Metal−Organic Coordination Architectures with Thiazole-Spaced Pyridinecarboxylates: Conformational Polymorphism, Structural Adjustment, and Ligand Flexibility

Abstract

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 NiII 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 CdII 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.