DOI: 10.1039/b924322d

On the electronic structure and stability of icosahedral r-X2Z10H12 and Z12H122- clusters; r = {ortho, meta, para}, X = {C, Si}, Z = {B, Al}

We report on the electronic structure of the 12-vertexicosahedralclustersr-X₂Z₁₀H₁₂and Z₁₂H₁₂^2–, where X = {C,Si} and Z = {B,Al}. The least stablecluster—with the lowest HOMO–LUMO gap (E_g)—corresponds to theortho-X₂Z₁₀H₁₂isomers for all values of X = {C,Si} and Z = {B,Al}. The well-known energetic orderE(para)<E(meta)<E(ortho)forr-carboranes is also valid for all compounds exceptr-C₂Al₁₀H₁₂. Substitution of two atoms ofcarbonorsiliconinto theicosahedralcage B₁₂H₁₂²⁻enhances considerably the stability of the system as analyzed fromE_ggaps, as opposite to Al₁₂H₁₂²⁻, where similar gaps are found upon doublecarbonorsiliconsubstitution regardless of the positions in the cage. In order to highlight similarities and differences in the titleclusters, topological analysis of the electron density was performed, together with analysis of the deviation from polyhedronicosahedralform with (i) volumes, skewness and kurtosis calculations; and (ii) continuous shape measures.