The structure of the Ba5R8Zn4O21 series (R=lanthanides) was investigated using X-ray Rietveld refinements. The compounds were successfully prepared for R=Eu, Gd, Dy, Ho, Er, Tm, and Yb. Ba5R8Zn4O21 crystallizes in the tetragonal space group I4/m; for R=Yb to Eu, a ranges from 13.635 02(5) to 13.960 62(9) Å, c from 5.658 46(3) to 5.784 83(5) Å, and V from 1051.987(8) to 1127.459(14) Å3. The Zn2+ ions adopt a fivefold distorted square pyramidal coordination. The seven-coordinate R3+ reside in monocapped trigonal prisms. These prisms share edges, and form layers stacked along the c axis. There are two types of BaO polyhedra: bicapped square prisms (BaO10), and irregular BaO10 polyhedra. For larger R, Ba5R8Zn4O21 was not stable, and tetragonal BaR2ZnO5(La, Nd) and orthorhombic BaR2ZnO5(Sm) phases were observed instead.

Powder X-ray diffraction (XRD) data were collected for a new phase of SrGd2O4. Analysis using the Rietveld method was carried out and it was found that the sample crystallizes in the orthorhombic symmetry with CaFe2O4 related structure. The lattice parameters are found to be a=12.0521(2) Å, b=10.1327(2) Å, c=3.4757(4) Å and Z=4. For X-ray data RF=4.9%, RB=7.6%, RP=8.1% and χ2=1.51. The structure can be described as an assembly of bioctahedron [Gd2O10] which are linked together by O2− anions and of dodecahedron of SrO8.

Divalent metal ions are crucial as cofactors for a variety of intracellular enzymatic activities. Mg2+, as an example, mediates binding of deoxyribonucleoside 5′-triphosphates followed by their hydrolysis in the active site of DNA polymerase. It is difficult to study the binding of Mg2+ to an active site because Mg2+ is spectroscopically silent and Mg2+ binds with low affinity to the active site of an enzyme. Therefore, we substituted Mg2+ with Mn2+:Mn2+ that is not only visible spectroscopically but also provides full activity of the DNA polymerase of bacteriophage T7. In order to demonstrate that the majority of Mn2+ is bound to the enzyme, we have applied site-directed titration analysis of T7 DNA polymerase using X-ray near edge spectroscopy. Here we show how X-ray near edge spectroscopy can be used to distinguish between signal originating from Mn2+ that is free in solution and Mn2+ bound to the active site of T7 DNA polymerase. This method can be applied to other enzymes that use divalent metal ions as a cofactor.

The crystal structure of La0.67Ca0.33Mn0.80Cu0.20O3 (LCMCO) compound was determined from laboratory X-ray powder diffraction data and refined by the Rietveld method. LCMCO is isostructural with La0.67Ca0.33MnO3 (LCMO). The crystal data are: La0.64Ca0.36Mn0.82Cu0.18O3.01, Mr=843.80, orthorhombic system, space group Pnma, a=5.4364(1) Å, b=7.6725(2) Å, c=5.4452(1) Å, V=227.124(8)Å3, Z=4, Dx=6.168 g∕cm3. In comparing with the Cu-free compound, subtle structural changes such as bond lengths and bond angles found in the Cu-doped compound may be responsible for the larger effects on the transport and magnetic properties when Cu partially substitutes for Mn in CMCO.

The synthesis and X-ray powder diffraction data for the long-known CaSiF6 and CaSiF6·2H2O species are reported. Their crystal structures have been determined from laboratory powder diffraction data by simulated annealing and full-profile Rietveld refinement methods. CaSiF6·2H2O was found to crystallize in the monoclinic P21/n space group with unit-cell parameters: a = 10.48107(9), b = 9.18272(7), c = 5.72973(5) Å, β = 98.9560(6)°, V = 544.733(8) Å3, and Z = 4. The crystal structure of CaSiF6·2H2O, eventually found to be isomorphous with SrSiF6·2H2O (but not with the Mg analogue—a hexahydrate phase), contains centrosymmetric [Ca(μ-H2O)2Ca]4+ dimers, interconnected by hexafluorosilicate anions, in a dense 3D framework. The crystal structure is completed by a further water molecule, terminally bound to the Ca2+ ion, which, consequently, attains a F5O3 octacoordination. Thermodiffractometric measurements allowed the determination of the linear and volumetric thermal expansion coefficients of CaSiF6·2H2O, which showed a minor contraction, along a, on heating. CaSiF6 is trigonal, space group R-3, a = 5.3497(3), c = 13.5831(11) Å, V = 336.66(5) Å3, and Z = 3, and isomorphous with several other species of MIIAIVF6 or MIAVF6 formulation, among which several silicates, germanates, and stannates.

The current JCPDS powder pattern for the racemic compound fenoprofen calcium dihydrate (card No. 44-1790) is unindexed. Previously we reported the single crystal data, determined at −100 °C, for this material (Zhu et al., 2001). Using 2θ values obtained from a powder pattern spiked with internal standards, we indexed the room temperature powder pattern. The resulting unit cell values for the monoclinic P21/n cell are a=19.018 Å, b=7.738 Å, c=19.472 Å, β=91.66°.

This paper outlines some features of diffraction instrumental monitoring (DIM), a method which can prove helpful to evaluate systematic effects from diffraction measurements and facilitate the comparison of results. The work provides some consideration of the significance of the information contained in diffraction patterns and the ability of DIM methods to yield the effective values of instrumental parameters obtained under working conditions.

X-ray power diffraction data for CrFe3NiSn5 are reported. Indexing the XRD power pattern and Rietveld refinement shows that the compound crystallizes in the hexagonal crystal system, space group P6mm (No. 183) with lattice parameters a=5.3168(1) Å, c=4.4261(1) Å, z=0.6 and Dcalc=8.011 g cm−3. The crystal structure of CrFe3NiSn5 is of the CoSn structure type with Fe, Cr and Ni disordered in the Co position.

Methods of chemical preparation and crystallographic data are reported for two new condensed phosphates: a hydrated cyclotriphosphate with a formula MnNa4(P3O9)2 4H2O and its anhydrous form MnNa4(P3O9)2. MnNa4(P3O9)2 4H2O is monoclinic P21/a with the following unit-cell dimensions: a=8.536(2) Å, b=14.309(3) Å, c=8.508(2) Å, β=96.452(2)°, and Z=2. MnNa4(P3O9)2 is monoclinic C2/c with the following unit-cell dimensions: a=13.198(2) Å, b=8.241(1) Å, c=14.228(2) Å, β=95.045(1)°, and Z=4.

The ferroelectric liquid crystal material [4-[(4-methyloxyfenyl) carbonyloxyl] bifenyl-4′-yl]-(S)-2-methylbutoxypropionate containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit and two chiral carbons has been investigated by X-ray powder diffraction analysis at the 28 °C–105 °C temperature range. On cooling through the SmC temperature range, the layer spacing decreases from 28.3 to 27.7 Å with a small variation of average intermolecular distances. Lattice parameters of tetragonal and monoclinic crystalline phases occurring at lower temperatures have been determined.

A poster session was held during the Annual Spring Meeting of the International Centre for Diffraction Data on 20 March 2002. Abstracts of the posters are reproduced in the following. The underlined authors can be contacted for more information.

Data for the standard material NBS SRM 674, TiO2, were collected on two diffractometers: a) a Philips PW 1050/37 standard diffractometer of the Bragg-Brentano type equipped with a post diffraction curved Ge monochromator, b) a Stoe Stadi P diffractometer of transmission type equipped with a curved incident beam Ge monochromator. Both monochromators were set to select pure CuKα1 radiation. The reflection type instrument gives a much larger peak to background ratio than the transmission instrument, for which the background is much higher than with the reflection instrument. Rietveld refinements were carried out on both data sets with the programs DBWS-9807 and general structure analysis system (GSAS). The structural parameter of the oxygen atom of rutile depends neither on data set nor program, whereas, e.g., thermal displacement parameters seem to depend on both data set and program.

The atomic displacement parameters of individual ions in SrO have been determined from the Rietveld analysis of high-resolution powder neutron diffraction data. As the neutron velocity is smaller than the sound velocity in SrO, the intensity data was not corrected for the effect of thermal diffuse scattering. The room temperature value of overall isotropic thermal displacement parameters was B=0.57(2) Å2; which corresponds to Debye temperature, Θ of 242(4) K. The results are compared with experimental and theoretical estimates.

Silver sulfide, Ag2S, is most commonly known as the tarnish that forms on silver surfaces due to the exposure of silver to hydrogen sulfide. The mineral acanthite is a monoclinic crystalline form of Ag2S that is stable to 176°C. Upon heating above 176°C, there is a phase conversion to a body-centered cubic (bcc) form referred to as argentite. Further heating above 586°C results in conversion of the bcc phase to a face-centered cubic (fcc) phase polymorph. Both high-temperature cubic phases are solid-state silver ion conductors. In situ high-temperature X-ray diffraction was used to better understand the polymorphs of Ag2S on heating. The existing powder diffraction file (PDF) entries for the high-temperature fcc polymorph are of questionable reliability, prompting a full Rietveld structure refinement of the bcc and fcc polymorphs. Rietveld analysis was useful to show that the silver atoms are largely disordered and can only be described by unreasonably large isotropic displacement parameters or split site models.

Methods of chemical preparation and crystallographic data are reported for two new condensed phosphates: a polyphosphate of nickel and cesium, NiCs4(PO3)6, and a cyclotriphosphate of nickel and potassium, NiK4(P3O9)2. NiCs4(PO3)6 is rhombohedral with the following unit-cell dimensions: a=b=11.602(1) Å, c=9.078(1) Å, space group P−31c, V=1058.24(1) Å3, and Z=2. NiK4(P3O9)2 is triclinic with the following unit-cell dimensions: a=6.143(8) Å, b=6.80(1) Å, c=12.80(3) Å, α=102.8(3)°, β=89.7(2)°, γ=66.03(7)°, space group P−1, V=473.56(3) Å3, and Z=1.