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Rafal Jurczakowski, Grzegorz Litwinienko, Marek Orlik
Studies on the Formation and Kinetics of Self-Decomposition of Ni(IV)-N3− Complexes in Aqueous Media
Keywords: Nickel(IV)-Azide Complexes, Azide Oxidation, Kinetic Parameters, Spectroscopic Properties, Charge-Transfer Spectrum
Both electrochemical (at Pt electrode) and homogeneous (with Cl2(aq)) oxidation of the aqueous solution of Ni(II)-N3− yields the solution of a brown product that was found to be the azide complex of Ni(IV). Its UV/Vis spectrum, consisting of a single band of high intensity (ε = 26500 cm−1 dm3 mol−1 at λmax = 471 nm), has been ascribed to the ligand-to-metal charge-transfer mechanism (LMCT). The Ni(IV)-N3− complex undergoes spontaneous decomposition in aqueous solution, with Ni(IV) reduced back to Ni(II) and N3− oxidized to molecular nitrogen. The first-order kinetics of this process was studied spectrophotometrically and the following parameters were found: rate constant k = 1.96×10−2 s−1, Arrhenius activation energy Ea = 82±7 kJ mol−1, standard activation enthalpy ΔH≠0 = 79±7 kJ mol−1, and small standard activation entropy ΔS≠0 = 10±20 J mol−1 K−1. The outline mechanism for the intramolecular redox Ni(IV)-N3− decomposition has been suggested. Nickel ions at various oxidation states were found to be powerful catalysts for the redox processes of azide ions.
Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0942-9352
Volume: 220, 08/2006
Pages: 1083 - 1099