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  • Author or Editor: D. Bardhan x
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Abstract  

Reactions of carbonate radical (Co3 ) generated by photolysis or by radiolysis of a carbonate solution, with Cu(II) complexes of aminopolycarboxylic acids viz., Cu(II)ethylenediamine tetraacetate [CuIIEDTA]2− and Cu(II)-iminodiacetate [CuIIIDA] were studied at pH 10. 5 and ionic strength 0.2 mol·dm−3. Time-resolved spectroscopy and kinetics for the transients were studied using flash photolysis and stable products arising from the ligand degradation of the complex were ascertained by steady-state radiolysis experiments. From the kinetic data it is observed that CO3 , radical reacts initially with CuII-complex to form a transient intermediate having maximum absorption at 335 nm and 430 nm. From the subsequent reactions of this intermediate it was assigned to be CuIII. species. This Cu(III) species undergoes intermolecular electron transfer with the CuII-complex to give a radical intermediate which again slowly reacts with CuII-complex to give a long lived species containing Cu−C bond. This long lived species, however, slowly decomposed to give glyoxalic reaction between CuIII-complex and a suitable donor, the one electron reduction potential for [CuIIIEDTA]1−/[CuIIEDTA]2− and [CuIIIIDA]+1/CuIIIDA was determined.

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Abstract  

Reactions of carbonate radical (CO3 ), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm–3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·106 dm3·mol–1·s–1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·102·s–1) to give a radical intermediate of the type Ni(II)RNHCHCO 2 ) which rapidly forms an adduct containing a Ni–C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.

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Abstract  

Reactions of carbonate (CO 3 –· ) and bicarbonate (HCO 3 · ) radicals generated by photolysis of a carbonate or bicarbonate solution at pH 11.2 and 8.5, respectively, with Co(II) complexes of iminodiacetic acid (IDA) and ethylenediaminetetraacetic acid (EDTA) have been studied. The rate constants for the reactions were in the order of 106–107 dm3mol–1s–1. From the time-resolved spectroscopy of the products formed after reaction of CO –· or HCO 3 · , it is observed that CO 3 –· or HCO 3 · oxidize the metal center to its higher oxidation state.

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