Polymorphie von Cs2NaMnF6. Die Kristallstrukturen der Hochdruck- und der Hochtemperaturmodifikation

Polymorphism of Cs₂NaMnF₆. Crystal Structures of the High Pressure and the High Temperature Phase Cs₂NaMnF₆ has been prepared in three polymorphous forms and investigated by X-ray diffraction. Under high pressure (> 5 kbar) a cubic α-phase was formed with elpasolite structure (space group Fm3m, a = 876.2 pm, Z ? 4, R ? 0.045 for 12 powder reflections). By quenching from 700°C a high temperature γ-form could be trapped with 12L-Cs₂NaCrF₆ structure (space group R¯3m, Z = 6, R_w ? 0.041 for 419 independent single crystal reflections). The “normal” β-phase is a low symmetric variant of this 12L-type. The influence of the Jahn-Teller effect on the structures and the polymorphism is discussed.