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The mixed valence compound Na2Fe2F7 crystallizes in the monoclinic weberite structure of the Na2CuFeF7‐II type (M‐II), space group C2/c, Z = 16, a = 12.676, b = 7.422, c = 24.710 Å, β = 99.97°. Refinement on F2 led to wR(F2) = 0.117 for all 2 645 reflections, R = 0.057 for 1 258 refl. with Fo > 4σ(F). On the basis of this and other recent single crystal investigations the structures of weberites Na2MIIMIIIF7 are classified in four main structure types: O‐I is the ‘classical’ orthorhombic weberite type (S.G. Imma) encountered e.g. in the mineral Na2MgAlF7, from which two lower symmetric variants O‐II (Na2CuCrF7 type) and O‐III (Na2NiInF7) are deriving. The second M‐I and third M‐II basic type are monoclinic (e. g. Na2CuFeF7‐I and ‐II), the fourth type T is trigonal (Na2MnFeF7). The structural relations within the weberite family are discussed and the connections established, which allow to regard these weberites as well as the pyrochlores as subtraction derivatives of the fluorite type.

In the crystal structure of hydrothermally synthesized disodium manganese fluoride orthophosphate, Na2{MnF[PO4]}, two kinds of cis-MnO4F2 octahedra share common vertices to form (Mn2F2Os) chains parallel to the b axis of the monoclinic unit cell. In the a and c directions these chains are linked by PO4 tetrahedra to form a three-dimensional framework of octahedra and tetrahedra. Na + cations are located in the channels of this framework structure. The problem of {OTXs} mixed anionic radical polymorphism is discussed. CommentThis work is part of our efforts to synthesize and investigate pegmatite-related phosphates. We are interested in the relationship between the structures of transition metal phosphates and the conditions of their formation (Yakubovich & Urusov, 1996). In addition to this, first row transition metal phosphates have become a focus for interest in recent years because of their possible use as new non-linear optical materials such as KTiOPO4 (KTP). The crystals of the new compound, Na2{MnF[PO4]}, were obtained as the product of hydrothermal growth experiments in the system NaF-MnO-(NH4)2HPO4-H20.

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