Temperature- and pressure-dependent kinetico-mechanistic studies on the formation of mixed-valence {(tetraamine)CoIIINCFeII(CN) 5}- units

Laura Alcázar, Virág Bogdándi, G. Lente, Manuel Martínez, Marta Vázquez

Research output: Article

2 Citations (Scopus)

Abstract

The reduction of CoIII in the tetraamine-encapsulating ligand complex [CoIII{(-ET)(Me2)cyclen}(H2O)2]3+ by [FeII(CN)6]4- has been studied kinetico-mechanistically at different pH, temperatures, and pressures. The process agrees with the expected outer-sphere redox mechanism, with the value of the encounter-complex equilibrium constant large enough to allow for kinetic determination of the first-order electron transfer reaction rate constant. The value of the encounter-complex equilibrium constant, Kpre-eq, is not only dependent on the charge of the redox partners, but also on the establishment of an important network of hydrogen bonds. These can also explain the differences obtained in the activation volumes determined for the diaqua and bis-hydroxo complexes. Neither the leaching of CoII nor the presence of [FeIII(CN)6]3- is observed in the final reaction medium, which indicates that a fast sequence involving substitution on the transient CoII complex followed by a fast inner-sphere electron transfer takes place. This sort of mechanism has already been established for encapsulating pentaamine ligand complexes, but this is the first example of such a sequential reaction occurring on a tetradentate ligand complex. Preliminary UV-Vis and electrochemical characterization experiments have been conducted on the final reaction mixtures, suggesting the formation of a stable cyanide-bridged CoIII/FeII mixed-valence complex of the same type reported in the literature for encapsulating {CoIII(N)5} skeletons.

Original languageEnglish
Pages (from-to)3058-3068
Number of pages11
JournalJournal of Coordination Chemistry
Volume68
Issue number17-18
DOIs
Publication statusPublished - aug. 4 2015

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encapsulating
Ligands
Equilibrium constants
valence
encounters
ligands
electron transfer
Electrons
Cyanides
cyanides
leaching
musculoskeletal system
Temperature
Leaching
Reaction rates
temperature
Rate constants
Hydrogen bonds
reaction kinetics
Substitution reactions

ASJC Scopus subject areas

  • Materials Chemistry
  • Physical and Theoretical Chemistry

Cite this

Temperature- and pressure-dependent kinetico-mechanistic studies on the formation of mixed-valence {(tetraamine)CoIIINCFeII(CN) 5}- units. / Alcázar, Laura; Bogdándi, Virág; Lente, G.; Martínez, Manuel; Vázquez, Marta.

In: Journal of Coordination Chemistry, Vol. 68, No. 17-18, 04.08.2015, p. 3058-3068.

Research output: Article

Alcázar, Laura ; Bogdándi, Virág ; Lente, G. ; Martínez, Manuel ; Vázquez, Marta. / Temperature- and pressure-dependent kinetico-mechanistic studies on the formation of mixed-valence {(tetraamine)CoIIINCFeII(CN) 5}- units. In: Journal of Coordination Chemistry. 2015 ; Vol. 68, No. 17-18. pp. 3058-3068.
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abstract = "The reduction of CoIII in the tetraamine-encapsulating ligand complex [CoIII{(-ET)(Me2)cyclen}(H2O)2]3+ by [FeII(CN)6]4- has been studied kinetico-mechanistically at different pH, temperatures, and pressures. The process agrees with the expected outer-sphere redox mechanism, with the value of the encounter-complex equilibrium constant large enough to allow for kinetic determination of the first-order electron transfer reaction rate constant. The value of the encounter-complex equilibrium constant, Kpre-eq, is not only dependent on the charge of the redox partners, but also on the establishment of an important network of hydrogen bonds. These can also explain the differences obtained in the activation volumes determined for the diaqua and bis-hydroxo complexes. Neither the leaching of CoII nor the presence of [FeIII(CN)6]3- is observed in the final reaction medium, which indicates that a fast sequence involving substitution on the transient CoII complex followed by a fast inner-sphere electron transfer takes place. This sort of mechanism has already been established for encapsulating pentaamine ligand complexes, but this is the first example of such a sequential reaction occurring on a tetradentate ligand complex. Preliminary UV-Vis and electrochemical characterization experiments have been conducted on the final reaction mixtures, suggesting the formation of a stable cyanide-bridged CoIII/FeII mixed-valence complex of the same type reported in the literature for encapsulating {CoIII(N)5} skeletons.",
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N2 - The reduction of CoIII in the tetraamine-encapsulating ligand complex [CoIII{(-ET)(Me2)cyclen}(H2O)2]3+ by [FeII(CN)6]4- has been studied kinetico-mechanistically at different pH, temperatures, and pressures. The process agrees with the expected outer-sphere redox mechanism, with the value of the encounter-complex equilibrium constant large enough to allow for kinetic determination of the first-order electron transfer reaction rate constant. The value of the encounter-complex equilibrium constant, Kpre-eq, is not only dependent on the charge of the redox partners, but also on the establishment of an important network of hydrogen bonds. These can also explain the differences obtained in the activation volumes determined for the diaqua and bis-hydroxo complexes. Neither the leaching of CoII nor the presence of [FeIII(CN)6]3- is observed in the final reaction medium, which indicates that a fast sequence involving substitution on the transient CoII complex followed by a fast inner-sphere electron transfer takes place. This sort of mechanism has already been established for encapsulating pentaamine ligand complexes, but this is the first example of such a sequential reaction occurring on a tetradentate ligand complex. Preliminary UV-Vis and electrochemical characterization experiments have been conducted on the final reaction mixtures, suggesting the formation of a stable cyanide-bridged CoIII/FeII mixed-valence complex of the same type reported in the literature for encapsulating {CoIII(N)5} skeletons.

AB - The reduction of CoIII in the tetraamine-encapsulating ligand complex [CoIII{(-ET)(Me2)cyclen}(H2O)2]3+ by [FeII(CN)6]4- has been studied kinetico-mechanistically at different pH, temperatures, and pressures. The process agrees with the expected outer-sphere redox mechanism, with the value of the encounter-complex equilibrium constant large enough to allow for kinetic determination of the first-order electron transfer reaction rate constant. The value of the encounter-complex equilibrium constant, Kpre-eq, is not only dependent on the charge of the redox partners, but also on the establishment of an important network of hydrogen bonds. These can also explain the differences obtained in the activation volumes determined for the diaqua and bis-hydroxo complexes. Neither the leaching of CoII nor the presence of [FeIII(CN)6]3- is observed in the final reaction medium, which indicates that a fast sequence involving substitution on the transient CoII complex followed by a fast inner-sphere electron transfer takes place. This sort of mechanism has already been established for encapsulating pentaamine ligand complexes, but this is the first example of such a sequential reaction occurring on a tetradentate ligand complex. Preliminary UV-Vis and electrochemical characterization experiments have been conducted on the final reaction mixtures, suggesting the formation of a stable cyanide-bridged CoIII/FeII mixed-valence complex of the same type reported in the literature for encapsulating {CoIII(N)5} skeletons.

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