PREPARATION, B-11, C-13 NMR AND VIBRATIONAL-SPECTRA OF THE CLOSO-HEXABORATES [B6H5(CN)]2-AND CIS-[B6H4(CN)2]2-, AND THE CRYSTAL-STRUCTURE OF CS2[B6H5(CN)]

By reaction of Cs2[B6H6] with in situ generated dicyanogen in aqueous alkaline solution the monocyanohydrohexaborate CS2[B6H5(CN)] and the d icyanohydrohexaborate cis-Cs2[B6H4(CN)2] are formed. The compounds hav e been separated by ion exchange chromatography on diethylaminoethyl c ellulose. The crystal structure of Cs2[B6H5(CN)] was determined from s ingle crystal X-ray diffraction analysis; monoclinic, space group P2(1 )/a with a = 9.540(8), b = 9.977(3), c = 10.578(2) angstrom, beta = 10 5.06(2)-degrees. The B-6 octahedron is compressed in the direction of the nearly linear B-CN bond by about 5%, with bond lengths between 1.7 1 and 1.76 angstrom. The B-11 NMR spectra of the two compounds reveal the features of substituted B-6 cages with C4v and C2v point symmetry. In the C-13 NMR spectrum of Cs2[B6H5(CN)] a quartet at -139 ppm with 1J(C,B) 92 Hz is observed. The IR and Raman spectra exhibit very stron g CN stretching bands for Cs2[B6H5(CN)] at 2149, and for cis-CS2[B6H4( CN)2] at 2170 cm-1.