Supramolecular architectures of cadmium(II) built of 2,2′-biimmidazole and bifunctional carboxylates: Syntheses, crystal structure and properties

A series of four new supramolecular complexes of cadmium(II), {[CdBr(H2biim)(PyCO2)(H2O)](H2O)}∞ (1) (H2biim = 2,2′-biimidazole, PyCO2 = isonicotinate), [Cd(H2biim)2(HBDC)2] (2) (H2BDC = terephthalic acid), [Cd(H2biim)2(H2O)2](BDC) (3) and [Cd(H2biim)2(H2O)2](PyCO2)2 · 4H2O (4) have been prepared and characterized by X-ray crystallography, IR, fluorescence spectra and thermogravimetric analysis. Compound 1 exhibits an infinite chain-like structure through bridging isonicotinate. Strong interchain hydrogen bonds between isonicotinate and H2biim result in the robust 2-D sheet structure, responsible for the insolubility. The similar hydrogen bonds between H2biim and the coordinated 1,4-bdc and complementary hydrogen bonds between monoprotonated bdc are responsible for the robust 2-D layered structure of 2 that is insoluble in aqueous solution. 1,4-Bdc becomes uncoordinated in the soluble complex 3, although it has hydrogen bonded 2-D structure as well.