Search

Colorless crystals of the barium rare earth hydrogarnets Ba3[RE(OH)6]2 (RE = Sc, Y, Ho–Lu) were synthesized under hydroflux conditions with KOH at about T = 200 °C starting from the respective RE 2O3 and Ba (NO3)2. Single-crystal X-ray diffraction analysis on these distorted rhombic dodecahedra revealed the cubic space group Ia 3 ‾ $‾{3}$ d (no. 230). The crystal structures of the hydrogarnets Ba3[RE(OH)6]2 are discussed and compared with those of other hydrogarnets. The occurrence of additional reflections, which do not fulfill the reflection conditions of Ia 3 ‾ $‾{3}$ d, is analyzed and described by Renninger or λ/2 effects. A correlation is established between the space group adopted by a hydrogarnet and characteristic interatomic distances. In addition, single-crystal structure data of the strontium indium hydrogarnet Sr3[In(OH)6]2 are provided.

Yellow prismatic crystals of rubidium bromido-antimonate(III) Rb7Sb3Br16 and of two different modifications of thallium bromido-bismuthate(III) Tl7Bi3Br16 were obtained by solvent-free synthesis and by precipitation from acidic aqueous solutions. X-ray diffraction analyses revealed the Tl7Bi3I16-type for α-Tl7Bi3Br16 (orthorhombic, Cmcm, a = 2324.31(8) pm, b = 1346.69(4) pm, c = 3460.0(1) pm; Pearson symbol oC312) and a new structure type for β-Tl7Bi3Br16 (monoclinic, C2/c, a = 2331.87(5) pm, b = 1343.33(3) pm, c = 3546.01(7) pm, β = 102.708(1)°; mC312). The antimonate Rb7Sb3Br16 adopts the Tl7Bi3I16-type, too (orthorhombic, Cmcm, a = 2347.16(3) pm, b = 1357.89(5) pm, c = 3539.47(9) pm; oC312). The crystal structures of α- and β-Tl7Bi3Br16 comprise alternating slabs of isolated [BiBr6]3– octahedra and [Bi2Br10]4– octahedra pairs. Both structure types are hierarchically organized and can be regarded as sphere close packing with the same stacking sequence, if octahedra and octahedra pairs are replaced by spheres of equal size. The structural relationship between the Tl7Bi3I16-type and the hydrate Na7Bi3Br16 · 18H2O, which comprises similar structural features, is discussed.

The structural properties of modulated SrGe6− x (x≈0.45) were investigated by means of single-crystal and powder X-ray diffraction combined with quantum chemical calculations. The framework compound SrGe6− x adopts a defect variant of the EuGa2Ge4-type crystal structure. Samples of the binary compound with nominal compositions 0≤x≤0.5 were synthesized at pressures from 5 to 6 GPa and a temperature of typically 1400 K. The product reveals diffraction peaks of the EuGa2Ge4-type subcell plus additional reflections indicating an ordered superstructure. Detailed crystal structure analysis evidences the incommensurate nature of the superstructure and a modulation of the vacancy ordering in the germanium network. The computations have shown that the non-stoichiometric composition of the framework with its local defect organization affects the calculated charge of the strontium anions. Although the chemical composition is close to a charge-balanced situation, temperature-dependent resistivity measurements showed metal-type conductivity. At ambient pressure SrGe6− x decomposes exothermally and irreversibly at T=680(10) K into SrGe2 and germanium, indicating its metastable nature at ambient pressure.

A new calcium iron ruthenium hydrogarnet with the approximate composition Ca3(Ru2− x Fe x )(FeO4)2− y (H4O4)1+ y (x=1, y≈0.35) has been obtained by hydrothermal synthesis under oxidizing alkaline conditions. The compound crystallizes in the cubic space group Ia3̅d (No. 230) with a lattice parameter of a=12.4804(4) Å (T=100 K) and Z=8. The octahedral site of the garnet structure is equally occupied by Ru and Fe, whereas the tetrahedral site is partially occupied by Fe only. A partial substitution of the oxide anions by hydroxide ions is necessary for charge balancing, corresponding to the so-called hydrogarnet defects. The presence of hydroxide groups is proven by infrared spectroscopy. 57Fe Mössbauer spectroscopic data provide evidence for two different Fe3+ coordination environments as well as a magnetic ordering of two iron substructures with the respective ordering temperature above room temperature. The crystal composition was verified by energy-dispersive X-ray spectroscopy and the thermal behavior of the calcium iron ruthenate was studied by difference thermal analysis.

The ternary lanthanum sulfide selenide β -LaS1.86(1)Se0.14(1) was obtained by reaction of the elements in an NaCl flux. The new compound adopts the β -LnS2 structure type and crystallizes in the orthorhombic space group Pnma (no. 62) with lattice parameters of a = 814.77(1), b = 1638.46(1) and c = 413.88(1) pm. Raman lines indicate the presence of mixed (S1−ySey)2− dianions with y ≈ 0.14, besides the well known S2 2− dianions. The band gap of β -LaS1.86(1)Se0.14(1) is 2.5 eV as determined by optical spectroscopy.

A series of rare-earth metal disulfides LnS2 and diselenides LnSe2 (Ln = Sm, Gd, Tb, Dy, Ho, Er and Tm has been prepared by high-pressure high-temperature synthesis at 8(1) GPa. The dichalcogenides LnX 2 (X = S, Se) are found to crystallize in the α-LaS2 type with the monoclinic space group P121/a1 (no. 14). The crystal structure is a twofold superstructure of the ZrSSi aristotype and consists of puckered cationic [LnX]+ double slabs which are sandwiched by planar chalcogen sheets containing X 2 2– dumbbells.

α-CeS2 and α-NdS2 were obtained by a metathesis reaction of the anhydrous trichlorides LnCl3 (Ln = Ce, Nd) and Na2S2 at 1070 K. The two compounds adopt a monoclinic structure type, the so-called CeSe2 or α-type of the rare earth metal dichalcogenides (space group P21/a), with lattice parameters of a = 8.105(3), b = 4.075(1), c = 8.097(3) Å, β = 90.03(4)◦ for CeS2 and a = 8.008(2), b = 4.019(1), c = 8.032(2) Å , β = 90.00(3)◦ for NdS2. Single crystals of β -LaS2, β -CeS2 and β -PrS2 were obtained as by-products in the syntheses of the ternary copper sulfides CuLnS2 by reacting the elemental educts (Cu, S and Ln = La, Ce, Pr) in a CsCl flux at 970 K. These compounds adopt the orthorhombic β -LaS2 structure type (space group Pnma) with lattice parameters of a = 8.140(1), b = 16.379(1), c = 4.144(1) Å for β -LaS2, a = 8.068(1), b = 16.216(1), c = 4.095(1) Å for β -CeS2, and a = 8.044(1), b = 16.160(1), c = 4.073(1) Å for β -PrS2

An incommensurately modulated structure of CeSi1.82 as determined by single-crystal X-ray diffraction at room temperature is reported. The observed satellite reflections reduce the orthorhombic symmetry of the X-ray pattern to a monoclinic one. This suggests the description of the modulated structure in the monoclinic superspace group I2/b(αβ0)00. The modulation wave vector was determined to q = 0.410(1) · a* + 0.610(1) · b*. The refinement was done using harmonic modulation functions for the displacement and the occupation probability of the atoms, the quality parameters converged to R obs = 3.33% (R obs = 2.56% for the main reflections, R obs = 8.88% for the 1st order satellite reflections and R obs = 33.06% for the 2nd order satellite reflections). The origin of the observed satellite reflections is attributed to a modulation of the partly occupied Si site caused by composition changes within the crystal.