Synthesis of the first 11-vertex arachno-dicarbathiaborane anion, [1,6,7-C2SB8H11]−.: Theoretical refinement of its structure

The addition of elemental sulphur to the 10-vertex nido dicarborane [6,9-C2B8H10]2−(2) engenders the new 11-vertex species [1,6,7-C2SB8H11]− (2), which has been structurally characterised using the ab initio/GIAO/NMR method and by deductions made from observations on its reaction chemistry. These combined studies revealed 2 to adopt a structure that is formally derived from the hypothetical parent [closo-B13H13]2− anion by removal of two adjacent six-coordinate and five-coordinate vertices. Since the GIAO calculations of 11B and 13C chemical shifts, employing the RMP2/6-31G* geometry, showed an excellent agreement with the experimental findings, in particular those for <f>δ</f>(11B) and <f>δ</f>(13C) that were computed at the GIAO-RMP2/II<f>′</f> level, the RMP2/6-31G* parameters can be deemed a good representation of the molecular structure of 2 in solution. The other possible structural alternatives of 2 could be ruled out on the basis of geometrical, energetic, and NMR criteria. [Copyright &y& Elsevier]