Kinetics and mechanism of complex-formation reactions of ammonia and methylamine with copper(II) complexes in aqueous solution

Abstract

The complex-formation kinetics of copper(II) complexes with ammonia and methylamine was investigated by the temperature-jump relaxation technique. At 2 mol dm^–3 ionic strength the forward rate constants (dm³ mol^–1 s^–1) for the studied reactions are: [Cu(NH₃)]²⁺+ NH₃⇌[Cu(NH₃)₂]²⁺, (1.2 ± 0.1)× 10⁸(7 °C); [Cu(ida)]+ NH₃⇌[Cu(ida)(NH₃)], (3.7 ± 0.3)× 10⁸; [Cu(ida)]+ NMeH₂⇌[Cu(ida)(NMeH₂)], (8.7 ± 0.3)× 10⁷; [Cu(mida)]+ NMeH₂⇌[Cu(mida)(NMeH₂)]. (5.4 ± 0.3)× 10⁷(25 °C); ida = iminodiacetate, mida =N-methyliminodiacetate. The results presented and those from previous literature strongly suggest that specific interactions between the co-ordinated groups and the central metal ion do not modify the kinetics and mechanism of the complex formation. The kinetic data are consistent with the Eigen–Wilkins mechanism.