Solvent effect on the ligand exchange between bis(diethyldithiocarbamato)copper(II) and bis(diethyldiselenocarbamato)copper(II)

EPR study on the products of ligand exchange taking place on mixing bis(diethyldiseleno-carbamato)copper(II), Cu(dsc)2, and bis(diethyldithiocarbamato)copper(II), Cu(dtc)2, solutions is reported. EPR spectra monitored at room temperature for 1 month period reveal a stable equilibrium among the parents (chromophores CuS4 and CuSe4) and the obtained mixed-chelate Cu(dtc)(dsc) complex (chromophore CuS2Se2) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl4 and CHCl3, two new additional EPR spectra appear attributed to the mixed-chelate complexes with chromophores Cu(SSe3)S and Cu(S3Se)S. The intensities of all five EPR spectra slowly decrease with the time in CHCl3 after 1 month monitoring at room temperature, or one week at 60 °C whereas in CCl4 only the spectrum of Cu(dtc)2 remains at room temperature on keeping the sample solution for 1 week after mixing or 1 h at 60 °C. The reaction mechanism of formation of both additional complexes with chromophores Cu(SSe3) and Cu(S3Se) is discussed. It is assumed that the new mixed-chelates observed in CCl4 and CHCl3 are obtained in a reaction of Cu(dtc)(dsc) or Cu(dtc)2 with the ester of diselenocarbamic acid which is formed in a parallel reaction of Cu(dsc)2 with CCl4 or CHCl3.