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

Abstract Two new luminescent zinc coordination polymers (CPs), [Zn(H 2 bptc)(2,2′-bipy)(H 2 O)]·3H 2 O ( 1 ) and [Zn 2 (bptc)(H 2 O)]·(4,4′-bipy) 0.5 ( 2 ) (H 4 bptc = 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-H 4 bptc ligand in the presence of auxiliary ligands. It is noted that H 4 bptc 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 ZnO 2 (H 2 O)(2,2′-bipy) units and bridging H 2 bptc 2− ligands. CP 2 displays a complicated 3D framework with 1D oval channels that built up from binuclear [Zn 2 (COO) 3 ] second building units (SBUs) and bptc 4− ligands. Moreover, they both present excellent sensing of metal ions and nitro explosives, especially for Fe 3+ ion and 2,4,6-trinitrophenol (TNP). The K SV values of Fe 3+ ion and TNP are 2.581 × 10 4 and 1.26 × 10 5  L·mol −1 for 1 , 2.826 × 10 4 and 3.422 × 10 5  L·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 Fe 3+ may due to resonance energy transfer.