Synthesis, crystal structure, vibrational spectra, and thermal behaviour of [Ph4P](2)[Bi-2(mu-Br)(2)Br-6 (CH3COCH3)(2)]

Abstract

[Ph4P](2)[Bi2Br8(CH3COCH3)(2)] (1) was obtained by the reaction of [Ph4P]Br and BiBr3 in acetone. Single crystals were grown by allowing a layer of n-hexane to diffuse into the acetonic solution of 1. The crystal structure was determined by means of X-ray diffraction. 1 crystallises with monoclinic symmetry in the space group P2(1)/n, No. 14 with the lattice parameters: a = 13.358(2), b = 12.637(2), c = 18.565(3) Angstrom, beta = 102.62(1)degrees, V = 3058.1(8) Angstrom (3) and Z = 4. The structure is characterised by the anion [Bi2Br8(CH3COCH3)(2)](2-) which is embedded in a matrix of [Ph4P](+) cations. The anion can be described as two edge-sharing square pyramids with the apical bromide ions in anti-position. Acetone co-ordinates the bismuth atoms via oxygen atoms and increases the co-ordination number of central bismuth atoms to six which results in the formation of a distorted bi-octahedron. The distortion is due to the difference in terminal and bridging Bi-Br bond lengths. FT-IR and Raman spectroscopic data are presented. In addition, the thermal behaviour of the compound was studied with the aid of TG/DSC coupled with MS revealing that acetone leaves the crystal in two steps. The compound melts at 203 degreesC and transforms into a glass on cooling.