The electronic structure of reduced phosphovanadomolybdates and the implications on their use in catalytic oxidation initiated by electron transfer

Hajime Hirao, Devesh Kumar, Hui Chen, Ronny Neumann, Sason Shaik

Research output: Contribution to journalArticle

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Abstract

The geometries and electronic structures of the five isomers of [PV 2Mo10O40]5- and its mono- and direduced species were theoretically investigated by means of B3LYP calculations, with an attempt to understand their role as oxidative catalysts in electron-transfer-initiated processes. The calculations reveal the following features: (a) Either in the gas phase or in a solvent, the reduction of the [PV2Mo10O40]5- produces [PV 2Mo10O40]6,7- ions in which the excess electrons are localized on the vanadium atoms in the corresponding δ orbitals. By contrast, the direduced [PV2Mo 10O40]7- isomers where the one electron is localized on molybdenum are high in energy. Consequently, whereas the five isomers of [PV2Mo10O40]5- have roughly a statistical distribution, in the direduced species, the 1,4-[PV 2Mo10O40]7- isomer becomes more stable than others. (b) The gas-phase reduction of the parent [PMo 12O40]3- anion is exceedingly more favorable (by ca. 250 kcal/mol) than the reduction of [PV2Mo10O 40]5-. By contrast, contribution of the solvent exerts a strong leveling effect and makes the reduction potentials of the two species very similar, (c) Since the reduction of [PV2Mo10O 40O40]5- concentrates high negative charge near the O=VO4 moiety, this negative charge accumulation will act as an attractor that binds the organic radical cation (cation), which causes a subsequent proton transfer to an oxo ligand of the vanadium. As such, in terms of an electron-transfer catalytic effect, the presence of vanadium in [PV 2Mo10O40]5- creates function for the catalyst, (d) The computations reveal that [PV2Mo10O 40]7- is a diradicaloid that possesses two virtually degenerate states, with singlet and triplet spins. Thus, we may expect two-state reactivity (TSR) in the catalytic reactions of [PV2Mo 10O40]5-. Some predictions are made based on these features.

Original languageEnglish
Pages (from-to)7711-7719
Number of pages9
JournalJournal of Physical Chemistry C
Volume111
Issue number21
DOIs
Publication statusPublished - May 31 2007

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Catalytic oxidation
Electronic structure
electron transfer
isomers
Isomers
Vanadium
vanadium
electronic structure
oxidation
Electrons
Cations
vapor phases
catalysts
cations
Gases
Positive ions
leveling
statistical distributions
Catalysts
Proton transfer

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

The electronic structure of reduced phosphovanadomolybdates and the implications on their use in catalytic oxidation initiated by electron transfer. / Hirao, Hajime; Kumar, Devesh; Chen, Hui; Neumann, Ronny; Shaik, Sason.

In: Journal of Physical Chemistry C, Vol. 111, No. 21, 31.05.2007, p. 7711-7719.

Research output: Contribution to journalArticle

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abstract = "The geometries and electronic structures of the five isomers of [PV 2Mo10O40]5- and its mono- and direduced species were theoretically investigated by means of B3LYP calculations, with an attempt to understand their role as oxidative catalysts in electron-transfer-initiated processes. The calculations reveal the following features: (a) Either in the gas phase or in a solvent, the reduction of the [PV2Mo10O40]5- produces [PV 2Mo10O40]6,7- ions in which the excess electrons are localized on the vanadium atoms in the corresponding δ orbitals. By contrast, the direduced [PV2Mo 10O40]7- isomers where the one electron is localized on molybdenum are high in energy. Consequently, whereas the five isomers of [PV2Mo10O40]5- have roughly a statistical distribution, in the direduced species, the 1,4-[PV 2Mo10O40]7- isomer becomes more stable than others. (b) The gas-phase reduction of the parent [PMo 12O40]3- anion is exceedingly more favorable (by ca. 250 kcal/mol) than the reduction of [PV2Mo10O 40]5-. By contrast, contribution of the solvent exerts a strong leveling effect and makes the reduction potentials of the two species very similar, (c) Since the reduction of [PV2Mo10O 40O40]5- concentrates high negative charge near the O=VO4 moiety, this negative charge accumulation will act as an attractor that binds the organic radical cation (cation), which causes a subsequent proton transfer to an oxo ligand of the vanadium. As such, in terms of an electron-transfer catalytic effect, the presence of vanadium in [PV 2Mo10O40]5- creates function for the catalyst, (d) The computations reveal that [PV2Mo10O 40]7- is a diradicaloid that possesses two virtually degenerate states, with singlet and triplet spins. Thus, we may expect two-state reactivity (TSR) in the catalytic reactions of [PV2Mo 10O40]5-. Some predictions are made based on these features.",
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