Space Group Pmna Research Articles

Lanthanum Indium Oxide from X‐Ray Powder Diffraction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Lanthanum indium oxide from X-ray powder diffraction

LaInO(3), a promising ion conductor for a holistic solid oxide fuel cell, was synthesized by a solid-state reaction method. The structure was refined by the Rietveld method using X-ray powder diffraction data. The structure of LaInO(3) is distorted by the in-phase and antiphase tilting of oxygen octahedra in the a(+)b(-)b(-) system of the InO(6) polyhedra. In the Pmna space group, the In atom lies on an inversion centre and the La atom and one of the O atoms lie on a mirror plane.

57Fe Moessbauer and X-ray Rietveld studies of ferrian prehnite from Kouragahana, Shimane Peninsula, Japan

Fe-bearing prehnite, Ca2Al2-pFepSi3O10(OH)2 (Z=2), from Kouragahana, Shimane Peninsula, Japan, was investigated using 57Fe Mossbauer spectroscopy and X-ray Rietveld method. Iron and aluminum contents of the prehnite are variable, with p ranging from 0.003 to 0.425 (n=97). Fe-poor and Al-rich prehnites generally grow over clusters of Fe-rich prehnite crystals. Intergrowth texture of Fe-poor and Fe-rich crystals is also common in spherical aggregates. The 57Fe Mossbauer spectrum consists of one doublet with isomer shift = 0.360 mm/s, quadrupole splitting = 0.276 mm/s and peak width = 0.310 mm/s. The doublet is assigned to Fe3+ in the octahedral site. X-ray Rietveld refinement was carried out using two structural models of space groups Pmna and Pma2, Results of the refinement are characterized by R-weighted pattern (Rwp) = 9.30 %, ‘Goodness-of-fit’ indicator (S) = 1.276 and Durbin-Watson statistic d (D-W d) of 1.485 for the refinement in space group Pmna, and by Rwp = 10.00 %, S = 1.367 and D-W d of 1.383 in space group Pma2, indicating that the fit of the former refinement is better than the latter. The refined Fe occupancies at the octahedral site in space groups Pmna and Pma2 are 0.16 ± 0.01 and 0.20 ± 0.01, respectively. In the Pmna-structure, the T2 site is occupied by Si0.5Al0.5 with disordering scheme, and average T2-O distance is 1.668 A. In contrast, in the Pma2-structure, Al and Si are distributed in an ordered state in the T2 site, and average AlT2-O and SiT2-O distances are 1.72 and 1.61 A, respectively. Absence of Fe3+ from the tetrahedral site may be attributed to the small size for the cation and inflexible character of the T2 site. A very small quadrupole splitting of the Mossbauer doublet by Fe3+ in the octahedral site suggests the octahedral site has a highly symmetrical site-geometry. This is consistent with a more symmetrical environment in the centrosymmetric space group Pmna.

Molecular structure of the molybdenum oxo-diperoxo compound MoO(O(2))(2)(OPy)(H(2)O): a computational and X-ray study.

We have carried out a combined experimental and theoretical study of the molecular structure of the MoO(O(2))(2)(OPy)(H(2)O) coordination compound using X-ray crystallography and DFT-B3LYP computational method, respectively. The MoO(O(2))(2)(OPy)(H(2)O) complex crystallizes in the orthorhombic space group Pmna with Z = 4, a = 6.9001(9) A, b = 8.0471(1) A, c = 16.227(2) A, V = 901.0(2) A(3), and the X-ray data analysis yields a bipyramidal-pentagonal coordination polyhedron for the Mo atom. The pyridine N-oxide (OPy) ligand occupies the equatorial position, with the oxygen atom of this ligand being located in the same plane as the four peroxo oxygen atoms. The H(2)O ligand is situated trans to the oxo group, forming intermolecular hydrogen bonds with peroxo groups belonging to two adjacent complexes. In our theoretical approach these intermolecular interactions were taken into account by including two methanol molecules which form hydrogen bonds with the water ligand leading to a good agreement between the calculated and the experimental geometry. Our results suggest that it is necessary to take into account the presence of these interactions in order to reconcile the theoretical results to the experimental data, in particular the distance between Mo and the oxygen of water ligand. These results seem to be a general feature for analogous bis-peroxo complexes that have been reported in the literature.

Quantum linear magnetic chains: structure and magnetic behavior of (2-methylpyrazine)copper(II) nitrate

The X-ray structure, susceptibility and magnetization of (2-methylpyrazine)copper(II) nitrate are reported. The compound crystallizes in the space group Pmna as a coordination polymer of Cu(II) ions bridged by 2-methylpyrazine. The resulting chains are magnetically well isolated and the susceptibility of the compound is well modeled as a one-dimensional Heisenberg antiferromagnet with 2 J=9.5(1) K. High-field magnetization studies to 30 T confirm the value of the exchange constant.

Spin frustration in MII[C(CN)3]2 (M = V, Cr). A magnetism and neutron diffraction study.

Three-dimensional coordination network solids of MII[C(CN)3]2 (M = V, Cr) composition possess interpenetrating rutile-like network structures. Each [C(CN)3]- bonds to three different metal ions in a triangular array, affording a geometrical topology akin to a Kagomé lattice leading to competing spin exchange interactions and spin frustration. The crystal and magnetic structure of CrII[C(CN)3] was determined by Rietveld refinement of the powder neutron diffraction data at 2 and 15 K and belongs to the orthorhombic space group Pmna [a = 7.313(1) A, b = 5.453(1) A, c = 10.640(1) A, Z = 2, T = 15 K]. Each CrII has a tetragonally elongated octahedral structure with four Cr-N(1) distances of 2.077(2) A and two significantly longer axial Cr-N(2) distances of 2.452(2) A. Magnetic susceptibility measurements between 1.7 and 300 K reveal strong antiferromagnetic interactions for both V- and Cr[C(CN)3]2 with theta = -67 and -46 K, respectively, from a fit to the Curie-Weiss law. Long-range magnetic ordering does not occur for M = V above 1.7 K, in contrast to M = Cr, which antiferromagnetically orders at low temperature. This is attributed to Jahn-Teller distorted CrII site relieving frustration in one dimension, leading to 2-D Ising antiferromagnetism, as observed by both magnetic susceptibility and specific heat studies. Neutron diffraction experiments at 2 K for Cr[C(CN)3]2 yielded additional Bragg reflections as a result of antiferromagnetic ordering with the moments on the CrII atoms aligned parallel to c and 4.7(1) microB. Fitting of the magnetic order parameter to a power law yielded TN = 6.12(4) K and beta = 0.18(1) consistent with 2-D Ising behavior. A TN of 6.13 K is also observed from the specific heat data.

Structural and Magnetic Properties of Cu[C(CN)3]2 and Mn[C(CN)3]2

Single-crystal X-ray structure analyses and the measurements of static magnetic susceptibility and ESR have been performed for the title compounds. Crystal data: for Cu[C(CN)3]2, space group Pmna, a = 7.212(5) A, b = 5.452(7) A, c = 10.696(7) A, and Z = 2; for Mn[C(CN)3]2, space group Pmna, a = 7.742(5) A, b = 5.411(6) A, c = 10.561(6) A, and Z = 2. Both salts are essentially isostructural. The Cu atoms are bridged by two [C(CN)3]- anions to form an infinite double chain structure, in which Cu has a square planar coordination (dCu-N = 1.986(6) A). The third CN end of the anion is weakly coordinated to the adjacent Cu chain (dCu-N = 2.47(1) A), making a three-dimensional network. The crystal is composed of two such interwoven networks. In the Mn complex, the third Mn−N distance (2.256(6) A) is as short as the equatorial coordinations (2.236(4) A), so that Mn is coordinated octahedrally. These compounds exhibit paramagnetic behavior following the Curie−Weiss law with Weiss temperatures −1.4 and −9 K, respe...

Synthesis and structural investigations of the double perovskites REBaFe2O5+w (RE=Nd, Sm)

P. Karen and P. M. Woodward, J. Mater. Chem., 1999, 9, 789 DOI: 10.1039/A809302D

Synthesis and Polymorphism of PdP2O6

Transparent needlelike brownish-yellow single crystals of PdP2O6 have been grown in air under P2O5-rich composition in the system PdO-P2O5. It crystallizes in the orthorhombic system, the possible space group Pmna or P2na, with a = 12.4904(9) Å, b = 4.5759(5) Å, c = 4.2344(3) Å, and Z = 2. This phase changes into a monoclinic phase under heating conditions. The quenchable monoclinic phase has the possible space group P 21/m or P21 with a = 13.156(2) Å, b = 5.1630(7) Å, c = 8.1426(9) Å, and β = 97.46(1)°. A transition temperature depends entirely on a heating rate, e.g., at 908°C at a rate of 10°C min-1, or over 660-735°C at a rate of 20°C hr-1. Moreover the monoclinic phase tends to be decomposed into Pd metal as the final product, depending on not only a temperature but a heating rate. Isothermal heat treatments show that the orthorhombic phase might be a metastable state and the monoclinic phase a stable state at lower temperatures.

Crystal structure of two isostructural tetramethyldioxapyrene salts

Abstract The crystal structures of two organic conductors di(3,5,8,10-tetramethyl-1,6-dioxapyrenium) tetrafluoroborate, (C18H16O2)+ 2 BF− 4, and di(3,5,8,10-tetramethyl-1,6-dioxapyrenium) hexafluorophosphate, (C18H16O2)+ 2 PF− 6, have been studied with single crystal X-ray diffraction methods. The two salts are isostructural and crystallize in the space group Pmna, Z = 2, with the unit cell parameters a = 6.772(1), b = 9.762(1) and c = 21.825(2) Å for the BF− 4 salt and a = 6.792(1), b = 9.769(1) and c = 22.096(3) Å for the PF[unk] salt. The models were refined to R-values of 0.082 (BF[unk]) and 0.069 (PF[unk]) using 860 and 979 reflections, respectively, with I> 2σ(I). The tetramethyldioxapyrene molecules lie on mirror planes stacked along the a-axis with an interplanar distance of exactly a/2 (3.386 and 3.396 Å for the BF[unk] and PF[unk] structure, respectively). The BF[unk] anion exhibits considerable disorder whereas the PF[unk] anion is ordered, which is reflected in the higher R-value for the BF[unk] structure. Both salts are semiconductors.

New layered ternary niobium tellurides: synthesis, structure, and properties of niobium metal telluride, NbMTe2 (M = iron, cobalt)

The layered ternary niobium tellurides NbMTe 2 (M=Fe, Co) have been synthesized by high-temperature solid-state reactions. The structures were determined by single-crystal X-ray diffraction methods, and both were found to be orthorhombic. NbFeTe 2 crystallizes in the space group Pmna (No.53) with Z=4, a=7.922 (1) A, b=7.239 (1) A, c=6.243 (1) A, V=357.98 (9) A 3 , and R=4.11%, R w =5.18%

ChemInform Abstract: Isolated Zirconium Chloride Clusters in the Phase Rb5Zr6Cl18B (I). Generalities Regarding the Bonding, Stability, and Size of M6X12‐Type Clusters with and without Interstitial Atoms.

Abstract(I) is prepared in high yield by reaction of Zr, B, RbCl, and ZrCl4 in a sealed Ta container at 850 °C. It crystallizes in the space group Pmna with Z=2.

The crystal structure of copper bromide triselenide, CuBrSe 3

The crystal structure of CuBrSe 3 has been determined. The compound is orthorhombic with unit cell dimensions a = 14.363 Å, b = 4.488 Å, c = 7.696 Å, Z = 4, and space group Pmna. Three-dimensional counterdiffraction intensity data (Mo Kα) were refined with block-diagonal and full-matrix least squares to a conventional unweighted R of 0.0515. The structure consists of six-membered selenium rings, in a chair-type configuration, separated in one axial direction by rows of bromine atoms and in the other by staggered layers of copper and bromine atoms. The rings are parallel to one another in rows along the c-direction, but the rows of rings alternate orientation in the a-direction.

Electron spectrum of NaF:Mn 2+: J.P. Srivastava, Department of Physics, Aligarh Muslim University, Aligarh 202001, India

The crystal structure of CuBrSe3 has been determined. The compound is orthorhombic with unit cell dimensions a = 14.363 Å, b = 4.488 Å, c = 7.696 Å, Z = 4, and space group Pmna. Three-dimensional counterdiffraction intensity data (MoKα) were refined with block-diagonal and full-matrix least squares to a conventional unweighted R of 0.0515. The structure consists of six-membered selenium rings, in a chair-type configuration, separated in one axial direction by rows of bromine atoms and in the other by staggered layers of copper and bromine atoms. The rings are parallel to one another in rows along the c-direction, but the rows of rings alternate orientation in the a-direction.

Application of group theory to the lattice dynamics of magnesium stannide

The germanides Sr7Ge6 and Ba7Ge6 as well as the stannide Ba3Sn2 were prepared by arc melting and annealing in welded tantalum ampoules using induction as well as resistance furnaces. The compounds were investigated by powder and single crystal X-ray diffraction. Sr7Ge6 and Ba7Ge6 crystallize in the Ca7Sn6 structure type (space group Pmna, Z=4: a=7.777(2) Å, b=23.595(4) Å, c=8.563(2) Å, wR2=0.081 (all data), 2175 independent reflections, 64 variable parameters for Sr7Ge6 and a=8.0853(6) Å, b=24.545(2) Å, c=8.9782(8) Å, wR2=0.085 (all data), 2307 independent reflections, 64 variable parameters for Ba7Ge6). Ba3Sn2 crystallizes in an own structure type with the space group P43212, Z=4, a=6.6854(2) Å, c=17.842(2) Å, wR2=0.037 (all data), 1163 independent reflections, 25 variable parameters.In Sr7Ge6 and Ba7Ge6 the Ge atoms are arranged as Ge2 dumbbells and Ge4 four-membered atom chains. Their crystal structures cannot be rationalized according to the (8-N) rule. In contrast, Ba3Sn2 presents Sn2 dumbbells as a main structural motif and thereby can be described as an electron precise Zintl phase. The chemical bonding situation in these structures is discussed on the basis of partial and total Density Of States (DOS) curves, band structures including fatbands, topological analysis of the Electron Localization Function (ELF) as well as Bader analysis of the bond critical points using the programs TB-LMTO-ASA and Wien2k. While Ba3Sn2 reveals semiconducting behaviour, all germanides Ae7Ge6 (Ae=Ca, Sr, and Ba) show metallic properties and a considerable π-bonding character between the Ge atoms of the four-membered chains and the dumbbells. The π-bonding character of the germanides is best reflected by the resonance hybrid structures {[Ge–Ge]6−/[Ge–....Ge–....Ge–....Ge]8−}↔{[Ge=Ge]4−/[Ge–Ge–Ge–Ge]10−}.