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Title: Reaction of coordinated ligands: Complex formation between nickel (II) and pyridine- 2-carboxylato-/pyridine- 3-carboxylato-pentaamminecobalt (III) ions and aquation of the cobalt (III) substrates catalysed by nickel (II) and copper (II) - A kinetic and mechanistic study
Authors: Das, Nigamananda
Dash, Anadi C
Issue Date: Jun-1993
Publisher: NISCAIR-CSIR, India
Abstract: The carboxylatopentaarnminecobalt (III) ions derived from pyridine-2-, and pyridine-3-carboxylates bind, Ni(II) and Cu(II) to form binuclear species. The kinetics of reversible formation of the binuclear species (NH3)5CoO2C - (2/)pyNi4+ (Py = C5H4N) was investigated by stopped-flow technique at 10-35°C, [Ni2+]T: 11 = 0.005-0.05; and 1= 0.3 mol dm3. The kobs values fitted 10 the relationship kobs = kfKeq[NiF+]/(1 + Keq [Ni2+] consistent with the reaction Scheme N5CoO2CC5H4N2+ + Ni(OH2) N5CoO2CC5H4N-Ni(OH2)   N5CoO2CC5H4NNi(OH2). This is in contrast to the reversible complexation of Ni(II) with the pyridine-3-analogue under comparable condition for which chelation step is not involved. The resulting binuclear complexes of pyridine-2-carboxylato complex promoted aquation at the cobalt (III) centre (NH3)5CoO2C-(2-)pyM(n+2)+(NH3)5CoOH + py(- 2 - )CO2Mn+ the effect of the metal ions being in the order Cu2+ > Ni2+. The rate data for dissociation of binuclear species as well as catalytic activities of the metal ions in promoting water for carboxylate substitution at the cobalt (III) centre are consistent with the fact that the metal ions are chelated by pyridine-nitrogen and cobalt (III) bound carboxylate group of pyridine-2-carboxylate.
Page(s): 531-535
ISSN: IJC-A Vol.32A(06) [June 1993]
Appears in Collections:IJC-A Vol.32A(06) [June 1993]

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