MACROPOLYHEDRAL BORON-CONTAINING CLUSTER CHEMISTRY - AN X-RAY-DIFFRACTION AND NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE DOUBLE CLUSTER 11-VERTEX 11-VERTEX TETRACARBABORANE C4B18H22/

The macropolyhedral compound 'neo'-C4B18H22 has been examined by singl e-crystal X-ray diffraction analysis and NMR spectroscopy, and compare d with neutral 7,8-C2B9H13 and the [7,8-C2B9H12](-) anion. Crystals (f rom hexane-chloroform) were orthorhombic, space group Pbca, with Z = 1 6, and with a = 23.690(2), b = 21.585(2) and c = 12.3653(8) Angstrom a t 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 t hat B(9)-B(9') is ca. 1.65 Angstrom and 8(9)-B(10') and B(10)-B(9') ar e ca. 1.96 Angstrom. Comparison is made with the previously establishe d structure of [nido-7,8-C2B9H12](-). Multiple-element, multipleresona nce, and multidimensional NMR spectroscopy have been used to determine and assign the B-11 and H-1 chemical shifts and these are compared wi th those for neutral nido-7,8-C2B9H13 and for [nido-7,8-C2B9H12](-).