Chapter 4 - Jacobs University

Chapter 7
Pt-containing Polyoxometalate
temperature and/or downfield shift of the NMR signals with increasing temperature (by about 3
ppm). In addition, the fact that two molecules of 5 form hydrogen-bonded dimers in the solid
state (Figure 7.5) could also be important. It is possible that the NMR spectrum at 293 K actually
corresponds to the weakly bound dimer assembly, whereas heating to 333 K breaks them apart,
resulting in monomeric 5. . It must be remembered that the 51 VNMR experiments take several
hours. We plan to investigate the thermodynamic stability of the dimer assembly in the future by
using appropriate techniques (e.g. size exclusion chromatography, ultracentrifugation, cryo-mass
spectrometry).
Figure 7.5 Dimer formation of 5 in the solid state via hydrogen bonding.
Already more than 30 years ago Pope and O’Donnell investigated the decavanadate ion
V 10 by 51 VNMR spectroscopy in solution, and they discovered that the chemical shifts are pH
dependent. 17 Since then also other groups have engaged in 51 Vand 17 7a, 18
O NMR studies of V 10 but to our knowledge no study on the temperature dependence of the chemical shifts has been
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