Isocloso versus closo deltahedra in slightly hypoelectronic supraicosahedral 14-vertex dimetallaboranes with 28 skeletal electrons: relationship to icosahedral dimetallaboranes

Structures of the slightly hypoelectronic 14-vertex species Cp2M2B12H12 (M = Rh, Ir) and Cp2M′2C2B10H12 (M′ = Ru, Os) with 28 Wadean skeletal electrons, including the experimentally known Cp*2Ru2C2B10H12, have been optimized by density functional theory. All low-energy such structures have the metal atoms located at degree 6 vertices. The lowest energy structures have central M2B12 and M′2C2B10 deltahedra with three degree 6 vertices, one degree 4 vertex, ten degree 5 vertices, and the metal atoms located at non-adjacent non-antipodal degree 6 vertices similar to meta isomers of icosahedral dimetallaboranes. Slightly higher energy structures are based on the same central deltahedron but with the metal atoms located at adjacent degree 6 vertices similar to ortho isomers of dimetallaboranes. Isomeric structures with central M2B12 and M′2C2B10 central closo deltahedra, namely bicapped hexagonal antiprisms with the metal atoms in antipodal positions at the two degree 6 vertices similar to the para isomers of icosahedral dimetallaboranes, also lie at low energies.