Backbone flexibility and counterion effects on the structure and thermal properties of Di(thiourea)zinc dicarboxylate coordination polymers

The reaction between [Zn(tu)(4)]Cl-2 and the appropriate sodium dicarboxylate has been shown to give the coordination polymers [Zn(tu)(2)(mu-succinate)](n), (7), [Zn(tu)(2)(mu-itaconate)](n) (8), [Zn(tu)(2)(mu-ethylmalonate)](n) (9), [Zn(tu)(2)(mu-1,3-phenylene-diacetate)], (10) and {[Zn(tu)(2)(mu-mesaconate)].2H(2)O}(n) (11), all of which have been crystallographically characterised. The crystal structures of 7-9 demonstrate that these compounds form helical structures in which the dicarboxylates adopt conformations with the relative positions of the carboxylate groups similar to those in constrained anions such as phthalate. The role of the chloride counterion in the starting material has been explored by investigating the reactions of [Zn(tu)(4)](NO3)(2) with a range of dicarboxylates. Although in the majority of cases the counterion was shown to have no effect, in the case of fumarate, a hydrated coordination polymer {[Zn(tu)(2)(mu-fumarate)].2H(2)O}(n) (12) was observed in addition to the anhydrous product [Zn(tu)(2)(mu-fumarate)](n) (1), which was formed as the sole product from [Zn(tu)(4)]Cl-2. Thermo gravimetric analyses are reported for compounds 1-12. The compounds {[Zn(tu)(2)(mu-isophthalate)].H2O}(n) 3 and 12 lose their included water before 140degreesC, whereas the compounds {[Zn(tu)(2)(mu-maleate).-H2O}(n) 6 and 11 only lose their water molecules at higher temperatures with the onset of decomposition. This difference in behaviour can be related to the structural role of the water molecules. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).