THE INFLUENCE OF THE CHELATE EFFECT ON SUPRAMOLECULAR STRUCTURE FORMATION - SYNTHESIS AND CRYSTAL-STRUCTURES OF ZINC THIOUREA AND AND THIOSEMICARBAZIDE COMPLEXES WITH TEREPHTHALATE

The lability of the ligand with a potential hydrogen bond donor-hydrog en bond donor arrangement was found to be the predominant factor in de termining the structures of the adducts formed between zinc(II) comple xes of thiourea [tu, NH2C(S)NH2] and thiosemicarbazide [tsc, NH2C(S)NH NH2] and the terephthalate anion [tere, C6H4(CO2-),-1,4]. Reaction of [Zn(tsc)(2)][NO3](2), containing the bidentate thiosemicarbazide ligan d, with sodium terephthalate led to a hydrogen-bonded structure, [Zn(t sc)(2)(OH2)(2)][tere]. 2H(2)O, 1, in which the cations and anions are linked into chains through charge-augmented double hydrogen bonds betw een two NH protons on the tsc ligands and two oxygen lone pairs on the carboxylate. This chain formation is similar to that previously obser ved for related nickel complexes, although there are major differences in the way in which these chains are linked together into sheets. In contrast to the thiosemicarbazide complex, the reaction of [Zn(tu)(4)] [NO3](2), containing unidentate thiourea ligands, with sodium terephth alate led to the formation of a co-ordinatively-bonded polymer, [Zn-2( mu-tu)(tu)(2)(mu-tere)]. 4H(2)O, 2, in which the terephthalate anions have displaced some of the thiourea ligands from each zinc co-ordinati on sphere. The zigzag tapes formed by the terephthalate ligands bridgi ng zinc atoms are linked together into double strands via bridging thi ourea ligands.