4,6-dicarba-8-thia-arachno-nonaborane(10) revisited. Theoretical refinement of its structure

The structure of the nine-vertex arachno-thiadicarbaborane C2SB6H10 has bee n established employing the ab initio/IGLO/NMR method. Theoretical IGLO B-1 1 chemical shifts support C and S atom placements at the 4, 6 and 8 positio ns, respectively, and unambiguously rule out the 4,6,5-C2SB6H10 structural alternative, suggested earlier on the basis of IR and Raman spectroscopy. I mportant structural features of the 4,6,8-C2SB6H10 geometry include a small B(7)-S(8)-B(9) angle (MP2(fc)/6-31G*: 97.9 degrees) and long S-B bonds (MP 2(fc)/6-31G*: 1.905 and 1.924 Angstrom) compared to B-B bonds spanning the 1.71-1.85 Angstrom range.