Molecular structure of gaseous 1,7-dichloro-1,7-dicarba-closo-dodecaborane(12), 1,7-Cl2-1,7-C2B10H10, as studied by electron diffraction and ab lnitio calculations

Abstract

Gas-phase electron diffraction (GED) data for 1,7-dichloro-1,7-dicarba-closo-dodecaborane(12). 1,7-Cl₂-1,7-C₂B₁₀H₁₀, were fitted by a structure possessing overall C_2v, symmetry. Not all of the independent parameters could be refined, and some differences between C–B and B–B bond lengths were fixed at values calculated ab initio.Assumption of local C_5v symmetry for the CB₅ pentagonal pyramids led to the same GED fit (R_G= 0.065) as with a model in which the B₅ rings adjacent to the carbon atoms were not quite regular, as found by ab initio optimisations [HF/6-31G* and MP2(fc)/6-31G*]. Nearest-neighbour C–B and B–B separations do not deviate significantly from normal values, and distortion of the cage from regular icosahedral symmetry is small. The C–Cl bond length, 175.9(9) pm, [MP2/6-31G* 174.9 pm], is shorter than in C(sp³)–Cl systems and longer than in C(sp²)–Cl systems. The geometrical parameters calculated at the MP2(fc)/6-31G* level, as well as ¹¹B NMR chemical shifts, calculated by the individual gauge for localised orbitals method, are in satisfactory agreement with the experimental observations.