Ligand Exchange Kinetics of 2,2’-Bipyridine with Nitrilotriacetatonickelate(II)

Abstract

The kinetics of the ligand exchange reaction between 2,2’-bipyridine (bipy) and NiNTA^- was studied over the pH range 4.7 to 7.5 at 25.0 ⁰C and an ionic strength of 0.10 M by following the formation of Ni(bipy)₃ product at 307 nm. All reactions were run under pseudo-first order conditions with a [bipy]/[NiNTA^-] ratio of at least 20. The reaction is first-order with respect to each of NiNTA^- and to bipy. The reaction is also accelerated by hydrogen ion. The rate constant for the hydrogen ion unassisted addition of bipy to NiNTA^- is 0.671 M^-1 s^-1. The reaction is also first-order in hydrogen ion with a rate constant for the hydrogen ion assisted addition of bipy to NiNTA^- is 9.45 x 10⁴ M^-2 s^-1. A dissociative type mechanism accelerated by hydrogen ion is proposed. The work has significance by showing that NiEDDA and NiNTA, both aminopolyacrboxylate complexes react by the same mechanism.