The Crystal Structures of the High‐temperature Phases of Ag4Mn3O8

Two endothermic, reversible structural phase transitions of first order have been observed in Ag₄Mn₃O₈ by means of in‐situ powder diffraction and by differential scanning calorimetry. At a temperature of T = 477 K, Ag₄Mn₃O₈ undergoes a structural phase transition from the room temperature phase in space group P3₁21 to a phase in space group R32, and at T = 689 K a second phase transition to a structure in space group P4₃32 occurs. Whilst the Mn₃O₈ framework does not change significantly upon heating, rearrangements of the silver atoms, located in the cavities of the framework, were found to be the driving force behind the transitions. The structural changes with increasing temperature proceed along a path of minimal group‐supergroup relations between the respective space groups.     

X-ray Diffraction Study of Phases in the System CaS-Lu2S3 (0–50 mol % Lu2S3)

Thirteen samples were synthesized in the system CaS-Lu₂S₃ in the range 0-50 mol % Lu₂S₃ and studied by X-ray powder diffraction (phase analysis, determination and refinement of unit cell parameters, Rietveld structure refinement). The phases crystallizing in the system have NaCl-type structures (space group Fm3m, unit cell parameter a ₀) with a cubic, hexagonal, or orthorhombic superstructure, the respective structure types being Yb_0.875S (space group F4?3m, a~ 2a ₀), CaY₂Se₄ (space group $R?erline 3m, {∈xt a ¡m {a_0}sqrt 2}, {∈xt c ¡m 2{a_0}sqrt 3}$), and Tm_0.76Se (space group Pnnn; $a ¡m {a_0}sqrt 2, {∈xt b ¡m {a_0}sqrt 2}, {∈xt c ¡m 2{a_0}}$), and a phase with a Yb₃S₄-type orthorhombic unit cell (space group Pnma).     

Infrared spectroscopy and the structure of rare-earth chromium borates RCr<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> (R = La-Er)

Rare-earth chromium borates RCr₃(BO₃)₄, where R = La-Er, obtained as a result of spontaneous solutionmelt crystallization and belonging to two polytypic modifications (R32 (D₃⁷) and C2/c (C _2h ⁶) space groups) are studied by infrared spectroscopy with the factor group analysis of vibrations. Borates with R = La-Nd are shown to crystallize in the monoclinic C2/c space group. Borates with R = Sm-Er in the 1:1 ratio of batch and solvent form rhombohedral (R32 space group) and monoclinic (C2/c space group) phases at the 2.3:1 ratio, except EuCr₃(BO₃)₄ and GdCr₃(BO₃)₄ that have the rhombohedral structure under all crystallization conditions. Both rhombohedral and monoclinic polytypes may contain oppositely ordered layers. Y-, Tm-, Yb-, Lu-chromium borates are not formed.     

Two forms of aluminium phosphate tridymite from X‐ray powder data

Monoclinic and triclinic (pseudo‐orthorhombic) AlPO₄ tridymites have been refined from X‐ray powder diffraction data using the silica analogues as starting models. The framework structures of both forms of tridymite are made up of six‐membered rings of tetrahedra which differ in the distortion patterns of the ring shapes. Ordered occupation of alternate tetrahedra by Al and P leads to a doubling of the a lattice parameter for monoclinic AlPO₄ tridymite (space group Pc) and loss of the C‐centring with respect to the isotypic silica tridymite (space group Cc). Triclinic AlPO₄ tridymite was refined in the same space group (F1) as the SiO₂ analogue.     

Phase transitions and twinned low‐temperature structures of tetraethylammonium tetrachloridoferrate(III)

The title compound, [(C₂H₅)₄N][FeCl₄], has at room temperature a disordered structure in the high‐hexagonal space group P6₃mc. At 230 K, the structure is merohedrally twinned in the low‐hexagonal space group P6₃. The volume has increased by a factor of 9 with respect to the room‐temperature structure. At 170 and 110 K, the structure is identical in the orthorhombic space group Pca2₁ and twinned by reticular pseudomerohedry. The volume has doubled with respect to the room‐temperature structure. All three space groups, viz. P6₃mc, P6₃ and Pca2₁, are polar and the direction of the polar axis is not affected by the twinning. In the P6₃ and Pca2₁ structures, all cations and anions are well ordered.     

Kristalldaten von einigen Alkalihalogeno-auraten(III)

The lattice dimensions of the monoclinic unit cells of the compounds CsAuCl₄, CsAuBr₄, RbAuCl₄, and RbAuBr₄ were determined by means of single crystal X-ray diffraction photographs. The three first mentioned compounds are isostructural(space group I2/c). RbAuBr₄ has a different space group (P2₁/a) but a closely related crystal structure.     

Die Kristallpackung in drei Modifikationen von PPh4[ReO(S4)2] und PPh4[ReS(S4)2]

The Crystal Packing in three Modifications of PPh₄[ReO(S₄)₂] and PPh₄[ReS(S₄)₂] Mixed crystals PPh₄[ReS(S₄)₂]_0,63[ReO(S₄)₂]_0,37 were obtained from PPh₄Cl, ReCl₅ and Na₂S₄ in acetonitrile. Their crystal structure corresponds to the known structure of this kind of compound (space group P2₁/n). In a similar reaction with ReBr₅ instead of ReCl₅, PPh₄[ReO(S₄)₂] was obtained in small yield. Its triclinic crystal structure was determined by X‐ray crystallography (space group P1). It contains cation pairs (PPh₄⁺)₂ such as they have been found in many other instances. In contrast, the crystal structures of the mixed crystals and of one known modification of PPh₄[ReS(S₄)₂] have PPh₄⁺ columns similar to compounds crystallizing in the space group P4/n, albeit in a severely distorted manner; their space group P2₁/n is a subgroup of P4/n with a doubled unit cell. In another modification of PPh₄[ReS(S₄)₂] (space group P2₁/c) the columns are less distorted, but arranged in a different way.     

Cs[Ag4Zn2(SCN)9]

Caesium tetrasilver dizinc nona­thio­cyanate, Cs[Ag₄Zn₂(SCN)₉], forms a continuous structure, where the Ag atoms and the S atoms of the thio­cyanate groups form chains which run along [101]. These chains are bonded together through the Cs and Zn atoms. It is not possible to distinguish between space groups P1 and P, but, if the latter space group is correct, the structure contains a thio­cyanate group disordered across a centre of inversion. The structure is described in space group P, in which the Cs atom also lies on a centre of inversion.     

Crystal structures and polymorphism in compounds Bi6+xT1−xP2O15+y, T=first row transition metals and Pb

The compounds Bi_6+xT_1−xP₂O_15+y, T=Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb display five polymorphic forms. Polymorph A is formed by the Ti, Mn, Fe and Ni phases. Polymorph B is exhibited by Co and Cu compounds. The Cr phase crystallizes as polymorphic form C and the Zn phase crystallizes as polymorph D. The Pb compound crystallizes in a new structure type designated as polymorph E. The transition metal crystal structures demonstrate a similar motive. OBi₄ tetrahedra share edges to form two-dimensional Bi₂O₂ layers that are spanned by PO₄ tetrahedra and TO_6−y octahedra, pyramids and a trigonal bipyramid to form a three-dimensional network. Polymorph A crystallizes in space group C2; polymorph B is centrosymmetric with space group C2/c, the unit cell parameters differ and the unit cell volume is about double. Polymorph C crystallizes in space group and polymorph D exhibits space group C2. Bi_6.4Pb_0.6P₂O_15.2 can be considered as polymorph E, space group C2, with a new crystal structure but related stoichiometry.     

Thermal and dielectric properties of LiKSO4 and LiCsSO4

Measurements of the thermal and dielectric properties of single crystals of the double sulfates LiKSO₄ and LiCsSO₄ are reported. Uncertainty in the determination of the space group of LiCsSO₄ is resolved on the basis of optical second harmonic generation and pyroelectric measurements; the correct space group is Pcmn. Measurements of the pyroelectric coefficient, dielectric constant, and specific heat of LiKSO₄ permit an assessment of the suitability of this material for use in pyroelectric detectors.     

Two reversible enantiotropic phase transitions in a pentacoordinate silicon complex with an O,N,O′‐tridentate valinate ligand

Dimethyl[N‐(4‐oxidopent‐3‐en‐2‐ylidene)valinato‐κ³O,N,O′]silicon(IV), C₁₂H₂₁NO₃Si, (II), crystallizes in the orthorhombic space group P2₁2₁2₁. The chiral compound undergoes two sharp enantiotropic phase transitions upon cooling. The first transformation occurs at 163 K to yield a unit cell with one axis having double length. This intermediate‐temperature form has the monoclinic space group P2₁. The second transition takes place at 142 K and converts the single crystal into the low‐temperature form in the orthorhombic space group P2₁2₁2₁. This transition proceeds under tripling of the a axis of the high‐temperature form. Both phase transitions are fully reversible and correspond to order–disorder transitions of the isopropyl group of the valine unit in the ligand backbone. The phase transitions presented here raise questions, since they do not fit into the rules of group–subgroup relationships.     

Solid State Structures of AsCl5 and SbCl5

Arsenic pentachloride has a trigonal bipyramidal structure in the solid state with As‐Cl_eq = 210.6, 211.9 pm, As‐Cl_ax= 220.7 pm, space group Pmmn, a = 706.2 (1); b = 760.3 (2), c = 623.3 (1) pm. Antimony pentachloride exists in two modifications: above −54.1 °C it is also trigonal bipyramidal with Sb‐Cl_eq = 227.0 and Sb‐Cl_ax = 233.3 pm, space group P6₃/mmc, a = 741.4 (1), c = 799.0(2)pm. Below −54.1 °C it changes reversibly into a double chlorine bridged dimer resulting in an edge shared double octahedral structure, space group P2₁/c, a = 952.4 (1), b = 1189.9 (1), c = 1219.7 (1) pm, β = 108, 27 (1): In presence of water the formation of AsCl₅ is hindered, two salts containing the octahedral anion AsCl₆⁻ have been isolated, [(H₅O₂⁺)₅AsCl₆⁻(Cl⁻)₄], space group C2/c, a= 1416.9 (2), b = 1316.6 (3), c = 1215.3 (2) pm, β; = 94.96 (1)°, and [(H₅O₂⁺)(AsCl₆⁻)·AsOCl₃], space group P2₁/n, a = 771.6 (3), b = 904.5 (3), c = 2140.7(2)pm, β = 100.21(1). The AsOCl₃ moiety in this compound appears as a monomer, in contrast to pure AsOCl₃, which is a doubly oxygen bridged dimer in the solid state.     

Symmetry of (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript> crystals (R = Gd,La; M = W,Mo)

Kinetic order-disorder phase transitions (space group space group $ I\bar 4 $ I\bar 4 ↔ space group I4₁/a) have been considered for nonactivated and activated scheelite compounds (Na_0.5Gd_0.5)WO₄ (NGW), (Na_0.5Gd_0.5)MoO₄ (NGM), (Na_0.5La_0.5)WO₄(NLW), and (Na_0.5La_0.5)MoO₄ (NLM) synthesized by the Czochralski method and structural and growth sources of crystal dissymmetrization have been suggested. For NGW, it was shown that an increase in the difference between the content of Gd and Na in two positions of the structure with space group $ I\bar 4 $ I\bar 4 and their ratio leads to an increase in the deviation from centrosymmetry. On the basis of available literature data and our results, it was demonstrated that the degree of order depends on the initial composition of the reaction mixture, crystal growth and cooling rates, activator concentrations, and postgrowth treatment conditions. The inconsistency between X-ray diffraction data and asynchronous second harmonic generation studies was explained by the possibility of formation of centrosymmetric superstructures and/or local ordering of atoms.     

High‐ and low‐temperature La2RuO5 by powder neutron diffraction

The structure of dilanthanum ruthenium pentoxide was solved by powder neutron diffraction at room temperature and 1.5 K. High‐temperature La₂RuO₅ crystallizes in the monoclinic space group P2₁/c. Upon cooling, the sample undergoes a phase transition to the triclinic low‐temperature form (space group P). This transition leads to pronounced changes in the Ru—O—Ru bond distances, resulting in a dimerization of the ruthenium ions.     

Enantiomerically pure and racemic dimethyl{N‐[(2‐oxidonaphthalen‐1‐yl‐κO)methylidene]valinato‐κ2N,O}tin(IV)

The title compound, [Sn(CH₃)₂(C₁₆H₁₅NO₃)], crystallized from one reaction batch with high enantiomeric excess as both a pure enantiomer and a racemate. The S enantiomer crystallizes in the chiral space group P3₂. The racemate crystallizes in the space group P with R and S enantiomers in the crystal lattice; these form dimers about a crystallographic inversion centre.     

ChemInform Abstract: The Crystal Structures of Ni3+xSn4Zn and Ni6+xSn8Zn and Their Structural Relations to Ni3+xSn4, NiSn and Ni5‐δZnSn4.

Two new compounds, Ni_3+xSn₄Zn (x≈1.35, monoclinic, space group I2/m, Z = 2, single crystal XRD) and Ni_6+xSn₈Zn (x≈1.35, monoclinic, space group C2/m, Z = 2) are prepared by solid state reaction of the elements (Al₂O₃ crucible in evacuated quartz tubes, 1453 K).     

Two for the price of one – Resolvable polymorphism in a ‘single crystal’ of α- and β-Sb3O4I

The title compound forms as biphasic single crystals containing the α- and β-polymorphs. The structure of both polymorphs was solved and refined from single crystal X-ray data in a simultaneous refinement. The structures consist of rods of composition Sb₃O₄ separated by isolated iodine ions. The two phases differ only in the next nearest neighbour arrangement. The orthorhombic α-phase crystallizes in space group Pbn2₁, and the monoclinic β-phase in space group P2₁/n.     

Verbindungen im System CsN3?Sr(N3)2?H2O

Compounds in the System CsN₃? Sr(N₃)₂? H₂O Three new compounds between cesium azide and strontium azide have been crystalized from aqueous solutions at room temperature. The lattice parameters wee investigated by means of x-ray single crystal techniques, the indexed powder patterns are listed. CsSr(N₃)₃ crystalizes monoclinic: a = 1 589, b = 1 015, c = 904 pm, β = 90.47°, N = 8, space group P2₁/c. Cs₂Sr(N₃)₄ crystallizes orthorhombic: a = 1 263, b = 1 454, c = 1 183 pm, N = 8, space group Cmca. Cs₂Sr(N₃)₄ · 4 H₂O crystalizes orthorhombic: a = 2 061, b = 1 114, c = 637 pm, N = 4, space group Ccca     

Rare earth substituted fluoride-phosphate apatites

Compositions with the general formula Ln_xM_10?2xNa_x(PO₄)₆F₂ (Ln = La, Pi, Nd, Sm, Eu, Dy, Er, Lu, andY;M = Ca, Sr, and Ba) have been prepared and studied by X-ray diffraction methods. The hexagonal apatite like structure was indicated by the powder patterns of all the compounds (with Ba compounds only when Ln = La through Sm). Single crystal precession data reveal that the crystal lattice of all the compositions in the Ca and Sr system have space group P6₃/m, the Ln₂Ba₆Na₂(PO₄)₆F₂ compounds crystallize in space group P6 and the Ln₃Ba₄Na₃(PO₄)₆F₂ compounds in the trigonal space group P3. Order and disorder mechanisms of the substitution and its dependence on size and polarization effects are discussed.