Stabilities and coordination modes of glycinephosphonic acid in copper(II) heteroligand complexes with ethylenediamine, diethylenetriamine or N,N,N′,N′,N″-pentamethyldiethylene triamine in aqueous solution

Solution equilibrium studies on the Cu(II)-polyamine-(aminomethyl)phosphonic acid (glycinephosphonic acid) ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N′,N″-pentamethyldiethylenetriamine (Me5dien)) have been performed by pH-potentiometry, UV–vis spectrophotometry and EPR methods. The obtained results suggest the formation of the heteroligand complexes with [Cu(A)(Gly(P))] stoichiometry in all studied systems. Additionally, in the systems with dien the protonated [Cu(dien)(H–Gly(P))]+ species also exists in acid solution and in the system with en the [Cu(en)(Gly(P))H-1]− species is formed in the basic solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(Gly(P))] species, the geometry slightly deviated from square pyramidal for the [Cu(dien)(Gly(P))] complex and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me5dien)(Gly(P))] species. The coordination modes in these heteroligand complexes are discussed.