COMPLEX-FORMATION IN COPPER(II) TERNARY-SYSTEMS INVOLVING POLYAMINES AND DIAMINOCARBOXYLATES STUDIED BY POTENTIOMETRIC AND SPECTROSCOPIC TECHNIQUES

Potentiometric and spectroscopic methods were used to study complex fo rmation in ternary Cu(II) systems with the ligands en, tn, Put, dien, 2,3-tri, 3,3-tri, Spd, dapa and daba. Mixed complexes, Cu/diamine/tria mine, formed in aqueous solution are characterized by 5N-type coordina tion, with four atoms coordinating equatorially and one at an axial po sition. An exception is the complex Cu(Put)(3,3-tri) in which 4N coord ination was detected. A relatively low tendency to form mixed complexe s was found for Cu/triamine/triamine systems, where formation of only the Cu (dien)(Spd) compound was found. The complexing character of dab a molecules proves diversified and dependent on the type of the second ligand it forms the complex with. In Cu/daba/diamine compounds, coord ination of the 3N10 type (with a 1N10 fragment from daba) was observed . In the Cu/daba/triamine complexes one nitrogen atom of the diaminoca rboxylate is involved in coordination at an equatorial position and th e second at an axial position (5N coordination). A dapa ligand is not so diversified and its two amino groups coordinate equatorially (2N), yielding chromophore 4N in complexes with diamines (probably with weak interaction of an oxygen atom) and 5N with triamines. Spermidine also reveals different coordination properties, depending on the second li gand. In complexes with diamines, the interactions involve 3 nitrogen atoms from Spd but only two in complexes with triamines. Following the process of formation of mixed copper(II) complexes it was found that with increasing pH, in the triamine/diamine and triamine/diaminocarbox ylate systems, the anchoring ligand is the triamine, while in the diam ine/diaminocarboxylate systems, dapa or daba are first to react and on ly then does the diamine join the complex.