New directions in the preparation and redox chemistry of fluoride-templated tetranuclear vanadium phosphonate cage compounds, M(n+)[(V2O3)2(RPO3)4<F]n.
A new and simple preparation method for fluoride-templated tetranuclear vanadium phosphonate cage compounds, M(n+)[(V2O3)2(RPO3)4<F]n is outlined. The crystalline products were characterized by X-ray diffraction, elemental analysis, and thermogravimetric analysis. Using the acceptable solubility of the products, multinuclear NMR could be performed on the corresponding solutions. Some insight into the process of formation of the cage compounds in solution could be reached by monitoring the corresponding reaction mixture by multinuclear NMR. The template function of the F(-) ion could be demonstrated together with the fact that the non-transition-metal ions (M(n+)) used here (phosphonium ions) have no direct effect on the formation of the cage. In contrast, the redox behavior of these compounds in the solid state distinctly depends on the cations. This could be easily investigated by electron paramagnetic resonance because the mixed-valence species (3V(V)/V(IV)) can be produced chemically or thermally induced in solution as well as in the solid state. In the latter case, the reaction of the cage with H2 activated on the platinum powder can be regarded as a key experiment for understanding the redox process of the title compounds in the solid state. The role of specific interactions in solution at the tumbling rate and the localization of spin density in the cage could be demonstrated by the reduction performed with 1-methylimidazole and quinoline. While the substituents R = Me and Ph have only a small influence on the cage formation in solution, they have a significant influence on the redox reaction and structural relaxation in the solid state.
Jabor
Jabor K
JK
Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany. jabor.jabor@catalysis.de
Stösser
Reinhard
R
Feist
Michael
M
Neubauer
Petra
P
Meisel
Manfred
M