Synthesis and Structure of the Disordered Modification of Pb7F12Cl2

We recently discovered a new compound with composition Ba7F12Cl2. It was possible to show that the variation of the synthesis conditions makes it possible to obtain a disordered and an ordered modification with different lattice parameters and space groups (P63/m [176] and P6 [174]). For Pb7F12Cl2 an ordered modification is reported in the literature. In this paper we present the synthesis and structural characterization from X-ray diffraction data of the disordered modification of Pb7F12Cl2. Single crystals were grown from a flux and the structure was refined in the hexagonal space group P63/m to R(Rw)=0.043(0.038) for 284 reflections and 26 parameters. Lattice parameters are a=b=1021.90(8) pm and c=361.93(6) pm with Z=1. Propeller-type arrangements with chlorine as axis and fluorines as blades are observed. The ordered modification of Pb7F12Cl2 was prepared by a new hydrothermal synthesis. Differences between both modifications are found in the lattice constants and atomic occupation parameters for the atom type Pb2 and the connected fluorine ions.