(H2O)"VIII2F6" and Pyr-VF3:Hydrothermal Synthesis, Structure Determination, and Magnetic Characterization of New Fluorides with the Pyrochlore Type

Small green triangular crystals of a new tridimensional hydrated vanadium(III) fluoride have been hydrothermally prepared in a simple way by heating a mixture of V:HF:H2O in the molar ratio 1:1:50 at 200°C for 3 days. Its structure was solved by X-ray diffraction in the cubic space group Fd3m (No. 227) with a=10.4636(2) ?. (H2O)"VIII2F6" presents the structure of the wellknown pyrochlore type. The cavities contain water molecules which are lost by heating (T<250°C) without any structural change. The thermal stability of this new form of VF3 (Pyr-VF3) with the pyrochlore structure is compared to that of the already known Pyr-FeF3. The magnetic behavior of Pyr-VF3 is described.