Potentiometric and spectroscopic studies of the cobalt(II), nickel(II) andmanganese(II) complexes with some aminodiphosphonic acids in aqueous solution

The stoichiometries and stability constants of the manganese(II), cobalt(II ) and nickel(II) complexes with seven aminodiphosphonates [RN(CH2PO3H2)(2)L ] containing iminomethylenephosphonate moieties have been determined pH-met rically at 25 degreesC and at an ionic strength of 0.20 mol dm(-3) (KCL). T he results suggest for L=1-6 only equimolar species: [M(H2L)], [M(HL)](-), [ML](2-) and hydroxo [MH-1L](3-), in the pH range of 3-11.5, the only diffe rence is the presence of an additional [M(H3L)](+) species at low pH for N- 3-picolyliminodi(methylenephosphonic) acid. For L=7 the models contain prot onated and non-protonated 1:2 species. From the comparative analysis of the stability and the spectroscopic (UV-VIS) data it has been established that the ligands coordinate to the metal ions only by the phosphonate group(s) in a monodentate or bidentate manner. The LMCT bands from O-(PO32-) to Ni2 are at 222-211 nm. (C) 2000 Elsevier Science Ltd. All rights reserved.