Thermodynamic and kinetic studies on the complexation reactions of copper(II) with NN′-bis(β-carbamoylethyl)-trans-cyclohexane-1,2-diamine

Abstract

The interactions of NN′-bis(β-carbamoylethyl)-trans-cyclohexane-1,2-diamine (L) and copper(II) in aqueous solution have been investigated by potentiometric and spectrophotometric techniques. The log K values for the protonation constants of the ligand at 25.0 °C and 0.1 mol dm^–3 NaClO₄ are 9.34 and 4.49. The log K value for the formation constant of [Cu(L)]²⁺ is 12.92, and the log K values for the deprotonation constants of [Cu(L)]²⁺ and [Cu(H_–1L)]⁺ are –7.72 and –9.02 respectively. Electronic spectra of [Cu(L)]²⁺, [Cu(H_–1L)]⁺, and [Cu(H_–2L)] have been recorded and are discussed. The complexation kinetics of copper(II) with this ligand have been studied under the conditions using the stopped-flow technique. The resolved formation rate constants (in 0.10 mol dm^–3 NaClO₄ at 25.0 °C) for copper(II) reacting with the unprotonated and monoprotonated ligand, L. and HL⁺, are 4.83 × 10⁷ and 4.10 × 10² dm³ mol^–1 s^–1 respectively. Two possible pathways for the complexation reaction are discussed.