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 C2v, 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 C5v symmetry for the CB5 pentagonal pyramids led to the same GED fit (RG= 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.