Zinc dicarboxylate polymers and dimers: thiourea substitution as a tool in supramolecular synthesis

The reactions of the zinc thiourea complexes [Zn{SC(NHR)(NHR)}4]Cl2(L =L^1, R = H, R= Me; L =L^2, R = Me, R= Me) with a range of dicarboxylates have been investigated. From these reactions eleven products -[Zn(L1)2((mu)-terephthalate)]n, [Zn(L1)2((mu)fumarate)]n, {[Zn(L^1)2((mu)-isophthalate)]·H2O}n, [Zn(L^1)2((mu)-1,3-phenylenediacetate)]n, [Zn(L^1)2((mu)-phthalate)]2·4H2O, {[Zn (L^2)2((mu)-terephthlate)]·0.5H2O}n, [Zn(L^2)2((mu)-fumarate)]n, [Zn(L^2)2((mu)-isophthalate)]2·2H2O, [Zn(L^2)2((mu)-phthalate)]n, [Zn(L^2)2((mu)-maleate)]2·2H2O and [Zn(L^2)2((mu)-citraconate)]2·2H2O - have been crystallographically characterised. The structural characterisation of these compounds demonstrates that by increasing the number of methyl substituents on the thiourea ligand, the likelihood of forming a dimer as opposed to a coordination polymer also increases. Moreover, dimer formation is only favoured for nonlinear dicarboxylates - those in which the angle between the carboxylate groups is less than 180°.