Structure, solution equilibria and magnetic properties of copper(II) complexes with new sulfurated triazoline derivatives of α-amino acids

Two new sulfurated triazoline ligands have been synthesized by functionalization of glycine and l-alanine (HL1 and HL2, respectively) at the carboxylate site with retention of chirality in the latter case. The ligands and their copper(II) complexes have been characterized by spectroscopic methods and their structures were determined by X-ray diffraction. The compound [Cu(H2L2)2](H5O2)(SO4)2(HSO4) presents a very disordered structure with regard to the anionic counterion and a very unusual elongated crystal cell. In all the complexes the ligands are (N,S) coordinated to copper(II), while the amino groups remain protonated and uncoordinated. The ligands have also been studied in solution and their dissociation constants were determined both by potentiometry and 1H NMR titrations. Potentiometric studies on the complex [Cu(H2L2)2](H5O2)(SO4)2(HSO4) were performed to determine the dissociation constants of the ligand once coordinated to the metal. The complex [CuCl2(H2L1)]Cl was studied also by magnetic susceptibility measurements, showing an interesting antiferromagnetic behavior at low temperature which has been interpreted on the basis of its crystal packing.