A Comparative Study of Stabilities and Coordination Modes of β-Alaninephosphonic Acid in Copper(II) Heteroligand Complexes with Ethylenediamine Diethylenetriamine or NNN′N′N″-Pentamethyldiethylene Triamine in Aqueous Solution

摘要

Solution equilibrium studies on Cu²⁺–L1–L2 ternary systems have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods {where L1 corresponds to a polyamine such as ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N′,N″-pentamethyldiethylenetriamine (Me5dien)} and L2 denotes 2-aminoethylphosphonic acid (β-alaninephosphonic acid)}. The results suggest the formation of heteroligand complexes with [Cu(L1)(β-Ala(P))] stoichiometry in all of the studied systems. Additionally, in the system with en, [Cu(en)(β-Ala(P))H−1]⁻ is formed in basic solutions. Our spectroscopic results indicate tetragonal geometry for the [Cu(en)(β-Ala(P))] species, a geometry slightly deviated from square pyramidal for the [Cu(dien)(β-Ala(P))] complex, and somewhat stronger geometry distortion was present for the [Cu(Me5dien)(β-Ala(P))] complex. The coordination modes in these heteroligand complexes are discussed.