Structural, spectroscopic and magnetic studies of VIIMIVF6 compounds with MIV = Zr, Nb

In the context of a study on the magnetic properties of fluoroniobates IV the new compound VNbF6 has been prepared then characterized by X-ray diffraction and diffuse reflectance spectroscopy. The 3D framework of rhomboedral VNbF6, related to that of LiSbF6, is built up from corner sharing NbF6 and VF6 octahedra; it allows superexchange interactions between Nb4+ and V2+. The ferrimagnetic behaviour of VNbF6 (Tc ∼ 38 K) is discussed in relation to the magnetic properties of isotypic compounds M'NbF6 (M' = Mn, Fe). The new paramagnetic compound VZrF6 has been also synthesized and characterized.