Journal of Cluster Science

, Volume 17, Issue 2, pp 143–165 | Cite as

Polyoxoanion with Octahedral Germanium(IV) Hetero Atom: Synthesis, Structure, Magnetism, EPR, Electrochemistry and XPS Studies on the Mixed-Valence 14-Vanadogermanate [GeVV12VIV2O40]8−

  • Li-Hua Bi
  • Ulrich Kortz
  • Michael H. Dickman
  • Saritha Nellutla
  • Naresh S. Dalal
  • Bineta Keita
  • Louis Nadjo
  • Manuel Prinz
  • Manfred Neumann
Article

Abstract

The mixed-valence 14-vanadogermanate [GeVV12VIV2O40]8− (1) has been synthesized and characterized in solution by 51V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K2Na6[GeVV12VIV2O40]·10H2O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) Å, b=11.6205(3) Å, c=20.2658(5) Å, and Z=2. Polyanion 1 is composed of a central GeIVO6 octahedron which is surrounded by a total of 14 VO6 octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two VIV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two VIV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two VIV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a VIV ion, suggesting a possible ground state of \(3d_{x^{2}-y^{2}}.\) XPS measurements on KNa-1 also confirmed the coexistence of VV and VIV in 1.

Keywords

Polyoxovanadate mixed-valence cluster self-assembly germanium X-ray crystallography 51V NMR magnetism EPR electrochemistry XPS 

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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Li-Hua Bi
    • 1
  • Ulrich Kortz
    • 1
  • Michael H. Dickman
    • 1
  • Saritha Nellutla
    • 2
  • Naresh S. Dalal
    • 2
  • Bineta Keita
    • 3
  • Louis Nadjo
    • 3
  • Manuel Prinz
    • 4
  • Manfred Neumann
    • 4
  1. 1.School of Engineering and ScienceInternational University BremenBremenGermany
  2. 2.Department of Chemistry and Biochemistry, National High Magnetic Field Laboratory, Center for Interdisciplinary Magnetic ResonanceFlorida State UniversityTallahasseeUSA
  3. 3.Laboratoire de Chimie Physique, UMR 8000, CNRS, Equipe d’Electrochimie et PhotoélectrochimieUniversité Paris-SudOrsay CedexFrance
  4. 4.Department of PhysicsUniversity of OsnabrückOsnabrückGermany

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