PREPARATION, B-11 NMR-SPECTRA, VIBRATIONA L-SPECTRA AND NORMAL-COORDINATE ANALYSIS OF TO-BIS-HEXAHYDRO-CLOSO-HEXABORATE,[B6H6-B6H6](2-), AND THE CRYSTAL-STRUCTURE OF [P(C6H5)(4)](2)-CONJUNCTO-[B6H6-B6H6]

By reaction of [B6H6](2-) with dibenzoylperoxide in dichloromethane co njuncto-[B6H6-B6H6](2-) is formed. The product could be separated from excess [B6H6](2-) by ion exchange chromatography on diethylaminoethyl cellulose. The crystal structure of [P(C6H5)(4)](2)-conjuncto-[B6H6-B 6H6] has been determined by single crystal X-ray diffraction analysis; triclinic, space group <P(1)over bar> with a = 10.8315(10), b = 11.24 22(12), c = 20.340(2) Angstrom, alpha = 91.278 degrees (9), beta = 90. 178 degrees (9), gamma = 105.662 degrees(9). The B-11 NMR spectrum rev eals three signals with the intensity ratio 1:1:4, for two equivalent moieties of the conjuncto molecule ion with local C-4v symmetry. The I R and Raman spectra of the deprotonated Cs salts of the B-10, B-11 and their respective D isotopomers of conjuncto-[B6H5-B6H5](4-) exhibit c haracteristic shifts. Using averaged crystallographic data and assumin g idealized D-4h symmetry, normal coordinate analyses have been perfor med based on a modified valence force field. With a set of eleven forc e constants (e.g. f(d)(BB)(conjuncto) = 2.9, f(d)(BB)(cage) = 1.6 mdyn /Angstrom) very good agreement between observed and calculated frequen cies has been achieved. From strong vibrational coupling with the B-6 clusters two vibrations result for the conjuncto B-B bond at 1142/1198 and 292/304cm(-1) for B-11/B-10 species, respectively. They can be as signed as anti-phase and in-phase motions of the conjuncto B atoms rel ated to the equatorial B-4 planes.