Ligand substitution reactions of the (nitrilotriacetato)copper(II) complex (CuNTA−) with simple mono- and bidentate ligands (L) have been investigated by making use of the temperature-jump relaxation technique. At 25 °C, the forward rate constants for reaction CuNTA− + L = CuNTA(L)− are as follows: L = NH3, 1.5 × 108 M−1 s−1; L = CH3NH2, 3.4 × 107 M−1 s−1; L = glycinate, 1.1 × 108 M−1 s−1; L = α-alaninate, 4.9 × 107 M−1 s−1; L = β-alaninate, 3.8 × 107 M−1 s−1; L = 2,2′-bipyridine, 1.2 × 106 M−1 s−1; L = 1,10-phenanthroline, 2.2 × 105 M−1 s−1. The rate constants for the reactions of the zwitterion form of glycine and α-alanine, CuNTA− + HL± = CuNTA(L)2− + H+, are 1.6 × 103 M−1 s−1 and 1.8 × 103 M−1 s−1, respectively. It was concluded that the reactions of the aliphatic ligands proceed through a dissociative interchange mechanism in which the axial coordination of the entering ligand is the rate-determining step. The unusually slow reactions with the aromatic ligands have been interpreted in terms of steric interference between the coordinated and entering ligands.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry