Polymorphism in metal complexes of thiazole-4-carboxylic acid

Abstract

Five new molecular complexes of chemical formula [M(4-tza)2(H2O)2] (M = Co, Ni, or Cu) and a complex of [Cu(4-tza)2]·4H2O using thiazole-4-carboxylic acid (4-tza) as the ligand have been successfully synthesized and structurally characterized by single crystal X-ray diffraction. Two district polymorphs (α and β) are found for both [Co(4-tza)2(H2O)2] and [Ni(4-tza)2(H2O)2]. The effects of solvent composition and temperature on the formation of these polymorphs have been investigated and phase behaviour of the polymorphs was studied through X-ray powder diffraction. Unlike the complexes of Co and Ni, [Cu(4-tza)2(H2O)2] does not display polymorphism but exhibits irreversible structural transformation from [Cu(4-tza)2(H2O)2] to the dehydrated form, [Cu(4-tza)2], upon heating.