Synthesis and Properties of the Octaboron Cluster Series hypercloso‐B₈Cl₈, the Radical Anion hypercloso‐[B₈Cl₈]^.− and the Dianion closo‐[B₈Cl₈]²⁻

Abstract

The synthesis, spectroscopic data, redox properties of B 8 Cl 8 , [B 8 Cl 8 ] *À , and [B 8 Cl 8 ] 2À , and the single-crystal X-ray structure analysis of [Ph 4 P] + 2 [B 8 Cl 8 ] 2À • CH 3 CN are described. Temperaturedependent 11 B NMR measurements and theoretical studies (DFT) concerning the fluxional behavior of [B 8 Cl 8 ] 2À will be discussed. -B 8 Cl 8 reacts with reductants like iodide to the intense purple colored radical anion [B 8 Cl 8 ] *À which is formed as well from B 8 Cl 8 by traces of water. The colorless dianion closo-[B 8 Cl 8 ] 2À is obtained by the reaction of B 8 Cl 8 or [B 8 Cl 8 ] *À with iodide. The single-crystal X-ray structure analysis of [Ph 4 P] + 2 [B 8 Cl 8 ] 2À confirms the dodecahedral D 2d structure of [B 8 Cl 8 ] 2À . The 11 B NMR spectra of [B 8 Cl 8 ] 2À solutions show only one broad signal even at low temperatures due to the fast fluctuation of the [B 8 Cl 8 ] 2À polyhedron. The energy of the C 2v structure isomer of [B 8 Cl 8 ] 2À was calculated by DFT methods to be only 0.6 kcal/ mol higher in energy than the D 2d form, and the activation barrier for the D 2d to C 2v transformation is predicted to be about 0.9 kcal/mol.