Volume 220, Issue 2-3

Single crystals of the new compound Tb 3 Zn 3.6(1) Al 7.4(1) were obtained from Al and Zn-rich ternary solutions. The title compound crystallizes in the orthorhombic La 3 Al 11 structure type (space group Immm (No. 71), Z = 2; a = 4.2334(1) Å, b = 9.9725(3) Å, c = 12.4659(1) Å). The inverse susceptibility above ca. 50 K shows Curie-Weiss behavior, and a metamagnetic transition is apparent in the T = 2 K field-dependent magnetization around H c ∼ 20 kG. The resistivity increases with temperature in a roughly linear fashion, indicating the metallic character of this material. TB-LMTO-ASA electronic structure calculations indicate that this new intermetallic phase has all bonding states optimized in the [Zn 4–x Al 7+x ] network, which classifies this compound among the so-called “polar intermetallics”. The calculations also provide a rationalization of the nonrandom ordering of Zn and Al atoms, which can be attributed to optimizing (Zn, Al)—(Zn, Al) orbital interactions.

The title compound with the trivial name γ -AgMg 4 is obtained by melting the elements in weld-sealed tantalum ampoules and subsequent annealing. The alloys were characterized by chemical, metallographic, thermal and X-ray powder analyses. γ -AgMg 4 is formed by a peritectoid reaction at 472(2) °C from ɛ ′-Ag 17 Mg 54 and δ -(Mg). The exact composition corresponds to the formulas AgMg 4.08 or Ag 9 Mg 36.7 with 80.3(1) at-% Mg concentration. The title compound is a complex metallic alloy phase due to the large number of atoms and intrinsic structural disorder. γ -AgMg 4 crystallizes hexagonal in the space group P 6 3 / m with a = 12.4852(8) Å and c = 14.4117(9) Å in a unique structure type without a perceptible homogeneity range. The crystal structure has been studied including disorder phenomena by means of Rietveld refinements of X-ray and neutron powder diffraction data and X-ray single crystal structure analyses. The crystal structure is a hitherto unknown I 3 cluster phase, i.e., an intermetallic compound with building blocks of three vertex connected icosahedra as the fundamental structural units joined via a small number of connection types (here B- and L-type). Channels along [001] reveal distinct structural disorder described as a packing of approximately 1.9 icosahedra, 1.3 tricapped trigonal prisms and 0.4 Frank-Kasper Z15 polyhedra per unit cell. The findings support the usefulness of the I 3 cluster concept as a construction kit concerning not only simple subunits but also more complex “patches” with inherent structural disorder.

Single crystals of the new intermetallic compound La 16 Al 13 were obtained by thermal treatment of (La 3 O)Al in sealed Ta ampoules at 973 K, powder material for physical properties measurements from melt beads of appropriate composition at 773 K, well below the peritectic temperature of 978 K of the decomposition into LaAl and liquid. La 16 Al 13 crystallizes hexagonal (space group P -62 m , a = 918.3(2) pm, c = 1123.8(3) pm, R gt ( F ) = 0.0293, R all ( F ) = 0.0299, wR ( F 2 ) = 0.0621) with one formula unit per unit cell. The crystal structure can be described as built from layers of face-sharing Edshammar polyhedra (AlLa 2 La 9/2 ) 2 alternating with layers of barrelane-like Al 11 cages linked by La. La 16 Al 13 is a Pauli-paramagnet with metallic electrical resistivity. Electron localization function calculation reveals covalent interactions within the Al 11 cages. The resulting large number of the ‘free’ charge carriers explains the metal-like transport and magnetic properties in good agreement with the experiments and electronic band-structure calculation.

Structural properties of the ternary intermetallic compound CeAuGe were investigated at hydrostatic pressures up to 15 GPa with high-resolution angle dispersive X-ray powder diffraction using synchrotron radiation and the diamond anvil cell technique. At 8.7(7) GPa a first order phase transition is observed from a hexagonal NdPtSb-type arrangement into an orthorhombic high-pressure modification with a TiNiSi-type crystal structure. The transformation is associated with a 3% shortening of the lattice parameter perpendicular to the puckered layers [AuGe] n and an elongation of one of the lattice parameters within the plane of the layers. The changes of interatomic distances are more pronounced than the metrical alterations and indicate that a transition from layer-type poly anions into a 3D network [AuGe] n is associated with the structural transformation.

An incommensurately modulated structure of CeSi 1.82 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 I 2/ b ( αβ 0)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.

The two new oxoferrates(III) Cs 6 [Fe 2 O 6 ] and Rb 4 [Fe 2 O 5 ] were synthesized at temperatures of 500 and 600 °C via reaction of Fe 2 O 3 with the elemental alkali metals (A) and their hyperoxides AO 2 in the form of dark-red crystals. Their crystal structures have both been determined by single crystal X-ray diffraction. The structure of Cs 6 [Fe 2 O 6 ] (monoclinic, P 2 1 / c , a = 724.6(2), b = 1212.1(5), c = 767.6(3) pm, β = 105.03(4)°, Z = 2, R 1 = 0.0272, K 6 [Mn 2 O 6 ] structure type) contains isolated bi nuclear anions [O 2 FeO 2 FeO 2 ] 6- composed of two edge sharing FeO 4 tetrahedra, which are also known from the potassium and rubidium compounds A 6 [Fe 2 O 6 ] that crystallize in the klassengleiche super group C 2/ m . Comparable building blocks are connected via common O vertices to form chains 1 ∞ [O 1/2 OFeO 2 FeOO 1/2 ] 4– in the rubidium ferrate(III) Rb 4 [Fe 2 O 5 ] (monoclinic, C 2/ c , a = 711.43(14), b = 1750.0(5), c = 725.3(2) pm, β = 104.72(2)°, Z = 4, R 1 = 0.0611). As a consequence of the edge sharing of FeO 4 tetrahedra, both compounds show short Fe—Fe distances of 273.3(2) pm in Cs 6 [Fe 2 O 6 ] and 265.6(3) pm in Rb 4 [Fe 2 O 5 ] respectively. Based on similarities in the packing of the (Fe III /A I ) cations, a structural relationship between the two compounds can be derived. The influence of the different counterions on the structure of the oxoferrate units in the phases of general composition A 6 [Fe 2 O 6 ] and A 4 [Fe 2 O 5 ] is discussed.

Alkali metal decahydro- closo -decaborates M 2 [B 10 H 10 ] (M = Na, Rb, Cs) were synthesised by ion-exchange and characterised via infrared and 11 B-NMR spectroscopy. The crystal structures of Na 2 [B 10 H 10 ], K 2 [B 10 H 10 ], and Rb 2 [B 10 H 10 ] were determined from X-ray powder diffraction data using real-space techniques. The compounds crystallise in the monoclinic space group P 2 1 / n (no. 14) with the lattice constants: Na 2 [B 10 H 10 ]: a = 1028.28(6) pm, b = 1302.18(5) pm, c = 667.34(3) pm, β = 93.754(3)°; K 2 [B 10 H 10 ]: a = 1285.54(8) pm, b = 1117.84(7) pm, c = 682.27(4) pm, β = 93.357(3)°; Rb 2 [B 10 H 10 ]: a = 1320.04(7) pm, b = 1136.88(6) pm, c = 704.23(4) pm, β = 94.158(3)°. The hydroborate anions are arranged almost hexa gonally with alkali metal cat ions in the tetrahedral interstices.

The reactions of BiCl 3 with AlCl 3 and of BiBr 3 with AlBr 3 yield [Bi 2 Cl 4 ][AlCl 4 ] 2 1 and [Bi 2 Br 4 ][AlBr 4 ] 2 2 in almost quantitative yield. The reactions were performed in closed, evacuated glass ampoules at temperatures of 240 °C and 200 °C, respectively. The colorless and yellow crystals are sensitive towards hydrolysis by moist air. 1 crystallizes in the monocline space group P 2 1 / c ( a = 7.7322(2) Å, b = 11.9565(3) Å, c = 10.3535(3) Å, β = 95.090(2)°, Z = 2), 2 crystallizes in the triclinic space group P -1 ( a = 7.693(2) Å, b = 7.706(2) Å, c = 9.739(2) Å, α = 104.19(2)°, β = 102.65(2)°, γ = 99.46(2)°, Z = 1). Both structures are made up of [Bi 2 X 4 ] cations and [AlX 4 ] – anions. The centrosymmetric cations consist of four membered Bi 2 X 2 rings with an additional halogen atom attached to each Bi atom in a trans arrangement. The tetrahalogeno aluminate ions are almost regular tetrahedral. Although both compounds contain isomorphous ions, the structures of 1 and 2 are not isotypic. The different packing can be understood by abstracting both structures to simple AB 2 types. 1 adopts the PtHg 2 structure type with eightfold coordination of the cations whereas 2 adopts the MoSi 2 structure with tenfold coordination.

Single crystals of CuPb 3 Br 7 were solvothermally synthesized starting with CuBr and PbBr 2 in diethylene glycol at a temperature of 453 K. Two reversible phase transitions were observed with the DSC method at temperatures of 156 K and 433 K. The crystal structures of the low and medium temperature modifications were determined with single crystal X-ray diffraction method. Both modifications can be derived from the Sr 7 Pt 3 type structure and can be differentiated by minor atomic displacements and partial occupation of the additional copper positions.

The low-temperature oxidation of the rare earth metals europium and ytterbium with the 1-N amines pyrrole and carbazole in liquid ammonia gave the pyrrolate 1 ∞ [Eu 2 ( Pyr ) 4 ( Pyr H) 2 (NH 3 )] · Pyr H (1) ( Pyr – = C 4 H 4 N – , pyrrolate anion; Pyr H = C 4 H 4 NH, pyrrole) and the carbazolate [Yb 2 ( Cbz ) 4 (NH 2 ) 2 (NH 3 ) 4 ] · 3 Cbz H (2) ( Cbz – = C 12 H 8 N – , carbazolate; Cbz H = C 12 H 8 NH), respectively. Though both compounds are ammine complexes, the course through the redox potentials E Ln(II/III) as well as the growing steric demand of the ligand result in various differences in the properties of the products. 1 shows a 1-dimensional structure of pyrrolate, pyrrole groups and one equivalent of ammonia coordinating and bridging divalent europium centers. This includes η 5 – π -interactions between the metal centers and pyrrolate and pyrrole rings. The resulting polymer shows a rather high thermal stability and melts at 445 °C prior to decomposition under release of ammonia at 475 °C. Contrary to this, 2 contains dimeric units around trivalent ytterbium consisting of carbazolate, ammonia and NH – 2 amide groups. No π -interactions are observed. Instead ammonolysis of liquid ammonia results in formation of an amide that contains two different amide groups. The thermal stability of 2 is lower than of 1 . The building units of complex 2 decompose at 310 °C without melting. Both compounds were investigated by low-temperature single crystal X-ray analysis, Mid IR, Far IR and Raman spectroscopy as well as simultaneous DTA/TG.

ZrOI 2 · 8 H 2 O was synthesized from ZrI 4 and concentrated aqueous HI leading to colourless crystals. Single X-ray diffraction data gave a monoclinic cell with a = 8.392(5) Å, b = 37.497(5) Å, c = 16.217(5) Å and β = 102.76(6) Å in P 2 1 / c . The zirconyl cation is tetrameric, the iodide anions exhibit no contacts to the zirconium atoms but are linked to the tetrameric cations by weak hydrogen bridge bonds.

A synthetic Cs-fluorohectorite was intercalated with Tetramethylammonium-cations (TMA + ). Under appropriate reaction conditions, a complete cation exchange is feasible while preserving the phase relationship between adjacent silicate layers. Starting from a three-dimensionally (3D) ordered [1] and homogeneously charged [2], synthetic Cs-hectorite it is possible to synthesize single crystals of a 3D ordered intercalation compound (TMA-hectorite). Single crystal structure refinement (TMA 0.5 inter Mg 2.5 Li 0.5 oct Si 4 tet O 10 F 2 , monoclinic, C 2/ m , a = 5.2735(11) Å, b = 9.1165(14) Å, c = 13.5609(35) Å, β = 97.693(3)°, V = 646.1(2) Å 3 , Z = 2) conclusively reveals the arrangement of the TMA-cations in the interlayer space. The results are compared with an earlier structure refinement of an analogous TMA-intercalated natural vermiculite [3] and the results of a computer simulation carried out on TMA-vermiculite [4].

Single crystals of Gd 2 (Cl 3 CCOO) 6 (bipy) 2 × (H 2 O) 2 · 4 bipy, Pr(Cl 3 CCOO) 3 (bipy) 2 , Nd(Cl 3 CCOO) 3 × (bipy) 2 and Er(Cl 3 CCOO) 3 (bipy) 2 (H 2 O) have been obtained by reaction of the corresponding trichloroacetate salts with 2,2′-bipyridyl (bipy) in a water/ethanol (1:1) solution. Gd 2 (Cl 3 CCOO) 6 (bipy) 2 (H 2 O) 2 · 4 bipy crystallizes in the monoclinic space group P 2 1 / c (no. 14, Z = 4, a = 1642.40(9) pm, b = 1227.36(10) pm, c = 2303.48(14) pm, β = 107.043(7)°). The Gd 3+ ions are bridged to dimers by carboxylate groups and are surrounded by six oxygen and two nitrogen atoms. One 2,2′-bipyridyl molecule is coordinated to Gd 3+ , the two other ones are non-coordinated. The monomeric compounds Ln(Cl 3 CCOO) 3 (bipy) 2 (Ln = Pr, Nd) are isotypic with each other and crystallize in the triclinic space group P -1 (no. 2, Z = 2, Pr: a = 989.83(8) pm, b = 1032.22(8) pm, c = 1791.56(13) pm, α = 99.312(9)°, β = 102.036(9)°, γ = 99.166(9)°; Nd: a = 990.09(7) pm, b = 1030.74(8) pm, c = 1788.70(13) pm, α = 99.393(9)°, β = 102.064(8)°, γ = 99.242(9)°). The Ln 3+ atom is surrounded by six oxygen and four nitrogen atoms. A chelating coordination by the carboxylate groups is observed. There are two 2,2′-bipyridyl molecules coordinated to Ln 3+ . The compound Er(Cl 3 CCOO) 3 (bipy) 2 (H 2 O) crystallizes in the triclinic space group P -1 (no. 2, Z = 2, a = 1060.65(9) pm, b = 1273.35(11) pm, c = 1402.49(11) pm, α = 105.484(10)°, β = 104.504(9)°, γ = 93.712(10)°). The Er 3+ ion is coordinated by four oxygen and four nitrogen atoms. There are two 2,2′-bipyridyl molecules attached to Er 3+ .

[Ba 2 (C 2 H 6 O 2 ) 4 ][Ge 2 (C 2 H 4 O 2 ) 6 ] · 2.5 C 2 H 6 O 2 ( 3a ) is isolated from the reaction of GeO 2 · aq with Ba(OH) 2 · 8 H 2 O in glycol (1,2-ethanediol). 3a crystallizes in the space group P -1 with a = 10.324(2) Å, b = 13.932(3) Å, c = 15.800(3) Å, α = 102.86(2)°, β = 91.33°, γ = 109,47° and V = 2077.2(7) Å 3 . With increasing temperature 3a looses glycol and forms step by step [Ba(C 2 H 6 O 2 ) 2 ][Ge(C 2 H 4 O 2 ) 3 ] ( 3b ), Ba[Ge(C 2 H 4 O 2 ) 3 ] ( 3c ) and finally hexagonal BaGeO 3 ( 4 ).

{[Li(NH 3 ) 4 ] 2 [18-crown-6]}[Li(NH 3 ) 4 ] 2 (Sn 3 ph 6 ) 2 · 4 NH 3 was prepared by reacting diphenyltin dichloride with lithium and 18-crown-6 in liquid ammonia. The crystal structure was obtained from low temperature single crystal X-ray data ( P 2 1 / a , Z = 2, a = 18.483(5) Å, b = 13.240(2) Å, c = 22.919(5) Å; β = 103.65(3)°). The structure is built from previously unknown catena -hexaphenyltristannandiide anions, Sn 3 ph 6 , isolated tetraamminelithium complexes, and novel {[Li(NH 3 ) 4 ] 2 [18-crown-6]} 2+ cations. In the latter divalent cation, two tetraamminelithium complexes coordinate to both sides of the crown ether via hydrogen bonds.

The thermal decomposition of Nd(NH 2 SO 3 ) 3 · 2 H 2 O in a closed tube leads to violet single crystals of Nd(NH 2 SO 3 )(SO 4 ) · 1.5 H 2 O. The compound crystallizes with the space group P 1 ( Z = 2, a = 689.2, b = 691.4, c = 962.0 pm, α = 109.64, β = 97.00, γ = 109.62°). The triclinic unit cell can be transformed into the respective bodycentered setting I 1 ( Z = 2, a = 977.9, b = 795.6, c = 1113.0 pm, α = 90.69, β = 115.06, γ = 88.98°) leading to a nearly monoclinic unit cell for the compound. In the crystal structure of Nd(NH 2 SO 3 )(SO 4 ) · 1.5 H 2 O two Nd 3+ ions are present. Nd(1) 3+ is coordinated by four NH 2 SO 3 – and two SO 4 2– ions, and one H 2 O molecule. Owing to the chelating attack of the sulfate groups, the CN is nine. Nd(2) 3+ is surrounded by four monodentate SO 4 2– and two NH 2 SO 3 – groups. Two H 2 O ligands fill up the coordination sphere and lead to a CN of eight. The linkage of the polyhedra leads to a three-dimensional network.

For the growth of group-III nitride thin films as well as GaN and AlN bulk phases precursors are widely used. Here, we introduce bulk phases of pure GaN, InN and solid solutions of In x Ga 1–x N synthesized by pyrolysis of molecular precursors in ammonia atmosphere. The dimeric [M(NMe 2 ) 3 ] 2 (M = Al, Ga) is an oftentimes discussed precursor for conversion into group-III nitrides, while the other here presented gallium and indium amide derivatives have not been reported as appropriate precursors in literature so far. The given molecular structure of the precursors lead to a homogeneous distribution of Gallium and Indium on the cation positions in the solid solutions. GaN and InN and their solid solutions crystallizing in the wurtzite structure type follow Vegard’s law and therefore the lattice constant a 0 gives a hint about the degree of cations substitution in the structure. For the investigations of the synthesized bulk phases XRD, SEM and TEM coupled with EDX were used.

A total of 23 solid, mineral-like samples from calcified aortic valves of human origin have been investigated by means of classic analytical techniques (atomic absorption spectroscopy) and powder X-ray diffraction methods (Rietveld approach). The calcification goes back to hexagonal Ca-deficient hydroxyapatite, and there is a large variance in absolute hydroxyapatite contents as well as in crystalline qualities. The source of the calcium deficiency has been traced back to the 4 f calcium site of the crystal structure in P 63/ m , and the calcium loss is compensated by hydroxy group deficiencies. Despite no correlation between analytically and diffractionally determined calcium contents, the crystallinities of the samples and the sharpnesses of their Bragg peaks seem to be related with the sub-occupancy of the 4 f calcium site.

The lanthanoid chalcogenide ortho -oxosilicates M 4.667 Ch[SiO 4 ] 3 (M = Nd, Sm; Ch = O, S) with apatite -type crystal structure have been synthesized by the reaction of either M 2 O 3 and SiO 2 or M 2 O 3 , M, S and SiO 2 using CsCl as flux in evacuated silica tubes at 850 °C for 7 d . The title compounds crystallize hexagonally in the space group P 6 3 /m with two formula units per unit cell. Their crystal structure contains two crystallographically independent lanthanoid cations, of which (M1) is surrounded by nine O ligands in the shape of a tricapped trigonal prism. Additionally, this site is only occupied by 81–84% to assure that the composition is electroneutral. The (M2) cations have an environment of seven O anions in the case of M 4.667 O[SiO 4 ] 3 , which form a pentagonal bipyramid. Considering M 4.667 S[SiO 4 ] 3 this polyhedron changes, when one of the apical oxide particles is substituted by two sulfide ligands which then form a “two-legged” pentagonal bipyramid. Both the non -silicon bonded oxygen in the oxide derivative and the sulfur in the sulfide homologue are situated in a channel along [001]. While oxygen prefers a trigonal planar cationic coordination at the Wyckoff position 2 a (CN = 3), the sulfur represents the centre of a trigonal antiprism at the Wyckoff position 2 b (CN = 6).

The crystal structure of inverse spinel-type (space group Fd -3 m , Z = 8), quaternary lithium chloride Li 1.8 Na 0.2 MgCl 4 has been determined by neutron powder diffraction methods ( a = 1044.16(7) pm, 114 reflections, R exp = 5.23%). The sodium ions are solely placed at the octahedral 16 d site together with the Mg and a part of the Li + ions. These results are in agreement with analogous studies on the manganese compound (Lutz et al., 1989) but being in contradiction with the results of 6 Li and 7 Li MAS NMR experiments (Nagel et al., 2002). The reason of this discrepancy is discussed.

The sublimation of 2-amino-4,6-dichloro-1,3,5-triazine yielded well developed needle-shaped crystals whose X-ray-powder pattern did not match with that of the known orthorhombic compound with the space group P 2 1 2 1 2 1 [1]. The investigation of a needle-shaped single crystal revealed a new monoclinic modification, which crystallizes in the space group P 2 1 / c . At T = 220 K the following lattice parameters were refined: a = 8.403(1) Å, b = 12.152(1) Å, c = 13.898(2) Å and β = 123.01(1)°. The unit cell volume amounts to 1190(1) Å 3 for 8 formula units.

In-situ neutron powder diffraction investiägations of the oxygen super-ionic conductors La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 2.85 and La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 2.80 were performed at 1460 K with and without an applied electric field ( U = 3 V DC) resulting in lasting ionic currents of 180–270 mA. At this temperature both samples adopt the cubic perovskite structure ( Pm -3 m ). Field-induced structural changes are evidenced by anharmonic terms in the Debye-Waller factors of oxygen only for the first sample. The corresponding probability density function maps indicate curved diffusion pathways around the Ga atoms shifted further into the direction of an octahedral void with applied field. In addition, double maxima appear in the direction of the Ga—O bond which are more prominent in the second sample. A tentative explanation of the observed phenomena is given in terms of long range ordering of the corresponding potential minima and residual short range order clusters persisting at high temperatures.

We study the coarsening of two-dimensional crystalline islands on the (001) face of GaAs, InAs and GaSb after deposition at typical growth conditions in molecular beam epitaxy. The time-resolved island/pit size distributions are measured in situ using synchrotron X-ray diffraction and are analyzed together with the diffraction intensity oscillations during deposition. Whereas the deposition kinetics is similar for the three materials, they strongly differ in the coarsening. During coarsening, the mean correlation length grows proportional to t n . GaAs shows coarsening exponents around n = 1 and an exponential island size distribution, in clear contrast to the behavior of InAs and GaSb, where we find coarsening closer to the expected Ostwald ripening behavior ( n between 1/3 and 1/2) on InAs and extremely slow kinetics on GaSb.

The real stucture of a new crystalline high temperature phase, metastable at room temperature, in the system sodium – bismuth – oxygen, β -Na 3 BiO 4 , was determinated using high resolution X-ray powder diffraction, pair distribution function analysis, and high resolution transmission electron microscopy. β -Na 3 BiO 4 was synthesized by anodic oxidation of bismuth(III)-oxide in a sodium hydroxide – lithium hydroxide melt. The average crystal structure of β -Na 3 BiO 4 at ambient conditions ( R 3 m, a = 3.32141(9) Å, c = 16.4852(5) Å) is structurally related to α -NaFeO 2 with metal layers almost statistically occupied in a Na:Bi ratio of 3:1. Analysis of the long-range order on the bulk material by Rietveld refinement led to approximately Na:Bi ratios of 2:1 and 4:1, in consecutive metal layers, while a detailed analysis of the local order by means of the pair distribution function revealed the existence of almost pure sodium layers and mixed 1:1 – sodium:bismuth layers. Complementary studies on single crystallites using high resolution transmission electron miscroscopy exhibited a complex domain structure with short-range ordered, partially ordered, and long-range ordered domains.

The high-pressure behaviour of the oxonitridosilicate chlorides Ce 4 [Si 4 O 3+x N 7–x ]Cl 1–x O x , x = 0.12 and 0.18, is investigated by in situ powder synchrotron X-ray diffraction. Pressures up to 28 GPa are generated using the diamond-anvil cell technique. A reversible phase transition of first order occurs at pressures between 8 and 10 GPa. Within this pressure range the high- and the low-pressure phases are observed concomitantly. At the phase transition the unit cell volume is reduced by about 5%, and the cubic symmetry (space group P 2 1 3) is reduced to orthorhombic (space group P 2 1 2 1 2 1 ) following a translationengleiche group-subgroup relationship of index 3. A fit of a third-order Birch-Murnaghan equation of state to the p – V data results in a bulk modulus B 0 = 124(5) GPa with its pressure derivative B ′ = 5(1) at V 0 = 1134.3(4) Å 3 for the low-pressure phase and in B 0 = 153(10) GPa with B ′ = 3.0(6) at V 0 = 1071(3) Å 3 for the high-pressure phase. The orthorhombic phase shows an anisotropic axial compression with the a axis (which is the shortest axis) being more compressible ( k(a) = 0.0143(4) 1/GPa) than the b and c axes ( k(b) = 0.0045(2), k(c) = 0.0058(2) 1/GPa). The experimental results confirm an earlier prediction of the pressure-induced instability of isotypic Ce 4 [Si 4 O 4 N 6 ]O, and also show that the bulk modulus was predicted reasonably well.

Single crystals of Ba 2 (ADC)(NO 3 ) 2 · 4 H 2 O ( 1 ), Ba 7 (ADC) 6 (NO 3 ) 2 · 14 H 2 O ( 2 ), and Ba 3 (ADC) 2 Cl(NO 3 ) × 5 H 2 O ( 3 ) were prepared by crystallisation at the phase boundary of a two phase system (ADC = C 2 (COO) 2 ). They crystallize in noncentrosymmetric space groups ( 1 : C 222 1 , Z = 4; 2 : I 2, Z = 2; 3 : P 22 1 2, Z = 2). For 1 a SHG signal of approx. 0.29 KDP (1 KDP = SHG of KH 2 PO 4 ) was determined. All hitherto known compounds of the almost linear dianion of acetylenedicarboxylic acid crystallize in centrosymmetric space groups, but by inserting trigonal planar nitrate anions into the crystal structure a symmetry breaking seems to occur, which leads to noncentrosymmetric crystal structures. Several examples from the literature show that this observation might be also valid for other compounds.

The crystal structure of γ -P 4 , one of three modifications hitherto reported on white phosphorus, was determined from X-ray powder diffraction data collected at T = 123 K on a Guinier-Simon camera equipped with a cold gas blower and an image plate detector. Crystallographic data at T = 123 K are: space group C 2/ m , a = 9.1709(5) Å, b = 8.3385(5) Å, c = 5.4336(2) Å, and β = 90.311(3)°, V = 415.51(6) Å 3 , Z = 4. The crystal structure of γ -P 4 was solved by the method of simulated annealing. The subsequent Rietveld refinement in the range 12° < 2 θ < 92° employing rigid-body constraints on the P 4 molecule converged at R p = 3.8, wR p = 5.0, and R F 2 = 14.0%. The asymmetric unit of γ -P 4 contains three P atoms; two P atoms in a molecule are related by a mirror plane which bisects the molecule. The centers of gravity of these P 4 molecules show a distorted body-centered cubic arrangement. The four apices of the P 4 tetrahedron point to the largest possible voids formed by neighbor molecules. The difference to the crystal structures of SiF 4 and GeF 4 with an exact bcc arrangement of tetrahedral molecules is discussed as well as, in terms of layer stackings, the similarity of the structures of γ - and β -P 4 .

New phosphorus-rich phosphorus selenides P 14+x Se ( x = 1, 5) were synthesized by reaction of amorphous red phosphorus and SeO 2 . The crystal structures of P 15 Se and P 19 Se were solved from single-crystal X-ray data (space group Pnma (No. 62); P 15 Se: a = 9.963(2) Å, b = 3.231(1) Å, c = 13.412(3) Å; P 19 Se: a = 9.917(2) Å, b = 3.230(1) Å, c = 13.410(3) Å). The structures consist of pentagonal tubes packed collaterally with two-dimensional disorder, which was confirmed by TEM investigations.

Single crystals of the new 8O modification of Ca 2 Ta 2 O 7 were grown by optical floating zone melting and their structure was solved by X-ray diffraction. 8O Ca 2 Ta 2 O 7 crystallizes in space group C 222 1 with a = 7.3690(2) Å, b = 12.7296(3) Å, c = 48.263(1) Å. The structure is related to the weberite structure type and can be described as a stacking of 8 basic building units per unit cell. Each building unit consists of one Ta 3 Ca and one Ca 3 Ta layer with a cubic close packed arrangement. Transmission measurements in the UV-Vis and IR region reveal a high transparency in a wide energy range from 0.2–3.5 eV. Dielectric measurements yield a high ɛ ′ value of 60 at room temperature.

ZnGa 2 S 4 :Eu 2+ shows a light green emission at room as well as at low temperatures. The maximum of the band of the 4f 6 5d 1 → 4f 7 emission is located at about 536 nm (18657 cm –1 ) and depends slightly on the excitation energy. The respective excitation band has a maximum at 470 nm (21277 cm –1 ). These results lead to the assumption that the Eu 2+ ions are substituted at octahedral voids of the host lattice rather than at cationic sites. This is to be expected also because of the different ionic radii of the cations. Further emission and excitation bands are detected at higher energies in ZnGa 2 S 4 :Eu 2+ as well as in undoped ZnGa 2 S 4 which depend strongly on the respective excitation and emission energies and can, thus, be assigned to host lattice bands.

The crystal structures of 12 argyrodite type copper compounds with the general formula Cu (12–) B +n Q 2– 6–y X – y ( B = P, As, Si, Ge; Q = S, Se; X = Cl, Br, I) were refined. The positions of the copper atoms were refined by using a non-harmonic approach. All polymorphic argyrodites were investigated in their cubic high temperature modification crystallizing in spacegroup F -43 m (No. 216). A comprehensible way to describe the complex structures was developed based on a topological description of the rigid anion- and B -cation substructure as an arrangement of Frank-Kasper polyhedra. An analysis of the joint probability density function and of the one particle potentials for the copper atoms was performed to get a detailed insight in the copper distribution in these argyrodites. They can be divided into four types based on their different distribution of copper. This classification corresponds to the physical properties of the argyrodites, especially to their ionic conductivities, which show a significant dependence on the composition.

We report on the preparation and characterization of a niobium containing Keggin type heteropolyoxomolybdate (HPOM), H 4 [PNbMo 11 O 40 ] · 13 H 2 O, with Nb substituting Mo in the Keggin ion. H 4 [PNbMo 11 O 40 ] · 13 H 2 O exhibits a long-range order structure similar to that of H 3 [PMo 12 O 40 ] · 13 H 2 O. The structural evolution of H 4 [PNbMo 11 O 40 ] · 13 2 O was studied under reducing (propene) and partial oxidation reaction conditions (propene and oxygen) by in situ X-ray diffraction and X-ray absorption spectroscopy combined with mass spectrometry and corroborated by thermogravimetric analysis. Following the loss of crystal water in the temperature range from 373 K to 573 K, a partial decomposition and reduction of the molybdenum and the formation of a characteristic cubic HPOM is observed at 573 K, similar to the structural evolution of H 3 [PMo 12 O 40 ] · 13 H 2 O and H 4 [PVMo 11 O 40 ] · 13 H 2 O during treatment in propene. However, in contrast to H 3 [PMo 12 O 40 ] · 13 H 2 O and H 4 [PVMo 11 O 40 ] · 13 H 2 O, the cubic HPOM decomposes rapidly and the MoO 3 formed is subsequently reduced to MoO 2 . Nb centers in the Keggin ion considerably destabilize the HPOM and accelerate the decomposition towards MoO 3 . A similar structural evolution is observed under propene and oxygen. The formation of the cubic HPOM with Mo centers on extra-Keggin framework positions coincides with the onset of catalytic activity. However, at about 673 K the active phase further decomposes to a mixture of MoO 3 and a more stable cubic HPOM resulting in a pronounced decrease of the catalytic activity. Evidently, preparation and structure-activity relationships for Nb containing mixed metal oxide catalysts need to take into account the particular structure directing properties of Nb during thermal activation.

Powder samples of β -Ni(OH) 2 and doped variants of the α -Ni(OH) 2 structure type were prepared by a coprecipitation method. Chemical composition was analysed by ICP. Samples were measured by X-ray powder diffraction (XRD). Single peak profiles were analysed by fitting a splitted Pearson VII funktion to the measured patterns. Peak profile data were collected and a strong anisotropic peak broadening was observed. Structure models of possible stacking orders in β -Ni(OH) 2 and doped α -Ni(OH) 2 were developed. DIFFaX simulations of structure models with statistical stacking orders were carried out. The simulated peak profiles were compared to the measured ones and a fairly good agreement was found. A semiquantitative analysis of the stacking faults in these materials is shown.