Two complexes of a thiosemicarbazone ligand, namely N-(2-hydroxyethyl)-2-(thiophene-2-ylmethylene)- hydrazinecarbothioamide (HL), have been synthesized. The complexes have been characterized by physico-chemical and spectroscopic methods. The crystal and molecular structures of [CoL3]2MeOH (1) and [NiL2] (2) have been determined by X-ray diffraction studies. For both complexes, the metal is coordinated through the sulfur and azomethine nitrogen atoms of the thiosemicarbazone. The ligand exists in its thiolate tautomeric form, and the central Co(III) and Ni(II) atoms have distorted octahedral and square planar geometries, respectively, with five-membered chelate rings formed by the ligand. The lattice of 1 shows infinite oxygen donor/acceptor hydrogen bonds in the ab plane and weak interactions between rings along the c axis, respectively, giving a supramolecular network. The molecular units in 2 are linked together by hydrogen bonds between the hydroxyl oxygen and hydrazone N proton, giving rise to an infinite ribbon extended along the c-axis. These chains are connected by N3–H3O1 interactions that form a sheet within the ac plane.

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