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

Abstract

The reactions of the zinc thiourea complexes [Zn{SC(NHR)(NHR′)}₄]Cl₂ (L = L¹, R = H, R′ = Me; L = L², R = Me, R′ = Me) with a range of dicarboxylates have been investigated. From these reactions eleven products – [Zn(L¹)₂(μ-terephthalate)]_n, [Zn(L¹)₂(μ-fumarate)]_n, {[Zn(L¹)₂(μ-isophthalate)]·H₂O}_n, [Zn(L¹)₂(μ-1,3-phenylenediacetate)]_n, [Zn(L¹)₂(μ-phthalate)]₂·4H₂O, {[Zn(L²)₂(μ-terephthlate)]·0.5H₂O}_n, [Zn(L²)₂(μ-fumarate)]_n, [Zn(L²)₂(μ-isophthalate)]₂·2H₂O, [Zn(L²)₂(μ-phthalate)]_n, [Zn(L²)₂(μ-maleate)]₂·2H₂O and [Zn(L²)₂(μ-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 non-linear dicarboxylates – those in which the angle between the carboxylate groups is less than 180°.