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Homolytic Cleavage of Molecular Oxygen by Manganese Porphyrins Supported on Ag(111)

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Author

  • Barry E. Murphy
  • Sergey A. Krasnikov
  • Natalia N. Sergeeva
  • Attilio A. Cafolla
  • Alexei Preobrajenski
  • Alexander N. Chaika
  • Olaf Luebben
  • Igor V. Shvets

Summary, in English

Oxygen binding and cleavage are important for both molecular recognition and catalysis. Mn-based porphyrins in particular are used as catalysts for the epoxidation of alkenes, and in this study the homolytic cleavage of O-2 by a surface-supported monolayer of Mn porphyrins on Ag(111) is demonstrated by scanning tunneling microscopy, X-ray absorption, and X-ray photoemission. As deposited, {5,10,15,20-tetraphenylporphyrinato}Mn(III)CI(MnCITPP) adopts a saddle conformation with the average plane of its macrocyde parallel to the substrate and the axial CI ligand pointing upward, away from the substrate. The adsorption of MnCITPP on Ag(111) Is accompanied by a reduction of the Mn oxidation state from Mn(III) to Mn(II) due to charge transfer between the substrate and the molecule. Annealing the Mn(II)CITPP monolayer up to 510 K causes the chlorine ligands to desorb from the porphyrins while leaving the monolayer intact. The Mn(II)TPP is stabilized by the surface acting as an axial ligand for the metal center. Exposure of the Mn(11)TPP/Ag(111) system to molecular oxygen results in the dissociation of O-2 and forms pairs of Mn(111)OTPP molecules on the surface. Annealing at 445 K reduces the Mn(111)OTPP complex back to Mn(II)TPP/Ag(111). The activation energies for Cl and 0 removal were found to be 0.35 +/- 0.02 eV and 0.26 +/- 0.03 eV, respectively.

Department/s

Publishing year

2014

Language

English

Pages

5190-5198

Publication/Series

ACS Nano

Volume

8

Issue

5

Document type

Journal article

Publisher

The American Chemical Society (ACS)

Topic

  • Nano Technology

Keywords

  • porphyrins
  • axial ligand
  • self-assembly
  • scanning tunneling microscopy
  • X-ray absorption
  • X-ray photoemission

Status

Published

ISBN/ISSN/Other

  • ISSN: 1936-086X