Delineating the principles controlling polymer formation and topology in zinc(II)- and cadmium(II)-dithiophosphate adducts of diimine-type ligands

The crystal structure determination of polymeric [Cd(S2P(OCy)2)2(3-NC5H4C(H)NNC(H)C5H4N-3)·(CHCl3)2]∞, where Cy is cyclohexyl and the bridging ligand is 3-pyridinealdazine, shows that the cadmium atom exists within a trans-N2S4 donor set and that the resultant polymer topology is of a step-ladder. It is argued that this is the expected structure for the compound as it concurs with the structure of the related iso-propyl derivative. Indeed, in most cases polymer topology in related cadmium dithiophosphate systems is controlled by the nature of the bridging diimine-type ligand. By contrast, in the analogous zinc dithiophosphate adducts, controlling polymer topology is possible by systematically varying the steric profile of the dithiophosphate-bound R groups, a phenomenon ascribed to the fact that in the zinc system, the zinc–ligand distances being shorter, bring all the components of the structure in close proximity and thereby exacerbates steric effects. An overview of our accomplishments in this area ‘crystal engineering of coordination polymers’ is presented herein.