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 (H 2 O) 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 (H 2 O)] n ( 2 ) and [Zn(pmtca) 2 (H 2 O)] 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 (CH 3 CH 2 OH) 2 ] n ( 4 ) shows a distinct one-dimensional (1-D) double chain structure. As for the Cd II species, [Cd(pmtca) 2 (H 2 O) 2 ] n ( 5 ) comprises a similar layered framework as that in 1a, whereas the mononuclar complex [Cd(ptca) 2 (H 2 O) 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.