Macropolyhedral boron-containing cluster chemistry. An X-ray diffraction and nuclear magnetic resonance study of the double cluster 11-vertex: 11-vertex tetracarbaborane C4B18H22

Abstract

The macropolyhedral compound ‘neo’-C₄B₁₈H₂₂ has been examined by single-crystal X-ray diffraction analysis and NMR spectroscopy, and compared with neutral 7,8-C₂B₉H₁₃ and the [7,8-C₂B₉H₁₂]^– anion. Crystal (from hexane–chloroform) were orthorhombic, space group Pbca, with Z= 16, and with a= 23.690(2), b= 21.585(2) and c= 12.3653(8)Å at 150 K. The structure was refined to a wR2 value of 0.1218 using all 4640 unique data. The molecular structure consists of two nido-type {7,8-C₂B₉H₁₁} units symmetrically conjoined at the 9,10 positions such that B(9)–B(9′) is ca. 1.65 Å and B(9)–B(10′) and B(10)–B(9′) are ca. 1.96 Å. Comparison is made with the previously established structure of [nido-7,8-C₂B₉H₁₂]^–. Multiple-element, multiple-resonance, and multidimensional NMR spectroscopy have been used to determine and assign the ¹¹B and ¹H chemical shifts and these are compared with those for neutral nido-7,8,-C₂B₉H₁₃ and for [nido-7,8-C₂B₉H₁₂]^–.