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The magnetic properties of two polyoxovanadate anions, (V12As8O40(HCO2))3- and (V12As8O40(HCO2))5- were investigated. The results suggest that in the former compound there are six vanadium(IV) and six vanadium(V) ions, while in the latter there are eight vanadium(IV) and four vanadium(V) ions. The electron paramagnetic resonance spectra of the two compounds show opposite behaviors at low and high fields, probably due to field-dependent relaxation effects.

The magnetic properties of K6(H3KV12As3O39 AsO4).8H2O were investigated to test the ability of valence bond summations to identify the localized and delocalized vanadium(IV) centers in polyoxovanadates. A model which accounts for the antiferromagnetic coupling constant J between the three localized vanadium(IV) ions and an effective coupling constant J' between the localized and delocalized vanadium(IV) centers was used. Parameters obtained from fitting the experimental thermal variation of (sub khi)T revealed that coupling constants depend greatly on the geometry of the complexes.