What Electronic Structures and Geometries of Carborane Mono- and ortho-, meta-, and para-Diradicals are Preferred?

Structures, relative stabilities, singlet-triplet gaps, and the ground-state character of mono- and diradicals derived from the three icosahedral carborane cage isomers have been computed by unrestricted broken-symmetry DFT and by CASPT2 methods. Whereas the bond dissociation energies (BDE) leading to the carborane monoradicals are close to the benzene BDE, the most stable carborane radicals are derived from dissociations of hydrogens farthest away from the carbon atoms. All the monomeric carborane diradicals are determined to have singlet ground states. However, the energetic accessibility of triplet states in some of the species offers the potential of building diradical multidimensional carborane network architectures with interesting magnetic properties.