Single crystals of six compounds (Ba2CaMM2F14)-M-II-F-III were prepared to refine their usovite type structure (space group C2/c, Z = 4) using X-ray diffractometer data. The cell parameters of the phases studied with (MM2III)-M-II = MnV2, FeV2, CuMn2, MnFe2, CuFe2 und CuGa2 are within the range 1374 less than or equal to a/pm less than or equal to 1384, 534 less than or equal to b/pm less than or equal to 5542, 1474 less than or equal to c/pm less than or equal to 1510, 91.3 less than or equal to beta/degrees less than or equal to 93,2. The atoms Ca and M-II are incompletely ordered on the 8- and 6-coordinated positions, 4e and 4b, respectively. In the case of Ba2CaFeV2F]4 and Ba2CaCuGa2F14 there is reciprocal substitution (x 0,1): (Ca1-xMxII) (4e) and ((M1-xCax)-Ca-II) (4b). In the case of the other usovites Ca-enriched phases Ba2Ca((M1-yCay)-Ca-II)(M2F14)-F-III occured (up to y approximate to 0.35), exhibiting partial substitution at the octahedral position (4b) only, showing a corresponding increase in M-II-F distances. The distortion of [(MF6)-F-II] and [(MF6)-F-III] octahedra within the structure is considerably enhanced on replacement by Cull and Muni. The results of powder magnetic susceptibility measurements of Ba2CaMnV2F14 and Ba2CaFeV2F14 (T-N approximate to 7K) are reported.

The structural and magnetic properties of Na2CoMF7 compounds (M = Al, Cr, Fe), showing a new structure deriving from that of weberite have been investigated. The monoclinic structure, favored by cobalt (II) ions, is intermediate between the orthorhombic type (Na2NiFeF7) and the trigonal type (Na2MnFeF7). It exhibits (CoF5)n3n- chains which run along the [110] and [110] directions, forming a sequence of double layers [Co2MF10]n3n-. The influence of the trivalent cation within the layers and between them on the magnetic behavior is demonstrated.

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Abstract The crystal structure of the compound Na-CuCrF7 (orthorhombic, a = 710.0, b = 1033.8, c = 751.8 pm, Z = 4) was refined in space group Pmnb to Rg= 0.028 (1545 independent reflections). The Jahn-Teller distortion of the CuF6 -octahedra (Cu-F = 191.1/193.8/212.4 pm. mean 199.1 pm) reduces the symmetry compared to the body-centered orthorhombic weberite type, to which it is otherwise closely related. The CrF6 -octahedra. interconnecting parallel chains of CuF6 -octahedra, are nearly undistorted (mean Cr-F = 190.6 pm). Na2CuFeF7 exhibits a supercell with a different structure (monoclinic, a = 2468.7, b = 734.7, c = 1245.2 pm, β = 99.29°, Z = 16). It may be interpreted as a new intermediate type between orthorhombic and trigonal weberites. Preliminary results obtained from refinement in space group A2/n (Rg = 0.076) are given and discussed (mean values Cu-F = 199 pm, Fe - F = 192 pm).