The influence of hydrogen bonding on the structure of zinc co-ordination polymers

The compounds [Zn(tu)(2)(mu -fum)] 2 (tu=thiourea, fum=fumarate), [Zn(tu)(2)(mu -mal)] 3 (mal=malonate), [Zn(tu)(2)(mu -ipht)].H2O 4 (ipht=isophthalate), [Zn(tu)(2)(mu -citr)] 5 (citr=citraconate), [Zn(tu)(2)(mu -pht)] 6 (pht=phthalate), [Zn(tu)(2)(mu -male)].H2O 7 (male=maleate) and [Zn(tu)(2)(mu -hpht)](2) 8 (hpht=homophthalate) have all been prepared from the reaction of [ZnCl2(tu)(4)] with the appropriate sodium dicarboxylate. Crystal structure determinations of the seven compounds demonstrate that in 2-7 bridging dicarboxylates link the zinc centres into polymeric chains, whereas in 8 bridging homophthalates lead to discrete dimers. Where permitted by the relative orientations of the carboxylates, the chains are linked together by pairs of N-H . . .O hydrogen bonds between thiourea NH groups and carboxylate oxygen atoms in a hydrogen bond donor-donor acceptor-acceptor (DD:AA) arrangement. The hydrogen bonding patterns in the structure of 2 are very similar to those previously observed in [NEt4](2)[fum]. 2tu, suggesting that incorporation of zinc has little effect on the gross structure. The supramolecular structures of 5 and 6 are very similar to each other, and also to that of the previously reported compound [Zn(tu)(2)(mu -male)], which reflects the similar dispositions of the carboxylate groups. In contrast, the structure of 7 is very different, illustrating the dramatic effects that inclusion of solvent can have on the supramolecular structure.