Coordination chemistry of benzene polycarboxylic acids - 2. Reactions of 1,3,5-benzenetricarboxylic acid with Zn(II) ion in the presence of added amines: Isolation and structure determination of zinc coordination polymers with tetrahedral and octahedral zinc centres

Abstract

The formation of two metal-organic coordination polymers and an organic supramolecular network based on 1,3,5-benzenetricarboxylic acid (H3BTC) is reported. While [Zn-3(BTC)(2)(DMP)(6)(.)2.5H(2)O] (1) is formed by the addition of zinc acetate and 3,5-dimethylpyrazole (DMP) to H3BTC, the addition of zinc acetate to 4-aminopyridine and H3BTC results in previously reported [Zn-3(BTC)(2)(.)12H(2)O] (2). On the other hand, the interaction of H3BTC with ZnSO4 in the presence of piperazine (PIP) leads to the formation of [H2BTC](2)[H2PIP] (3) as soluble single crystals in addition to an insoluble zinc-BTC-piperazine complex with unknown composition. The solid-state structures as determined by single crystal X-ray diffraction studies reveal that compounds 1-3 form 3-D polymeric networks with the aid of extensive hydrogen bonding. In 1, the adjacent dimeric units of [(DMP)(4)Zn-2(BTC)(2)] are bridged by [Zn(DMP)(2)] units to form a polymeric chain structure. These chains are in turn linked to each other through hydrogen bonding to form a 2-D sheet network. The 2-D sheets are held together by weak pi-pi interactions to form a 3-D network. Compound 2 is made up of a zig-zag chain of alternating BTC3- ion and Zn(H2O)(4) octahedral units. These chains are held together by numerous hydrogen bonding interactions resulting in a porous solid. The supramolecular assembly in 3 can be described as a host-guest complex in which the hydrogen bonded [H2BTC-](n) network hosts the piperazinium cations.