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The compound Ba5I2O12 was synthesized by heating a precipitate of dissolved Ba(OH)2·8H2O and H5IO6. Rb2O was added to increase the crystallite size. The crystal structure was determined from conventional laboratory X-ray diffraction data by using a real-space structure solution approach followed by a Rietveld refinement. No constraints on positions were used. The structure analysis gave an orthorhombic symmetry with a = 19.7474(2) A, b = 5.9006(1) A and c = 10.5773(1) A. The final RBragg value in space group Pnma (62) was 1.0 %. The structure can be described by layers of a metal and iodine arrangement forming almost pentagonal holes. Raman measurements were correlated with the two IO6 octahedra. Two further barium periodate patterns were observed and indexed.

A series of mixed crystals with general formula Ba7-xNayF12Cl2-zBrz in the ordered modification (space group P-6) has been studied by single crystal x-ray diffraction. Depending on synthesis conditions, the disorder in the channels (i.e. occupation of 0 0 z sites) can be changed. The disorder is found to be correlated with the refined Na content, and its effect on Ba-Cl(Br) bond length is discussed.

Crystals of the chemical composition Ba7F12Cl2 were modified by adding a small amount of Ca2+ to allow the synthesis of the corresponding bromine compound Ba[Ca]7F12Br2. These samples were prepared in a NaBr flux and characterized by single crystal x-ray diffraction. The new structure crystallizes in a disordered arrangement in the hexagonal space group P63/m (176). The calcium ion has a coordination number of 6. Solid solutions on the heavy halide position can be synthesised in a NaCl/NaBr flux to obtain the compounds Ba7-xCaxF12(ClyBr1-y)2 with x = 0.5 and 0 < y < 1. Regardless the amount of calcium used in the preparation process, the Ca stoichiometry in the compound is always between 0.3 and 0.5. The lattice parameters differ depending on the Ca- and Br-content between 1053.81(5) a = b 1058.93(3) pm and 421.21 c 426.78(3) pm.

Crystals of ordered and disordered Ba7F12Cl2 were prepared by flux growth and solid state reactions. These new structures were characterized by single crystal and powder X-ray diffraction. The disordered variant which shows disorder on one of the cation sites was obtained from a BaF2 + BaCl2 + NaCl/NaF flux. It has hexagonal space group P63/m (176) with one formula unit per unit cell. The lattice constants are a = b = 1059.55(5) pm and c = 420.10(4) pm (at 21 °C). The structure was refined to R(Rw) = 0.026(0.030) for 346 independent reflections and 26 parameters. Slow cooling of a mixture of BaF2 and LiCl yields the ordered variant. This one crystallizes in the hexagonal space group P6 (174) with one formula per unit cell. Lattice constants at 21 °C are a = b = 1063.46(2) pm and c = 417.52(1) pm. The structure was refined to R(Rw) = 0.017 (0.017) for 638 independent reflections and 45 parameters. The structural arrangement and the interatomic distances of the two variants are mutually similar. The barium atoms have coordination number nine. Propeller-type arrangements with a chloride ion on the axis and the fluoride ions as blades are observed. These latter ones are interconnected into channels' of tricapped fluoride prisms. Occupation disorder of the barium sites in the channels of the disordered variant makes the main difference between the two. An unexpectedly high X-ray density obtained for both variants of Ba7F12Cl2 can be correlated to the density of other barium fluorohalides having a coordination number of nine for the barium ion.

Crystals of ordered Ba6EuF12Cl2 were found to form during high temperature flux growth. The structure was refined in the hexagonal space group P6 to RF(RF w) = 0.024(0.024) for 326 reflections and 46 parameters. Lattice parameters are a = b = 1059.27(8) pm and c = 416.36(2) pm; Z = 1. The structure is isotypic to Ba7F12Cl2. No solid solution of Ba/Eu was observed, the Eu2+ ions are located in the channels formed by 3 + 6 fluorine ions, occupying only one of the three metal sites of the Ba7F12Cl2 structure.