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

The stoichiometries and stability constants of the copper(II) complexes with seven amino-diphosphonates [R=N(CH2PO3H2)(2), L] containing iminomethylenephosphonate moieties have been determined pH-metrically at 25 degrees C and at an ionic strength of 0.20 mol dm(-3) (KCl). The results suggest for L = 1-6 only equimolar species: [Cu(H2L), [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(H3L)] species (similar to 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- (PO32-) and N-imino to Cu2+ are at 225-231 and 302-277 nm. (C) 1998 Elsevier Science Ltd. All rights reserved.