Crystal structures and significance of complexes formed between cadmium bromide and dimethyl sulfoxide

Abstract

Cadmium bromide reacts with dimethyl sulfoxide (dmso) in increasing proportion to produce a series of complexes ranging from a layer-lattice type, through slab and chain structures to ionic derivatives, as shown by X-ray analysis. The layer lattice [{CdBr₂(dmso)}_n] is converted into hydrates [{CdBr₂(dmso)}_n]·nH₂O and [{(CdBr₂)₃(dmso)₂(H₂O)}_n]·nH₂O, both of which have ‘slab’ structures with a CdBr₂ core having the same connectivity as in CdBr₂ itself. Crystalline products [{(CdX₂)₅(dmso)₇}_n], X = Cl or Br, contain two separate chains of compositions (CdX₂)₃(dmso)₄ and (CdX₂)₂(dmso)₃. The former has a condensed chain and the latter a single-chain structure. Single-chain structures are varied, with differing combinations of cadmium centres in six- and five-co-ordination. With potentially cationic and anionic centres, they can be seen as precursors of ionic derivatives [Cd(dmso)₆]²⁺ 2[CdBr₃(dmso)]^–, and [Cd(dmso)₆]²⁺[CdBr₄]^2–. With the ready development of chain structures, Cd differs from Zn (with its strong tetrahedral preference), and also from Hg in showing no tendency towards strong digonal bonding.