Transition metal complexes with thiosemicarbazide-based ligands. Part L. Synthesis, physicochemical properties and crystal structures of Co(II) complexes with acetone S-methylisothiosemicarbazone

In this paper, we report the synthesis of three novel Co(II) complexes with acetone S-methylisothiosemicarbazone (L), (CH3)2C2N1–N2H–C1(SCH3)N3H. The complexes are characterized by IR spectroscopy and magnetic measurements while in the case of [CoL2Cl]I (1) and [CoLBr2] (2) the crystal structures have been determined by X-ray diffractometry. In both complexes the bidentate L ligand is coordinated in its imido form. In contrast to the other isothiosemicarbazide-based ligands, the molecule of L contains a localized double bond between the carbonyl and isothiosemicarbazide moieties (C2N1). The coordination polyhedron of 1 is best described as a distorted trigonal bipyramid. In the aim of a structural comparison, the analysis of similar five-coordinate bis(bidentate)–Co(II) and bis(bidentate)–Co(III) complexes containing two five-membered chelates has been carried out. The results suggest that if there is no steric hindrance between the ligands in the basal plane these complexes prefer a square-pyramidal geometry. The trigonal bipyramidal geometry of 1 is attributed to the steric interaction of L molecules caused by their favorable planarity. In complex 2 Co(II) exhibits a distorted tetrahedral geometry. The deformation of the coordination polyhedron is mainly attributed to the small bite angle of L. The similar position of the IR absorption bands in the spectra of 1 and 3 suggest their similar structural features. The values of the effective magnetic moments (μeff) per cobalt (II) for the three complexes are slightly higher than the values expected for the spin-only S = 3/2 systems.

The analyses of the geometries of five-coordinated bis(bidentate)–Co complexes containing five-membered chelate rings suggest that if there is no steric hindrance between the ligands in the basal plane complexes rather adopt square-pyramidal than trigonal-bipyramidal ligand arrangement.Figure optionsDownload as PowerPoint slide