Struktur und Bindung in Übergangsmetall-Fluoriden MIIMeIVF6 A. Phasenübergänge

Structure and Bonding in Transitition Metal Fluorides M^IIMe^IVF₆ A. Phase Transitions A summary outline of the structure types of all compounds M^IIMe^IVF₆ known so far is given. Compounds with a 3d transition metal ion in the M^II site crystallize in the cubic ordered ReO₃ lattice and the hexagonal LiSbF₆ structure. For cations with a Jahn- Teller unstable E_g ground state we have found a symmetry reduction to tetragonal and triclinic variants of those two lattice types in addition. Phase transitions between the different structures could be observed by Guinier techniques in the temperature range 80 K < T < 800 K in many cases. The relative stability of the hexagonal low temperature phases in comparison to the cubic high temperature modifications is extensively discussed on the basis of geometric parameters and the electronic properties of the Me^IV and M^II ions. Quite a number of compounds M^IIMe^IVF₆ was prepared and characterized for the first time. The results of the spectroscopic investigation will be published later.