Use of ESR for the structural study of crystals of heteropoly compounds
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The results obtained from the ESR spectra of the 12-molybdophosphates, like the x-ray diffraction data, provide evidence in support of the existence of a cubic three-dimensional network formed by Keggin anions. Because of their large dimensions (∼14 Å in the outer sphere), this framework, in spite of the spherical symmetry of the anions and even with close packing contains large cavities in which different cations may be situated. There probably exists a large number of “pockets” for the stabilization of cations, as indicated by the fact that the spectra of paramagnetic atoms characteristic of single crystals are not observed. Moreover, the dimensions of the cavities probably permit the movement of whole molecules. In this connection, we might ask the question (this of course does not follow from the experimental results of the present work): It is possible that some HPC, with compositions corresponding to highly substituted salts of heteropolyacids, represent a variety of inclusion compound? The information may be provided by further studies.
KeywordsPhysical Chemistry Inorganic Chemistry Diffraction Data Structural Study Large Dimension
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