Two novel cadmium coordination polymers bearing viologen-derived ligand: Structure and photochromism properties

Two novel cadmium viologen coordination polymers (CPs) {[Cd(BTC)(H2O)]·(Mebpy)}n (1) and {[Cd1.5(Mebpy)(BDC)1.5Cl]·(DMF)}n (2) were synthesized (Mebpy+ = N-methyl-4,4′-bipyridinium cation, DMF = N,N-Dimethylformamide, BTC3– = 1,3,5-benzenetricarboxylic acid anion and BDC4- = 1,4-dicarboxybenzene acid anion). The structures of two compounds were studied. For compound 1, Cd2+ is bridged with BTC3- to form a 3D structure, and Mebpy+ cations are present in the channel of compound 1. In compound 2, Cd2+, BDC2- and Mebpy+ form a 3D structure. And because of their different structures, they exhibit different properties. [Display omitted] •Two new coordination polymers (CPs) based on viologen ligands were synthesized.•1,3,5-benzenetricarboxylic acid and 1,4-dicarboxybenzene acid ligands form different 3D structures.•The photochromic properties of the compounds were explored. Two novel cadmium viologen coordination polymers (CPs) {[Cd(BTC)(H2O)]·(Mebpy)}n (1) and {[Cd1.5(Mebpy)(BDC)1.5Cl]·(DMF)}n (2) (Mebpy+ = N-methyl-4,4′-bipyridinium cation, DMF = N,N-Dimethylformamide) were prepared in the reaction of CdCl2 with different aromatic carboxylic acid ligands such as 1,3,5-benzenetricarboxylic acid (H3BTC) or 1,4-dicarboxybenzene acid (H2BDC) under hydrothermal conditions in the presence of N-carboxymethyl-4,4′-bipyridinium chloride (CEbpy·Cl). Single-crystal structure analysis revealed that the Cd(II) ions are bridged by BTC3- anions to form a 3D structure with the Mebpy+ cations occupying channel pores in compound 1, while the metal ions are bridged by BDC2- and Cl- anions to form a 3D structure with Mebpy+ cations in compound 2. Interestingly, it has been found that the structure of the two compounds depends on aromatic carboxylic acid ligands. Compounds 1 and 2 exhibit photochromic behavior under xenon lamp irradiation, accompanied by visible color changes from original color to blue.