Kinetics and mechanism of the metal exchange reaction between N,N’-bis(β-carbamoylethyl) ethylendiamine nickel(II) and copper(II)

The kinetics of the [Ni N,N’-bis(β-carbamoylethyl) ethylendiamine)]2+/Cu2+, Ni(bcen)2+/Cu2+ metal exchange reaction in aqueous solution has been studied using spectrophotometry to follow Cu(bcen)2+ formation at 640 nm (bcen is N,N’- bis(β-carbamoylethyl) ethylendiamine). The reaction was studied at pH 6.9, ionic strength 0.5 M and in the temperature range 15 to 35 °C. The kinetics was studied under pseudo-order conditions with [Ni(bcen)2+] >> [Cu2+]. The reaction this under the condition has been found to be a two-step process mechanism is proposed involving: (1) partially dissociation of the Ni(bcen)2+ complex, following with formation of a dinuclear intermediate and (2) metal exchange. Step 1 is rapid and depends on [Ni(bcen)2+] while step 2 is rate determining and independent of [Ni(bcen)2+]. The rate constants k1 (step 1) and k2 (step 2) are 4.40 + 0.14 M–1s–1 and (11.25 + 0.94) × 10–2 s–1 respectively at 25 °C. Activation parameters are also reported.