Unexpected formation of cis-[(DMSO)2ClCuII(μ-Cl)2CuIICl(DMSO)2] in the reaction of trans-[CuCl2(DMSO)2] with the thiohydantoin type ligand

Abstract

In the reaction of well-known trans-[CuCl2(DMSO)2] complex with the polydentate thiohydantoin type ligand, 3-[(2-hydroxybenzylidene)amino]-2-thioxoimidazolidin-4-one [1], unexpected cis-[(DMSO)2ClCuII(μ-Cl)2CuIICl(DMSO)2] complex was formed predominantly as the final stable product, which structure was confirmed by single crystal X-ray crystallography (Fig. 1). Till now, only one procedure was reported, based on a specific preparation via decomposition of a tetranuclear [Cu4Cl8(DMSO)8(hmta)] complex. Starting ligand of thiohydantoin type is mostly recovered, while the minor amount is coordinated to Cu(II) ion. Coordination of the ligand is confirmed by different spectroscopic methods [3], but for the final elucidation of the structure of this minor product and the coordination mode the X-ray analysis is needed. As the cis-isomer could not be obtained by direct synthesis and in our case is not obtained by decomposition of another complex, our investigation is directed to resolving the mechanism of this reaction and the role of the presence of the starting ligand in the isomerization of trans-complex to cis-form by either experimental or theoretical methods.