Strukturen caesiumhaltiger Fluoride. VIII. Cs7Ni4F15 und Cs7Co4F15: Die Kristallstrukturbestimmung an den bisher caesiumreichsten Verbindungen in den zugehörigen Systemen CsF/MF2

Structures of Cesium-containing Fluorides. VIII. Cs₇Ni₄F₁₅ and Cs₇Co₄F₁₅: Crystal Structure Determination of the Hitherto Cesium-richest Compounds in the Corresponding Systems CsF/MF₂ . The only nickel-containing phase we could identify after solid state reaction 2 CsF + NiF₂ was the compound Cs₇Ni₄F₁₅. The single crystal structure determination of this monoclinic fluoride (and its cobalt analog Cs₇Co₄F₁₅) yielded a = 787.2 (788.3), b = 1089.7 (1096.6), c = 1149.5 (1164.9) pm, β = 92.74 (92.59)°, space group P2₁/c, Z = 2, R_g = 0.045 (0.058) for 2543 (2716) independent reflections. The resulting strongly puckered layer structure rather than of single octahedra consists of face-sharing M₂F₉ units, which are connected via the half of their remaining corners. The M? F distances vary from 195.1 to 212.0 (196.7 to 217.0) pm and show unusual high mean values of 203.7 (206.5) pm. Data for comparison and further details are discussed.