Two new zinc(II) coordination polymers based on asymmetric tetracarboxylic acid for fluorescent sensing

Abstract

Two new luminescent zinc coordination polymers (CPs), [Zn(H2bptc)(2,2′-bipy)(H2O)]·3H2O (1) and [Zn2(bptc)(H2O)]·(4,4′-bipy)0.5 (2) (H4bptc=2,4,4′,6-biphenyl tetracarboxylic acid, 2,2′-bipy=2,2′-bipyridyl, 4,4′-bipy=4,4′-bipyridyl), have been solvothermally synthesized using zinc nitrate and asymmetric 2,4,4′,6-H4bptc ligand in the presence of auxiliary ligands. It is noted that H4bptc ligand exhibits two different coordination modes in these two CPs, constructing disparate architectures by bridging the different building units. CP 1 shows an infinite zigzag ribbon constructed from ZnO2(H2O)(2,2′-bipy) units and bridging H2bptc2− ligands. CP 2 displays a complicated 3D framework with 1D oval channels that built up from binuclear [Zn2(COO)3] second building units (SBUs) and bptc4− ligands. Moreover, they both present excellent sensing of metal ions and nitro explosives, especially for Fe3+ ion and 2,4,6-trinitrophenol (TNP). The KSV values of Fe3+ ion and TNP are 2.581×104 and 1.26×105L·mol−1 for 1, 2.826×104 and 3.422×105L·mol−1 for 2, respectively. The fluorescence quenching mechanism of 1 and 2 caused by TNP is ascribed to electron transfer and resonance energy transfer, while caused by Fe3+ may due to resonance energy transfer.