Synthesis and characterizations of two bis(benzimidazole)-based cobaltous coordination polymers with high adsorption capacity for congo red dye

Two Co(II) coordination polymers, namely [Co(L1)(tp)]n (1) and [Co(L2)(Htp)(tp)0.5]n (2) (L1 = 1,3-bis(5,6-dimethylbenzimidazole)propane; L2 = 1,2-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene; tp = terephthalate) have been synthesized and structurally characterized by single crystal X-ray diffraction. In 1, the Co(II) centers are four-coordinated and lie in nearly perfect tetrahedron coordination environment. The 2D (4, 4) layer is formed by the bridging L1 and tp ligands, which further assembles into a 3D supramolecular framework by π–π stacking interactions. In 2, the Co atoms are in distorted trigonal–bipyramidal geometry and linked by tp ligands to generate a 1D linear chain. The adjacent chains are finally extended to a 2D supramolecular layer through hydrogen-bonding interactions. In addition, fluorescence and remarkable adsorption properties for congo red dye of complexes 1 and 2 have been investigated.