On the Molecular Structure of 7,8-Dicarba-10-thia-nido-undecaborane(10), the First Gaseous 11-Vertex nido Heteroborane Studied by the Combined Electron Diffraction and ab Initio Approach: The NMR Consequence of the Molecular Geometry

Abstract

The molecular structure of 7,8-dicarba-10-thia-nido-undecaborane(10) has been determined by gas-phase electron diffraction and ab initio optimizations at the HF/6-31G* and MP2(fc)/6-31G* levels. IGLO 11B chemical shifts calculations at the DZ level were also carried out. A model based on an icosahedron with one vertex removed and assuming Cs symmetry led to a satisfactory GED fit (R = 0.054). Distortions of the C(7)C(8)B(9)S(10)B(11) pentagonal ring (in relation to the regular pentagon) are more pronounced than those in the opposite hemisphere of the molecule, which consists of a B6 pentagonal pyramid. The plane of the B5 base of this pyramid is almost parallel to that of the C(7)C(8)B(9)B(11) framework, and the sulfur atom lies slightly out of the latter plane. Important structural features include the narrow B(9)S(10)B(11) bond angle [GED: 93.1(6)°; MP2(fc)/6-31G*: 96.6°], the wide C(7)C(8)B(9) angle [GED: 113.8(2)°; MP2(fc)/6-31G*; 114.3°] and large interatomic distances in the B(5)S(10)B(6) triangl...