Transition Metal Chemistry

, Volume 31, Issue 3, pp 413–420 | Cite as

Kinetics and Mechanism of Chromium(III)-oxalates-2-hydroxynicotinate and Chromium(III)-oxalates-3-hydroxypicolinate Aquation in HClO4 Solutions

  • Małgorzata Pazderska-Szabłowicz
  • Agnieszka Białkowska
  • Ewa Kita
Article
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Abstract

New chromium(III) complexes, [Cr(C2O4)2(2-hnic)]2− and [Cr(C2O4)2(3-hpic)]2− (where 2-hnic = O,O′-bonded 2-hydroxynicotinic acid and 3-hpic = N,O-bonded 3-hydroxypicolinic acid), were obtained and characterized in solution. The acid-catalyzed aquation of the both complexes leads to liberation of the appropriate pyridinecarboxylic acid and formation of cis-[Cr(C2O4)2(H2O)2]−. Kinetics of these reactions were studied spectrophotometrically in the 0.1–1.0 M HClO4 range, at I = 1.0 M. In the case of [Cr(C2O4)2(2-hnic)]2−, a slow chelate-ring opening at the Cr–O (phenolate) bond is followed by a fast Cr–O (carboxylate) bond breaking. The rate law: kobs = kHQH[H+] was established, where kH is the acid-catalyzed rate constant and QH is the protonation constant of the coordinated phenolate oxygen atom. In the case of [Cr(C2O4)2(3-hpic)]2−, the reversible chelate-ring opening at Cr–N bond is followed by the rate determining step – the one-end bonded ligand liberation. The rate law for the first step was determined: kobs = k1+k−1/Q1[H+], where k1 and k−1 are the rate constants of the chelate-ring opening and closure and Q1 is the protonation constant of the pyridine nitrogen atom. The aquation mechanisms are proposed and the effect of ligand coordination mode on complex reactivity is discussed.

Keywords

Chromium HClO4 Rate Determine Step Coordination Mode Bond Breaking 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Copyright information

© Springer 2006

Authors and Affiliations

  • Małgorzata Pazderska-Szabłowicz
    • 1
  • Agnieszka Białkowska
    • 1
  • Ewa Kita
    • 1
  1. 1.Department of ChemistryN. Copernicus UniversityToruńPoland

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