.