Verfeinerung der Kristallstrukturen von K2ZnF4 und K3Zn2F7*

Abstract

Abstract The layer structures of the ternary fluorides K2ZnF4 (a = 405.8 pm, c = 1310.9 pm) and K3Zn2F7 (a = 406.0 pm, c = 2117.1 pm), both crystallizing in the tetragonal space group I4/mmm, have been refined using single crystal data. They are representatives of the K2NiF4- and the Sr3Ti2O7-type, resp. No significant distortion of octahedra was found in K2ZnF4. A small shortening of the terminal Zn–F bond (200.7 pm) in K3Zn2F7 is mainly due to an off-center location of the zinc cations. The reason for this is discussed along with the special features of the 9-coordination of potassium in both structures. Mean values Zn–F = 202.8 pm and K1−F = 280.7 pm are the same in K2ZnF4 and K3Zn2F7. K2–F = 286.1pm is the average value found for the slightly distorted cuboctahedral 12-coordination of the additional potassium in the latter compound.