Strukturen cäsiumhaltiger Fluoride, II¹ Die Kristall- und Magnetische Struktur von CsFeF₄ / Crystal and Magnetic Structure of CsFeF₄

Abstract

The results of an X-ray structure determination on single crystals of CsFeF 4 are reported. The compound crystallizes tetragonally with α = 7.79 4 , c = 6.55 3 Å, z = 4, in spacegroup P4/nmm-D 4h 7 and is a hitherto unknown superstructure variant of the TlAlF 4 -type. Cesium exhibits 12-coordination (mean value Cs-F = 3.25 Å); the FeF 6 -octahedra are characteristically shortened normal to the FeF 4⁻ -layers (Fe-F = 1.96 2 /1.86 1 Å). An improved model is proposed and verified for a related structure of RbFeF 4 , showing the same features. Neutron diffraction studies on powder samples of CsFeF 4 show that both compounds are identical as for their magnetic structures.