Formation studies of binary and ternary complexes of copper(II) with an oxazol derivative of nicotinic acid and some amino acids

Binary and ternary complexes of copper(II) with the 2-(benzo[d]oxazol-2-yl)nicotinic acid (Ligand HL) and the amino acids Glycine (HGly, HB), Proline (HPro, HB), α-Alanine (Hα-Ala, HB), β-Alanine (Hβ-Ala, HB) were studied in aqueous solution at 25 °C, using 1.0 mol · dm− 3 KNO3 as the ionic medium. The types of complexes formed and their overall stability constants were established on the basis of the computer analysis of the potentiometric data, using a version of the program LETAGROP. It was inferred that the aromatic oxazol Ligand L− 1 acts as a primary ligand in the ternary complexes, while the oxygen and nitrogen donor-containing amino acids are the secondary ligands. The analysis showed the formation of five complexes: [Cu(L)(HB)]+, Cu(L)(B), [Cu(L)(B)(OH)]−, [Cu(L)2(B)]− and [Cu(L)(B)2]− in the Cu(II)-L−-Gly and Cu(II)-L− -βAla systems, for the Cu(II)-L−-Pro system, the complexes [Cu(L)(HB)]+, Cu(L)(B), [Cu(L)(B)(OH)]− and [Cu(L)(B)2]− were detected and, finally, in the Cu(II)- L− - αAla system, only the complexes [Cu(L)(HB)]+, Cu(L)(B) and [Cu(L)(B)(OH)]− were observed. The concentration distributions of various species formed in aqueous solution were also evaluated as a function of pH.