Synthesis and structure of the disordered modification of Pb7F12Cl2

We recently discovered a new compound with composition Ba7F12Cl2. It was po ssible to show that the variation of the synthesis conditions makes it poss ible to obtain a disordered and an ordered modification with different latt ice parameters and space groups (P6(3)/m [176] and P (6) over bar [174]). F or 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 crysta ls were grown from a flux and the structure was refined in the hexagonal sp ace group P6(3)/m to R(R-w) = 0.043(0.038) for 284 reflections and 26 param eters. Lattice parameters are a = b = 1021.90(8) pm and c = 361.93(6) pm wi th Z = 1. Propeller-type arrangements with chlorine as axis and fluorines a s blades are observed. The ordered modification of Pb7F12Cl2 was prepared b y a new hydrothermal synthesis. Differences between both modifications are found in the lattice constants and atomic occupation parameters for the ato m type Pb2 and the connected fluorine ions. (C) 2000 Academic Press.