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Zur Struktur der Kupfer-Weberite Na 2 CuCrF 7 und Na 2 CuFeF 7 / Concerning the Structures of the Copper Weberites Na 2 CuCrF 7 and Na 2 CuFeF 7

1988; De Gruyter; Volume: 43; Issue: 6 Linguagem: Inglês

10.1515/znb-1988-0610

1865-7117

S. Kummer, Werner Massa, D. Babel,

Muon and positron interactions and applications

Abstract The crystal structure of the compound Na-CuCrF 7 (orthorhombic, a = 710.0, b = 1033.8, c = 751.8 pm, Z = 4) was refined in space group Pmnb to R g = 0.028 (1545 independent reflections). The Jahn-Teller distortion of the CuF 6 -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 CrF 6 -octahedra. interconnecting parallel chains of CuF 6 -octahedra, are nearly undistorted (mean Cr-F = 190.6 pm). Na 2 CuFeF 7 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 (R g = 0.076) are given and discussed (mean values Cu-F = 199 pm, Fe - F = 192 pm).