Metal-organic coordination architectures with thiazole-spaced pyridinecarboxylates: Conformational polymorphism, structural adjustment, and ligand flexibility

Two derivative ligands of nicotinic or isonicotinic acid, namely, 2-(3-pyridyl)-4-methylthiazole-5-carboxylic acid (Hpmtca) and 2-(4-pyridyl)thiazole-4-carboxylic acid (Hptca), have been employed to assemble with a variety of divalent metal ions, leading to the generation of diverse metal-organic supramolecular architectures in different dimensions. Among them, complexes 1a and 1b, [Ni(pmtca)(2)(H2O)(4)](n), present a pair of conformational polymorphs with different neutral layered arrays, which are obtained from similar reaction conditions with Ni-II salts of different sources. [Cu(pmtca)(2)(H2O)](n) (2) and [Zn(pmtca)(2)(H2O)](n) (3) are isostructural two-dimensional (2-D) corrugated coordination networks. These layered patterns adopt interdigitated three-dimensional (3-D) crystalline packing and are further consolidated by hydrogen bonding, while [Co(pmtca)(2)(CH3CH2OH)(2)](n) (4) shows a distinct one-dimensional (1-D) double chain structure. As for the Cd-II species, [Cd(pmtca)(2)(H2O)(2)](n) (5) comprises a similar layered framework as that in 1a, whereas the mononuclar complex [Cd(ptca)(2)(H2O)(4)] (6) displays a 3-D supramolecular network via multiple intermolecular hydrogen bonds. The ligand conformation is systematically investigated to further explore its relationship with the resultant crystalline architectures.