Reactions of 1,3,5-benzenetricarboxylic acid with Zn(II) ion in the presence of added amines: Isolation; structure determination of zinc coordination polymers with tetrahedral; 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 [Zn₃(BTC)₂(DMP)₆.2.5H₂O] (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 [Zn₃(BTC)₂.12H₂O] (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)₄Zn₂(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 π-π interactions to form a 3-D network. Compound 2 is made up of a zig-zag chain of alternating BTC^3- 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.