Constructions and properties of zinc coordination polymers based on 3,5-di(4H-1,2,4-triazol-4-yl) benzoic acid with different polycarboxylic acids as a secondary ligand

Five zinc coordination polymers, namely {[Zn(L)(NO3)]·(H2O)}n (1), {Zn2(L)2(p-BDC)}n (2), {[Zn2(H2O)2(L)(1,3,5-BTC)]·H2O}n (3), {[Zn2(L)2(H2BTEC)]·2H2O}n (4) and {[Zn3(H2O)4(L)2(BTEC)]·6(H2O)}n (5), {HL = 3,5-di(4H-1,2,4-triazol-4-yl)benzoic acid, H2p-BDC = 1,4-benzenedicarboxylic, 1,3,5-H3BTC = 1,3,5-benzenetricarboxylic acid, H4BTEC = 1,2,4,5-benzenetetracarboxylic acid}, were synthesized under solvothermal conditions. Single-crystal X-ray analyses show that complex 1 exhibits two-dimensional (2D) double-layered 3,4L88 nets with π–π interactions. Complexes 2, 3 and 4 display the same 2D topological structures as that of complex 1, except for the further formation of different 2D → 3D supramolecular structures in 2 and 4. Complex 2, with a deprotonated [p-BDA]2− ligand, forms interpenetrated structures with the (62·84)(66)4 topology built by π–π interactions, whereas complex 4, built by partially deprotonated [H2BTEC]2− ligands, forms a similar interpenetrated three-dimensional (3D) framework with a point symbol of (66). When the mixed ligand was changed into 1,3,5-H3BTC in 3, the coordination mode of one Zn(II) atom is trigonal–bipyramidal as opposed to tetrahedral in 1, 2 and 4, and each [L]− anion acts as a tetradentate ligand linking four Zn(II) ions instead of a tridentate ligand, generating a 3,4,4,5-connected (63)(66)2(69·8) framework in 3. In complex 5, the completely deprotonated H4BTEC ligand connects four Zn(II) ions as a tetracarboxylate ligand to produce a 2-fold interpenetrated three-dimensional (3D) framework with a point symbol of (4·6·72·82)2(42·72·82)(62·73·8)2. The five complexes have also been characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction and thermogravimetry measurements. It was also found that the fluorescence of complexes 1–5 could be quenched by nitrobenzene (NB), indicating their potential application as sensory materials.