Syntheses, Structures and Optical Band Gaps of Three Zn(II)/Co(II) Coordination Polymers

Three new coordination polymers with formulas [Zn(L1)(L2)(0.5)Cl](n), (1), [Co(L1)(L2)(0.5)Cl](n), (2) and ([Zn(L1) (L3)]ClO4 center dot 1.7H(2)O)(n) (3) have been prepared via the combination of zwitterionic carboxylic ligand with Zn(II) and Co (II) salts under the participation of two bridging imidazole-based isomers, where Ll, L2 and L3 are 4-carboxy-1-(4-carboxybenzy1)-pyridinium, 1, 4-bis(imidazole-1-ylmethyl)benzene and 1, 3-bis(imidazole-1-ylmethyl)benzene, respectively. Complexes 1 and 2 are isostructural and feature an undulated 2D herringbone layer structure with (6,3) topology, exhibiting a rare 2D -> 3D inclined polycatenated structure. Compared with 1 and 2, complex 3 displays 1D catenated chain structure, which are further assembled into 2D layer via abundant pi-pi interactions. It is noteworthy that 1 similar to 3 can all be considered as consisting of 1D [M(Ll)](n) chains and bridging bis-imidazole-based ligands. For 1 and 2, the 1D [M(Ll)](n) chains take helical form and bridging L2 ligands adopting Z -shape. In contrast, the 1D [M(L1)],. chains in 3 exhibit zigzag form and bridging L3 ligands having C -configuration. The results reveal that different N -donor ancillary ligands and anions have a subtle effect on the final structures. The study of optical band gaps showed that the band gaps of 1-3 were 2.96, 1.72 and 3.16 eV, respectively, which indicates that 1 similar to 3 have properties of potential wide -band -gap semiconductors. CCDC: 1973985, 1; 1973986, 2; 1973987, 3.