Versatile frameworks constructed from divalent metals with 4,4′-methylenedibenzoic acid and imidazole derivative ligands: Syntheses, crystal structures and physical properties

Seven coordination polymers, namely, [Zn(DBA)(Hpyim)]n·nH2O (1), [Cd(DBA)(Hpyim)]n (2), [Zn(DBA)(bix)]n·2nH2O (3), [Co(DBA)(bix)]n (4), [Ni(DBA)(bix)]n (5), [Co(DBA)(mbix)]n (6), and [Ni(DBA)(mbix)(H2O)2]n·nH2O (7), where H2DBA=4,4′-methylenedibenzoic acid, Hpyim=2-(2-pyridyl)imidazole, bix=1,4-bis(imidazol-1-ylmethyl) benzene and mbix=1,3-bis(imidazol-1-yl-methyl) benzene, were synthesized. Complex 1 is a one-dimensional (1D) infinite chain. Complex 2 has a two-dimensional (2D) 4-connected (4,4) network based on dinuclear units. Complex 3 features a 2D sheet constructed from mononuclear center. Complexes 4 and 5 exhibit similar 2D layers, which are further linked into 3D supramolecular frameworks through π–π interactions. Complex 6 possesses a 3D 5-fold interpenetrating diamond framework, while complex 7 shows a 1D double-strand chain. The results indicate that the coordination modes of DBA, auxiliary ligands and metal ions play important roles in the formation of the final framework. Moreover, the luminescent properties of 1–3 and nonlinear optical and ferroelectric properties of 1 were also investigated.