A computational study of the lowest singlet and triplet states of neutral and dianionic 1,2-substituted icosahedral and octahedral o-carboranes

This work introduces a calibrated B3LYP/6-31G(d) study on the electronic structure of singlet and triplet neutral species of 1,2-substituted icosahedral 1,2-R-2-1,2-C2B10H10 and octahedral 1,2-R-2-1,2-C2B4H4 molecules with R = {H, OH, SH, NH2, PH2, CH3, SiH3} and their respective dianions formed by proton removal on each R group. A variety of small adiabatic singlet-triplet gaps Delta E-ST are obtained from these systems ranging from 2.93 eV (R = NH2) <= Delta E-ST <= 3.98 eV (R = SiH3) for the icosahedral neutrals and 1.56 eV (R = NH2) <= Delta E-ST <= 4.13 eV (R = SiH3) for the octahedral neutrals, these gaps being globally smaller for the dianionic systems, ranging from 0.94 eV (R- = CH2-) <= Delta E-ST <= 2.01 (R- = e(-)) for the icosahedral dianions 1,2-(R-)(2)-C2B10H10 and 0.91 (R- = CH2-) <= Delta E-ST <= 2.41 (R = SiH2-) for the octahedral dianions 1,2-(R-)(2)-C2B4H4 (R- = e(-), O-, S-, NH-, PH-, CH2-, PH2-). The different gaps lie within or in the neighborhood of the visible region of the electromagetic spectrum. The optimized geometries for the molecular cage remain similar in substituted icosahedral and octahedral singlet states, while a rich variety of different structures can be found for the optimized triplet states. (c) 2006 Wiley Periodicals, Inc.