In Situ Mossbauer Spectroscopy of a Species Irreversibly Adsorbed on an Electrode Surface

Cristian A. Fierro, Madan Mohan, Daniel Alberto Scherson

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The redox properties of μ-oxobis[iron meso-tetrakis(methoxyphenyl)porphyrin] (FeTMPP)20, adsorbed on high-area carbon in alkaline solutions have been examined in situ by using Mossbauer spectroscopy at cryogenic temperatures. The spectrum obtained for the electrode polarized at 0.0 V vs Hg/HgO,OH-yielded at 100 K a doublet with parameters resembling those of bulk crystalline (FeTMPP)20. Similar measurements with the electrode polarized at -0.9 V at the same temperature displayed in addition to the original feature two new doublets with Mossbauer parameters consistent with the presence of a high-spin ferrous (S = 2) and either a high-spin ferric (5 = 5/2) or an intermediate-spin ferrous porphyrin species (S = 1). As the temperature was increased, these new features collapsed into a single doublet with an isomer shift intermediate between those observed at 100 K. Two possible models have been suggested to account for these results: (i) the formation of a mixed-valence μ-oxo-type porphyrin, which below the spin trapping temperature would give rise to ferrous and ferric sites, and (ii) the full reduction and dissociation of the dimer following the first electron transfer, to yield an intermediate-spin and a high-spin ferrous porphyrin. The possibility of impurities being responsible for some of the spectroscopic features has also been considered.

Original languageEnglish
Pages (from-to)1338-1342
Number of pages5
JournalLangmuir
Volume6
Issue number8
DOIs
Publication statusPublished - 1990 Jan 1
Externally publishedYes

Fingerprint

Porphyrins
Mossbauer spectroscopy
porphyrins
Electrodes
electrodes
spectroscopy
Temperature
Isomers
Dimers
Cryogenics
Carbon
Iron
Impurities
cryogenic temperature
Crystalline materials
temperature
Electrons
electron transfer
isomers
trapping

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

Cite this

In Situ Mossbauer Spectroscopy of a Species Irreversibly Adsorbed on an Electrode Surface. / Fierro, Cristian A.; Mohan, Madan; Scherson, Daniel Alberto.

In: Langmuir, Vol. 6, No. 8, 01.01.1990, p. 1338-1342.

Research output: Contribution to journalArticle

Fierro, Cristian A. ; Mohan, Madan ; Scherson, Daniel Alberto. / In Situ Mossbauer Spectroscopy of a Species Irreversibly Adsorbed on an Electrode Surface. In: Langmuir. 1990 ; Vol. 6, No. 8. pp. 1338-1342.
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abstract = "The redox properties of μ-oxobis[iron meso-tetrakis(methoxyphenyl)porphyrin] (FeTMPP)20, adsorbed on high-area carbon in alkaline solutions have been examined in situ by using Mossbauer spectroscopy at cryogenic temperatures. The spectrum obtained for the electrode polarized at 0.0 V vs Hg/HgO,OH-yielded at 100 K a doublet with parameters resembling those of bulk crystalline (FeTMPP)20. Similar measurements with the electrode polarized at -0.9 V at the same temperature displayed in addition to the original feature two new doublets with Mossbauer parameters consistent with the presence of a high-spin ferrous (S = 2) and either a high-spin ferric (5 = 5/2) or an intermediate-spin ferrous porphyrin species (S = 1). As the temperature was increased, these new features collapsed into a single doublet with an isomer shift intermediate between those observed at 100 K. Two possible models have been suggested to account for these results: (i) the formation of a mixed-valence μ-oxo-type porphyrin, which below the spin trapping temperature would give rise to ferrous and ferric sites, and (ii) the full reduction and dissociation of the dimer following the first electron transfer, to yield an intermediate-spin and a high-spin ferrous porphyrin. The possibility of impurities being responsible for some of the spectroscopic features has also been considered.",
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AB - The redox properties of μ-oxobis[iron meso-tetrakis(methoxyphenyl)porphyrin] (FeTMPP)20, adsorbed on high-area carbon in alkaline solutions have been examined in situ by using Mossbauer spectroscopy at cryogenic temperatures. The spectrum obtained for the electrode polarized at 0.0 V vs Hg/HgO,OH-yielded at 100 K a doublet with parameters resembling those of bulk crystalline (FeTMPP)20. Similar measurements with the electrode polarized at -0.9 V at the same temperature displayed in addition to the original feature two new doublets with Mossbauer parameters consistent with the presence of a high-spin ferrous (S = 2) and either a high-spin ferric (5 = 5/2) or an intermediate-spin ferrous porphyrin species (S = 1). As the temperature was increased, these new features collapsed into a single doublet with an isomer shift intermediate between those observed at 100 K. Two possible models have been suggested to account for these results: (i) the formation of a mixed-valence μ-oxo-type porphyrin, which below the spin trapping temperature would give rise to ferrous and ferric sites, and (ii) the full reduction and dissociation of the dimer following the first electron transfer, to yield an intermediate-spin and a high-spin ferrous porphyrin. The possibility of impurities being responsible for some of the spectroscopic features has also been considered.

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