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

Abstract

The compounds [Zn(tu)₂(μ-fum)] 2 (tu = thiourea, fum = fumarate), [Zn(tu)₂(μ-mal)] 3 (mal = malonate), [Zn(tu)₂(μ-ipht)]·H₂O 4 (ipht = isophthalate), [Zn(tu)₂(μ-citr)] 5 (citr = citraconate), [Zn(tu)₂(μ-pht)] 6 (pht = phthalate), [Zn(tu)₂(μ-male)]·H₂O 7 (male = maleate) and [Zn(tu)₂(μ-hpht)]₂8 (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(μ-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.