Potentiometric and spectroscopic studies of the copper(II) complexes with some aminodiphosphonic acids in aqueous solution

Abstract

The stoichiometries and stability constants of the copper(II) complexes with seven aminodiphosphonates [R–N(CH 2PO 3H 2) 2, L] containing iminomethylenephosphonate moieties have been determined pH-metrically at 25°C and at an ionic strength of 0.20 mol dm −3 (KCl). The results suggest for L=1–6 only equimolar species: [Cu(H 2L), [Cu(HL), [CuL] and two hydroxo [CuH −1L] and [CuH −2L], in the pH range of 2–11.5, the only difference is the presence of an additional [Cu(H 3L)] species (∼15%) at low pH for N-3-picolyliminodi(methylenephosphonic) acid. For L=7 the model contains protonated and non-protonated 1:2 species. From the comparative analysis of the stability and the spectroscopic (UV–VIS and EPR) data it has been established that the ligands in [CuHL] and [CuL] are tridentate; the formation of two five-membered chelate rings leads to very stable complexes. The LMCT bands from O − (PO 3 2−) and N imino to Cu 2 are at 225–231 and 302–277 nm.