Darstellung, ¹¹B-NMR-Spektren, Schwingungsspektren und Normalkoordinatenanalyse von conjuncto-Bis-hexahydro-closo-hexaborat, [B₆H₆-B₆H₆]^2-, sowie Kristallstruktur von [P(C₆H₅)₄]₂-conjuncto-[B₆H₆-B₆H₆] / Preparation, ¹¹B NMR Spectra, Vibrational Spectra and Normal Coordinate Analysis of conjuncto-Bis-hexahydro-closo-hexaborate, [B₆H₆-B₆H₆]^2-, and the Crystal Structure of [ P(C₆H₅)₄]₂-conjuncto-[B₆H₆-B₆H₆]

Abstract

By reaction of [B 6 H 6 ] 2- with dibenzoylperoxide in dichloromethane conjuncto-[B 6 H 6 - B 6 H 6 ] 2- is formed. The product could be separated from excess [B 6 H 6 ] 2- by ion exchange chromatography on diethylaminoethyl cellulose. The crystal structure of [P(C 6 H 5 ) 4 ] 2 -conjuncto- [B 6 H 6 -B 6 H 6 ] has been determined by single crystal X-ray diffraction analysis; triclinic, space group P1̄ with a = 10.8315(10), b = 11,2422( 12), c = 20.340(2) Å, α = 91.278° (9), β = 90.178° (9), γ = 105.662°(9). The 11 B NMR spectrum reveals three signals with the intensity ratio 1:1:4, for two equivalent moieties of the conjuncto molecule ion with local C 4v symmetry. The IR and Raman spectra of the deprotonated Cs salts of the 10 B, 11 B and their respective D isotopomers of conjuncto-[B 6 H 5 -B 6 H 5 ] 4- exhibit characteristic shifts. Using averaged crystallographic data and assuming idealized D 4h symmetry, normal coordinate analyses have been performed based on a modified valence force field. With a set of eleven force constants (e.g. f d (BB) conjuncto = 2.9, f d (BB) cage = 1.6 mdyn/Å) very good agreement between observed and calculated frequencies 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 11 B/ 10 B species, respectively. They can be assigned as anti-phase and in-phase motions of the conjuncto B atoms related to the equatorial B 4 planes.