DOI: 10.14457/tu.the.2023.381
title: Synthesis, characterization, crystal structure and photoluminescence properties of new zinc (ii) and cadmium (ii) coordination polymers containing 4, 4′-bipyridine and benzoate

description: This research is focused on the design, synthesis, characterization, and properties of four new zinc(II) and cadmium(II) coordination polymers constructed by 4,4′-bipyridine (4,4′-bipy) and benzoate (benz) ligands. These new compounds namely [Zn3(4,4′-bipy)2(benz)4(fum)2]n (1), [Zn2(4,4′-bipy)2(benz)4]n (2), [Cd(4,4′-bipy)(benz)NO3]n (3) and [Cd3(4,4′-bipy)4(benz)6(H2O)2]n (4) (fum = fumaraldehyde) have been success-fully synthesized using a slow evaporation method with various synthetic conditions such as the mole ratio of reactants and pH effect of the solution. All compounds were obtained with the same reactants mole ratio of Zn(NO3)2⋅6H2O or Cd(NO3)2⋅4H2O : 4,4′-bipy : benzH with 1:1:1, at different pH values of 6.5, 6.0, 5.0, and 7.0 for compounds 1-4, respectively. All synthesized compounds were characterized using ATR-FTIR, elemental analysis, TGA and PXRD techniques. The crystal structures of all compounds have been determined by using single-crystal X-ray diffraction technique. The various topologies of these compounds revealed distinct and fascinating structures. Compound 1 exhibits a three-dimensional structure with pcu topology, compound 2 displays a one-dimensional zigzag-like chain, compound 3 demonstrates a one-dimensional ladder-like chain and compound 4 presents a one-dimensional ladder-like net. All compounds exhibited high purity and repeatability, as confirmed by the PXRD patterns. The TGA technique was performed to verify the thermal stability for all compounds, these results show that these compounds were stable up to 200, 175, 250 and 285.5 °C for compounds 1-4, respectively. The solid-state photoluminescence (PL) properties of all compounds were studied, and their PL emission exhibited at the maximum wavelengths of 375, 370, 360, and 370 nm for compounds 1-4, respectively. Interestingly, compound 1 showed the highest emission intensity compared to the rest compounds and free ligands. All compounds were studied the PL sensing properties for small organic solvents, nitroaromatic compounds (NACs), metal ions and anions by investigation of the PL quenching effect. For the small organic molecule sensing properties, all compounds present selective sensing for acetone in acetonitrile, with the limit of detection (LOD) of 1.89×10–3, 7.61×10–3, 4.90×10–2, and 8.20×10–2 v/v% for compounds 1-4, respectively. For the NACs sensing properties, it was found that compounds 1, 3, and 4 exhibit non-specific detection for NACs. Regarding to only compound 1 shows the high water stability in water for 1 day under stirring, it was examined as a sensing material for metal ions and anions. Compound 1 exhibited selective sensing for ferric ions (Fe3+), with LOD of 1.28×10-6 mol/L and showed sensing for CrO42−, Cr2O72− and MnO4− anions. Moreover, compound 1 is stable and reusable for at least ten and seven cycles toward acetone and Fe3+ ion, respectively. While, compounds 3 and 4 can be also reused for detection of acetone at least seven and six cycles, respectively. The PL sensing properties of these compounds are identified as fluorescence resonance energy transfer (FRET) mechanism for underlying process for the quenching effect.