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

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.