Self-assembly of Zn/Cd-coordination polymers based on 3,3′,4,4′-biphenyltetracarboxylic acid and N-donor ligands and luminescence sensing of Fe3+ ions

Two new d10 configuration coordination polymers based on H4bpta (H4bpta = 3,3′,4,4′-biphenyltetracarboxylic acid) and N-donor ligands, namely [Zn2(1,3-bimb)2(bpta)]n (1) and [Cd2(1,3-bimb)(bpta)(H2O)]n·0.5nH2O (2) (1,3-bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene), have been obtained under solvothermal conditions. The bpta4− ligands show various coordination modes due to the different radiuses of metal ions in structures 1 and 2. Compound 1 is a 3D network built up of 4-connected bpta4− and 1,3-bimb ligands bonding with Zn2+ ions in monodentate modes. Compound 2 also exhibits a 3D structure formed through H4bpta and 1,3-bimb linkers cross-linking the [Cd3(µ-COO)2]4+ secondary-building units (SBUs), in which the carboxylate groups can adopt three coordination modes with chelating, μ2-O, and syn–syn bridging types. In addition, two different 1D zigzag chains (–Zn–(1,3-bimb)–Zn– for 1, and –Cd–(1,3-bimb)–Cd–(μ-O)–Cd– for 2) are formed by the 1,3-bimb ligands with trans-conformation linking metal ions. The fluorescence properties of the free ligands, 1 and 2 have been investigated carefully, and compound 2 displays highly selective and sensitive sensing for Fe3+ ions in DMF solution.