Electronic structures of two kinds of oligoborane radical anions: Mixed-valence description of a reduced p-phenylenediborane and spin density distributions in distorted octahedral clusters B6Hal6.-, Hal = Cl, Br, I

, und . Main Group Chemistry 5 (4): 267--276 (2006)


D.-functional theory (DFT) calcns. have been carried out for the radical anions 1,4-Mes2B-(C6H4)-BMes2.- (1) (Mes, mesityl), and for B6Cl6.- (2a), B6Br6.- (2b) and B6I6.- (2c). Previous EPR expts. had indicated significant spin delocalization based on 1H, 10B and 11B hyperfine structure 1 and on g factor anisotropy 2a-c. Starting from optimized geometries the calcns. confirmed this notion and yielded quant. information on the spin distribution. While 1 with about 1/3 of spin d. on each of the B atoms and on the org. bridge can be well-formulated as a delocalized (Class III) diboron(III, II) mixed-valent species with a p-phenylene spacer, similarly as the p-phenylenediamine radical cations, the paramagnetic anions 2 are trigonally Jahn-Teller distorted octahedral clusters with variable contributions from the halide substituents to the accommodation of the unpaired electron. While the chloride substituents in 2a participate rather little at the spin distribution, the iodide 2c is calcd. with about equal contributions of 8\% from individual B and I atoms to the singly occupied MO (SOMO). on SciFinder(R)

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