Modification of the Coordination Behaviour of 4,6-Dimethylpyrimidine-2-thiol with Divalent Cadmium at pH 5.5: A Supramolecular Assembly Generated by Axially Directed Zigzag Weaving of Tripolar Zwitterionic Motifs Through Alternate Pairs of Charge-Assisted C(sp(2))-H center dot center dot center dot Cl and N(sp(2))-H center dot center dot center dot Cl Interactions in Solid State

At pH 5.5, coordination between Cd2+ and 4,6-dimethylpyrimidine-2-thiol was studied using CdCl2 and Cd(NO3)(2). For both of these, the same complex, bis-4,6-dimethylpyrimidinium-2-thiolato cadmium (II) chloride was invariably formed. It crystallized from water in the space group P2(1)/c, Z = 4 (a = 12.955(2) , b = 8.429(1) , c = 15.727(2) , beta = 97.19(0)A degrees), displaying a distorted tetrahedral molecular geometry characterized by a [CdCl2S2](2(-)) chromophore. The negative charge on the coordination zone is intramolecularly compensated by protonation of one azomethine N in each of the two thiolpyrimidine ligands, resulting in a tripolar zwitterion; its aqueous solution is consequently acidic and highly conducting. The crystal structure is mainly characterized by two kinds of charge-driven H-bonding interactions generated in pairs by the inversion symmetry of the space group and translation symmetry of its periodic lattice. This ultimately results in extensive intermolecular interactions, forming left handed zigzag H-bond networks and a consequent supramolecular growth along b. Spectroscopic studies agree well with the proposed molecular structure. The aqueous solubility of the complex and a high 50% lethal dose (mice) of its ligand seem to indicate development of the pyrimidinethiol moiety into a prospective antidote to Cd2+ toxicity.