A series of novel Co(II)-based MOFs: syntheses, structural diversity, and various properties

Three novel cobalt metal-organic frameworks (Co-MOFs), namely, {[Co-3(L)(3)(bip)]center dot 2H(2)O}(n) (1), [Co(L)(bibp)(0.5)](n) (2) and [Co(L)(bbi)(0.5)](n) (3) (H2L = 3-(3,5-dicarboxylphenoxy)pyridine, bip = 3,5-bis(1-imidazoly)pyridine, bibp = 4,4 '-bis(imidazol-1-yl)biphenyl, bbi = 1,1 '-(1,4-butanediyl)bis(imidazole)) have been successfully synthesized by a solvothermal method. Various auxiliary second ligands and different solvents led to the diversity of three Co-MOFs. Topological analysis exemplified 7-nodal (3,3,4,4,4,5,5)-connected net for 1, (3,5)-connected binodal net for 2, and (3,4)-connected binodal net for 3. The ability of MOFs 1-3 to remove dyes has been explored and among them, 1 could remove congo red (CR) dye with efficiency, selectivity and maintain excellent performance in various mixed dyes. The evaluation parameters, including adsorption capacity, reusability, adsorption isotherms and adsorption thermodynamics have been performed to investigate the adsorption of MOF 1. A possible mechanism has been studied through infrared spectroscopy and XPS analysis, and the chemical actions (hydrogen bonds and pi-pi stacking interactions) contributed much to the adsorption process. According to cyclic voltammetry (CV) experiments, MOFs 1-3 exhibited potential electrocatalytic water oxidation performances. Direct-current (dc) magnetic susceptibility of 1-3 indicated the presence of dominant antiferromagnetic coupling, which revealed their potential values in information storage, processing and transmission.