Stereochemistry, paramagnetic species

The NMR has provided an invaluable tool in the elucidation of both the static and dynamic stereochemistry of metal complexes. Applications to both diamagnetic and paramagnetic species have been rewarding. In particular, the unique role of NMR as a mechanistic probe for the elucidation of fluxional processes in polynuclear metal carbonyl complexes should be noted. 

Analysis of vanadium-loaded model materials (such as EuY, amorphous aluminosilicate gels and EuY-gel mixtures) by electron paramagnetic resonance (EPR) has provided information concerning metal oxidation state and stereochemistry (67). EPR data has indicated that when vanadyl cations are introduced in the form of vanadyl naphthenate, they were stabilized in a zeolite with the faujasite structure as pseudo-octahedral V02+ even after calcination at 540°C. Upon steaming, these V02+ cations were then converted almost entirely to V+5 species (67). The formation of EuV04 was verified but the concentration of this vanadate was never proportional to the total rare-earth content of the zeolite. In EuY-gel mixtures the gel preferentially sorbed vanadium where it was stabilized mainly in the form of V205. 

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