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 characterisation of 2MgCl2·4BiCl3·12MeCN as [Mg(MeCN)6]2[Bi4Cl16] and its structural relationships with other complex chlorobismuth(III) anions

Abstract

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, ¹²¹Sb 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 P2₁/a with a= 16.022(11), b= 21.513(22), c= 9.217(10)Å, β= 96.5(1)° 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)Å. 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)Å. 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.