Synthesis, structures and fluorescent properties of two cadmium(II) coordination polymers based on bis(benzimidazole) and different anions

Abstract

Two new Cd(II) coordination polymers (CPs), {[Cd(BBM)Cl2]·CH3OH}n (1) and [Cd2(BBM)2(isophthalate)2]n (2) (BBM = 2,2-(1,4-butanediyl)bis-1,3- benzimidazole), have been obtained from hydrothermal method and characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV-Vis spectra. The CP 1 displays a one-dimensional (1D) square wave chain structure connected by BBM ligands, whereas CP 2 is a 2D layer network. The structure analysis revealed that the selection of anions with different coordination modes realizes the control of the structure of the cadmium coordination polymer. Weak hydrogen bonds and π···π interactions are the major driving forces in the crystal packing of the two coordination polymers. Hirshfeld surface analysis reveals detailed scrutiny of intermolecular interactions experienced by each complex. In addition, the fluorescence properties of the ligands and CPs 1-2 in the solid-state were studied. The fluorescence peaks of the two Cd(II) CPs were weakened compared to the free ligands, which is attributed to ligand-centered fluorescence. The partial quenching of the aggregates may be due to the π···π stacking and heavy atom effect.