Syntheses, structures, luminescent and photocatalytic properties of various polymers based on a “V”-shaped dicarboxylic acid

Abstract

Solvothermal reactions of “V”-shaped 3,5-di(4′-carboxyl-phenyl)benzene acid (H₂dpb), and Cd(II)/Zn(II) salts in the presence of four ancillary bridging imidazole linkers afford four novel luminescent coordination polymers (LCPs), namely, {[Cd(dpb)₂(bimb)₂]·0.5H₂O}_n (1), [Cd(dpb)(tib)]_n (2), [Zn(Hdpb)₂(4,4′-bibp)]_n (3) and [Cd(dpb)(1,3-bitl)]_n (4), (bimb = 1,4-bis(imidazol-1-ylmethyl)benzene, tib = 1,3,5-tris(1-imidazolyl) benzene, 4,4′-bibp = 4,4′-bis(imidazol-1-yl)biphenyl and 1,3-bitl = 1,3-bis(1-imidazoly)toluene). Then complexes 1–4 are characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis shows that complex 1 shows an unprecedented 3-nodal (2,2,4)-connected 2D + 2D → 3D two-fold interpenetration framework with the Schläfli symbol (12⁵·16)(12)². Complexes 2 and 3 show a 2D layer structure and 1D zigzag chain, which are further assembled into a 3D supramolecular structure by π⋯π interactions and H-bonds, respectively. While complex 4 displays a 3-nodal (2,2,8)-connected network with a –ABAB– fashion. The luminescent recognition properties of polymers 1–4 to metal cations and anions have also been explored systematically. The results demonstrate that 2 and 3 display highly sensitive and selective luminescence sensing towards Fe³⁺ ions, and 4 displays highly sensitive and selective luminescence sensing towards Cu²⁺ ions. 1–4 can work as highly sensitive sensors to Cr₂O₇²⁻ by luminescence quenching. Moreover, the photocatalytic properties of four Cd(II)/Zn(II) compounds (complex 1–4) have also been investigated.