HALIDE-TRANSFER REACTIONS INVOLVING BISMUTH(III) CHLORIDE - SYNTHESIS AND IDENTIFICATION OF THE TERNARY COMPLEXES BICL3.SBCL5.4MECN, 2MGCL2.4BICL3.12MECN AND 3MGCL2.4BICL3.18MECN - STRUCTURAL CHARACTERIZATION OF 2MGCL2.4BICL3.12MECN AS [MG(MECN)6]2[BI4CL16] AND ITS STRUCTURAL RELATIONSHIPS WITH OTHER COMPLEX CHLOROBISMUTH(III) ANIONS

Reaction (1:1 stoichiometry) of BiCl3 and SbCl5 in acetonitrile provides the ternary complex BiCl3.SbCl5.4MeCN 1 which has been identified (microanalyses, conductivity, IR, Sb-121 NMR and UV-VIS data) as the ionic salt [BiCl2(MeCN)4][SbCl6]. The product 2MgCl2.4BiCl3.12MeCN 2 isolated from the reaction of MgCl2 and BiCl3 (1:2 stoichiometry) in acetonitrile has been characterised by X-ray diffraction studies as the ionic salt [Mg(MeCN)6]2[Bi4Cl16]. Crystals of 2 are monoclinic, space group P2(1)/a with a = 16.022(11), b = 21.513(22), c = 9.217(10) angstrom, beta = 96.5(1)-degrees and Z = 2. Structure refinement gave a final R value of 0.067 for 1635 independent reflections. The six-co-ordinate magnesium atoms of the [Mg(MeCN)6]2+ cations have a distorted octahedral geometry with Mg-N distances in the range 2.20(2)-2.25(3) angstrom. The [Bi4Cl16]4- anions are discrete and centrosymmetric; each tetranuclear Bi(III) unit consists of two pairs of non-equivalent six-co-ordinate bismuth atoms involving terminal Bi-Cl bonds with lengths in the range 2.426(16)-2.552(16), bridging Bi-Cl bonds in the range 2.678(13)-2.976(13) and triply bridging Bi-Cl bonds of 2.930(14) and 3.009(16) angstrom. Each bismuth atom has distorted octahedral geometry. The ternary complex 3MgCl2.4BiCl3.18MeCN 3 isolated from the reaction of MgCl2 and BiCl3 (3:4 stoichiometry) is formulated as the ionic salt [Mg(MeCN)6]3[Bi4Cl18] (by microanalyses, conductivity and IR data). The structure of 2 and possible structures of 3 are discussed within the context of a short review of the structural chemistry of known tetranuclear bismuth(III) chloroanions.