63658-44-6Relevant articles and documents
Complexation of o-phenylenediaminetetraacetic acid with some bivalent first-row transition-metal ions in aqueous solution
Nakasuka, Noriyuki,Kunimatsu, Mihoko,Matsumura, Kazunori,Tanaka, Motoharu
, p. 10 - 15 (2008/10/08)
Potentiometric and spectrophotometric studies have been carried out on the complexation of o-phenylenediamine-N,N,N′,N′-tetraacetic acid (PhDTA, H4L) with some transition-metal ions in aqueous solution at 25°C and at an ionic strength of 1 M (NaClO4). The studied metal ions include manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II). The usual pH titration method gave satisfactory results for the formation constants KML for manganese(II) and iron(II), but this was not the case for the other transition metals, whose complexes do not dissociate to an appreciable extent even at pH as low as 2. Therefore copper-selective and mercury electrodes were used to monitor free metal ion concentration in a ligand buffer containing an excess of a second metal ion. Spectrophotometric measurements resulted in an equilibrium constant for a relevant exchange reaction, from which KML was also obtained. Reduced basicity of the nitrogen atom in PhDTA is reflected in the formation constants of its complexes, which are lower than those of the corresponding EDTA and CyDTA complexes. However, the conditional formation constants of PhDTA complexes become the highest when these complexes are reacted in the acid region. This is due to the lower basicity of the ligand and the formation of diprotonated PhDTA complexes. The logarithmic formation constants of PhDTA complexes are linearly related with those of CyDTA complexes.
