Kinetics and mechanism of ligand substitution in binuclear nickel(II) and cobalt(II) complexes

✍ Scribed by Michael J. Hynes; Marie T. Doody

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 651 KB
• Volume: 27
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550270502

✦ Synopsis

The kinetics and mechanism of the removal of M2+ from bis-(heptane-2,4,6-trionato)M(II) [M = Ni, Co] by ethylenediminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), 1,2-cyclohexanediamine-N, N, N', N'tetraacetic acid (CyDTA), and ethylenebis(oxyethylenenitri1o)tetraacetic acid (EGTA) have been investigated using stopped-flow spectrophotometry in methanol-water at 25°C and ionic strength 0.1 mol dmp3 KNO3. The reactions were investigated at a number of different pHs.

An associative mechanism is proposed to account for the kinetic data. Although all the ligands have similar functional groups, their reactivity towards the parent complex is quite different. The pH dependence of the rate constants has been used to determine the relative reactivities of the various ligand species present. In the case of nitrilotriacetic acid, a nonlinear dependence on ligand concentration is observed, thus confirming the mechanism proposed.