The title compound, hexabarium lead(II) decafluoride dichloride, is a solid solution in the system Pb 7 F 12 Cl 2 -Ba 7 F 12 Cl 2 and crystallizes isotypically with the ordered modification of the parent compounds in the space group P6. The coordination polyhedra of the three different metal sites are distorted tricapped trigonal prisms with F 7 Cl 2 coordination sets for two of these sites (Wyckoff positions 3k and 3j, each with site symmetry m..), and the remaining site being exclusively coordinated by fluoride ions (1a, 6..). By sharing faces, a threedimensional structure is accomplished. The three metal sites have remarkably different occupancies by the two types of metal ions. Whereas the site on the 3k position shows only a minor incorporation of Pb 2+ [occupancy ratio Ba:Pb = 0.93 (4):0.07 (4)], the 3j site shows the highest amount of incorporated Pb
Structure descriptionThe current study provides indications as to which of the three metal sites of the Ba 7 F 12 Cl 2 structure is preferentially substituted in solid solutions of the type Ba 7-x M x F 12 Cl 2 (M = divalent metal with ionic radius comparable to Ba 2+ ) and hence could help to better understand spectroscopic data of europium-doped Ba 7 F 12 Cl 2 phosphors (Hagemann et al., 2015). The isotypic ordered parent phases Pb 7 F 12 Cl 2 and Ba 7 F 12 Cl 2 were first reported by Aurivillius (1976) and Es-Sakhi et al. (1998), respectively. For a review of crystal-chemical peculiarities in the system BaF 2 /BaCl 2 , including the ordered (space group P6) and disordered modifications (space group P6 3 ) of Ba 7 F 12 Cl 2 , see: Hagemann et al. (2012). The crystal structure of the title compound is shown in Fig. 1 The mixture was placed in a teflon container (capacity 10 ml) which was two-thirds filled with water. The container was closed with a teflon lid and placed in a steel autoclave at 493 K for one week. Colourless crystals with a needle-like form were obtained from the mother liquor by filtration. Unit-cell determination of several selected crystals with subsequent least-squares refinements of the lattice parameters revealed nearly identical unit cells, indicating that the composition of the grown crystals was consistent and very similar to that of the title compound.
RefinementThe three M 2+ sites are occupied by both Ba and Pb. For the final model, the three metal sites were constrained to be fully occupied. Each of the sites was refined with common coordinates and displacement parameters for the two types of metals. The highest and lowest remaining electron density peaks are found 2.08 and 0.16 Å , respectively, from the M1 site. The crystal measured was twinned by inversion with an approximate ratio of the twin domains of 1:1 [Flack parameter 0.55 (5)]. Crystal data, data collection and structure refinement details are summarized in Table 2.