Kinetics and mechanism of a macrocyclic chromium(III) complex oxidation to chromium(IV) by hexacyanoferrate(III) in strongly alkaline media

J. Chatlas, O. Impert, A. Katafias, P. Kita, G. Wrzeszcz, J. Eriksen, O. Monsted, A. Mills

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Oxidation of the macrocyclic Cr(III) complex cis-[Cr(cycb)(OH)(2)](+), where cycb = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, by an excess of the hexacyanoferrate( III) in basic solution, slowly produces Cr(V) species. These species, detected using e.p.r. spectroscopy, are stable under ambient conditions for many hours, and the hyperfine structure of the e.p.r. spectrum is consistent with the interaction of the d-electron with four equivalent nitrogen nuclei. Electro-spray ionization mass spectrometry suggests a concomitant oxidation of the macrocyclic ligand, in which double bonds and double bonded oxygen atoms have been introduced. By comparison basic chromate(III) solutions are oxidized rapidly to chromate(VI) by hexacyanoferrate(III) without any detectable generation of stable Cr(V) intermediates. Kinetics of oxidation of the macrocyclic Cr(III) complex in alkaline solution has been studied under excess of the reductant. Rate determining formation of Cr(IV) by a second order process involving the Cr(III) and the Fe(III) reactants is seen. This reaction also involves a characteristic higher order than linear dependence on the hydroxide concentration. Reaction mechanisms for the processes, including oxidation of the coordinated macrocyclic ligand under excess of the oxidant- are proposed.
Original languageEnglish
Pages (from-to)634-643
Number of pages9
JournalTransition Metal Chemistry
Volume29
Issue number6
DOIs
Publication statusPublished - Sep 2004

Keywords

  • HYDROGEN-PEROXIDE
  • LIGANDS
  • ION
  • DISPROPORTIONATION
  • CHEMISTRY
  • REDUCTION
  • CORROLES
  • ESR
  • EPR

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