Mode of Bonding and Isomerism in Mixed Cu(II) Thiocyanate Diamine Ligand Complexes

Abstract

The reactions of excess thiocyanate with Cu(II) ions in the presence of the chelate ligand 1,3-diaminopropane (dp) were reinvestigated. The reaction in ethanol yielded successively brown, violet and blue complexes. The above order of isolation corresponds to their respective decreasing molecular masses and increasing solubilities. The use of vibrational (infra-red) and electronic (ultra-violet/visible) spectra in elucidating the structure and mode of coordination of the thiocyanate groups was discussed. The possibility of linkage isomerism and intermolecular H-bonding were also examined. The infra-red spectrum of the brown complex [Cu2(dp)(SCN)4] showed bands in the ?CN region strongly suggesting a dimeric species. Further evidence for the dimeric structure was provided by the insolubility of the complex in most of the common solvents but it dissolved readily in pyridine which is a donor solvent capable to cleave catenating bridges in polymeric species.