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

Two new Cd(II) coordination polymers (CPs), {[Cd(BBM)Cl-2]center dot CH3OH}(n) (1) and [Cd-2(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 pi...pi 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 pi center dot center dot center dot pi stacking and heavy atom effect. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Two new Cd(II) coordination polymers were prepared using a hydrothermal method and characterized as one-dimensional and two-dimensional structures. The control of the coordination polymer structure was achieved by the selection of anions with different coordination modes, with weak hydrogen bonds and π···π interactions being the major driving forces in crystal packing. Fluorescence properties study in the solid-state showed weakened fluorescence peaks for both ligands and coordination polymers, attributed to ligand-centered fluorescence and partial quenching caused by π···π stacking and heavy atom effects.