Uber hexagonale Perowskite mit Kationenfehlstellen. VI. Strukturbestimmung an Ba8Re2W3□3O24 – der ersten hexagonalen Perowskitstapelvariante vom 24 L-Typ

On Hexagonal Perovskites with Cationic Vacancies. VI. Structure Determination on Ba₈Re₂W₃□₃O₂₄ – the First Hexagonal Stacking Polytype with 24 Layers For the hexagonal stacking polytype of rhomboedral 24 L type, Ba₈Re₂W₃□₃O₂₄, eight sequences are possible: (6)(2); (4)1(2)1; (5)1(1)1; (5)(3); (3)11(1)11; (1)21(1)12 (all space group R3m) and 4211; 3221 (all space group R3m). By vibrational spectroscopic investigations the sequences (6)(2); (5)(3) and 4211 could be eliminated. By means of intensity calculations the sequence (1)21(1)12 or chhhhchh respectively can be selected out of the remaining five. The structure contains groups of three and five face-connected octahedra which are linked with another by common corners. In the ideal structure, vacant lattice sites are found in the centres of the second and fourth octahedra of the block of five face-sharing octahedra and in the central octahedron of the block of three face-sharing octahedra. The remaining positions are occupied by the Re and W atoms. According to this distribution an direct contact of occupied face-sharing octahedra is absent. In the real structure, lattice defects are introduced by partial redistribution of atoms between occupied and vacant lattice positions in the blocks of three and five face-sharing octahedra. The occupation factor of one vacancy is about 8%. The refined, intensity related R′ value is 15.2%.     

Über Ordnungs-Unordnungsphänomene bei Sauerstoff perowskiten vom Typ A2+3B2+M5+2O9

Perovskites of the type A²⁺₃B²⁺M⁵⁺₂O₉, where A²⁺ = Ba, Sr; B²⁺ = Mn, Co, Ni, Zn; M⁵⁺ = Nb, Ta, show order-disorder phenomena. At lower temperatures a thermodynamically unstable disordered cubic perovskite is formed ($\text{1}\text{3}$ formula unit—$\text{AB}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{M}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$—in the cell), which transforms irreversibly into a 1: 2 ordered high-temperature form with 3L structure (sequence (c)₃). For A²⁺ = Ba this lattice is hexagonal (space group $\text{P}\text{3}\text{m1}$; one formula unit in the cell); with A²⁺ = Sr a triclinic distortion is observed. For Ba₃CoNb₂O₉ a second transformation into a cubic disordered perovskite takes place at 1500°C. This transition is reversible and of the order-disorder type. The vibrational and diffuse reflectance spectra are discussed.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXIV. Rhomboedrische 9 L-Stapelvarianten in den Systemen Ba3W M □ O9−x/2□x/2 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XXIV. Rhombohedral 9 L Stacking Polytypes in the Systems Ba₃W M □O_9?x/2□_x?2 with M^V = Nb, Ta In the system Ba₃WNb□O_9?x/2□_x/2 stacking polytypes of rhombohedral 9 L type (sequence (hhc)₃; space group R3 m) can be prepared with ～1/3 ? × ? 2. For x = 2(Ba₃Nb₂□O₈□) two modifications are formed. In the corresponding Ta system the phase with is reduced to a smaller region with x ? 1/3.     

Über hexagonale Perowskite mit Kationenfehlstellen. XVI Die rhomboedrischen 12 L-Stapelvarianten Ba3AIIIM□O12 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XVI. Rhombohedral 12 L-Stacking Polytypes Ba₃A^IIIM □O₁₂ with M^V = Nb, Ta The white quaternary oxides Ba₃LaM□O₁₂ with M^V = Nb, Ta belong to the group of hexagonal perovskites with cationic vacancies. They crystallize in a rhombohedral 12 L-structure (sequence (hhcc)₃; space group R3 m) with a = 5.75₁ Å; c = 28.1₁ Å (M^V = Nb); a = 5.74₆ Å; c = 28.2₀ Å (Ta) and Z = 3. Signs for the formation of isotypic compounds with A^III = Pr, Nd could be obtained as well.     

Über Perowskite Ba2BBTeVIO6

On Perovskites Ba₂B B Te^VIO₆ Compounds of composition Ba₂BBTe^VIO₆ with B^I = Li, Na; B^III = La, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Yb, Y, In, Sc crystallize in a cubic 1:1 ordered perovskite structure. The vibrational spectroscopic investigations show, that more species of TeO₆ octahedra are present in the lattice.     

Evolutionary chemistry approach toward finding novel inhibitors of the type 2 diabetes target glucose-6-phosphate translocase

A genetic algorithm (GA), driven by experimentally determined biological activities as a feedback fitness function, was used to propose novel small molecules as inhibitors of glucose-6-phosphate translocase (G6PT) in iterative rounds of evolutionary optimization. A straightforward polymer-supported synthetic sequence was implemented to synthesize molecules proposed by the GA, and the biological activities of the compounds were determined by a microsomal assay. Additional compound design strategies were integrated, such as Tanimoto similarity-based selection of starting materials and transfer of favored structure elements into a new chemical scaffold to identify more active and selective inhibitors.     

Über gemischtvalente Ruthenium-Perowskite Ba3B3+Ru24,5+O9 – zur katalytischen Aktivität von Sauerstoffperowskiten mit vier- und fünfwertigen Edelmetallen

On Mixed Valent Perovskites Ba₃B³⁺Ru₂^4,5+O₉ – Catalytic Activity of Perovskite Oxides with Noble Metals The black compounds Ba₃B³⁺Ru₂O₉ crystallize with B³⁺ = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y in a hexagonal BaTiO₃ structure (6 L, sequence (hcc)₂) with an ordered distribution (1:2 order) of B³⁺ and ruthenium (BO₆ single octahedra; Ru₂O₉ double groups). The mean oxidation state of ruthenium is about +4.5. The properties are compared with that of other isotypic stacking polytypes Ba₃B³⁺M₂^4,5O₉ (M₂ = IrRu, Ir₂, PtRu) and Ba₃B²⁺M₂⁵⁺O₉ (M = Ru, Ir). The results of activity tests concerning the efficiency of perovskite oxides with noble metals in respect of the oxidation of CO or CH_x and the reduction of NO_x are reported.     

Über Perowskitphasen in den Systemen BaO–SE2O3–UO2,x mit SE = Seltene Erden,La und Y. I. Verbindungen der Zusammensetzung Ba2SE0,67UO6 und Ba2SE0,67UO5,5

In the BaO–SE₂O₃–UO_2,x-system the formation of the polymorphic ordered perovskites Ba₂SE_0,67UO₆ ist observed. At the reduction of the former the ordered perovskites Ba₂SE_0,67UO_5,5 are formed, which contain U(V) only. According to the results of the magnetic and spectroscopic investigations the pentavalent uranium occupies the centers of slightly or strongly distorted octahedrons, while U(VI) is partly forming UO-groups. The rare earths are always present in the trivalent state. – The structural relations to the ordered perovskite A₂BB′O₆ are discussed.     

Perovskite Phases in the Systems AIIO–UVIO3. II. On The System ABIIUVIO6, with AII,BII = Ba,Sr, Ca

Studies on the system AB^IIU^VIO₆ with A^II, B^II = Ba, Sr, Ca or combinations of these have shown that the alkaline earth ions cannot substitute each other in all proportions. The perovskites were studied by X-ray diffraction and vibrational spectroscopic methods. The lattice vibration region of the far infrared spectra proved to be of particular value in providing information on the occupancy of the A and B sites. Analysis of the spectra shows that, in the majority of cases, contary to the geometrical predictions some of the larger alkaline earth ions occupy the six-coordinated B sites and some smaller ions the A positions. The number of ions that take in this A ? B site-exchange can amount to 20%, but in normally smaller.