Space Group Pcmn Research Articles

Study the oxygen vacancies and Fe oxidation states in CaFeO3-δ perovskite nanomaterial

CaFeO3-δ perovskite nanomaterial has been synthesized by sol-gel method. Rietveld analysis of the X-Ray diffraction (XRD) data of the CaFeO3-δ sample revealed orthorhombic perovskite structure (space group pcmn). Field emission scanning electron microscope (FE-SEM) of the CaFeO3-δ sample showed the agglomerations of various particles. Mössbauer measurement of the CaFeO3-δ sample showed that the value of δ is 0.262 and Fe oxidation states are Fe3+ in octahedral and Fe4+ in tetrahedral coordination. X-ray photoelectron spectroscopy (XPS) revealed that the presence of Fe3+, Fe4+ ions, and oxygen vacancies at the surface of the CaFeO3-δ sample. Thermogravimetry analysis (TG) and differential scanning calorimetric (DSC) of the CaFeO3-δ sample revealed the presence of phase transitions. The magnetic properties of the CaFeO3-δ sample exhibit mainly antiferromagnetic state as confirmed by Mössbauer measurement. Based on the obtained results, the presence of oxygen vacancies and mixed oxidation states of iron (Fe3+ and Fe4+) makes the CaFeO3-δ sample useful for industrial applications.

New Hybrid Material: (C3H6N3)4Bi2Cl10. Synthesis, Structural Study and Spectroscopic Behavior

The structure of (C3H6N3)4Bi2Cl10 was determined by single crystal X-ray diffraction at room temperature. It crystallizes in the orthorhombic space group Pcmn, with a = 9.430 (1) A, b = 17.426 (3) A, c = 19.883(5) A, V = 3267.3 (11) A3 and Z = 4. The structure consists of discrete binuclear [Bi2Cl10]4– anions and 3-aminopyrazolium cations. The crystal packing is governed by weak N–H···Cl hydrogen bonds, π–π and electrostatic Cl···Cl interactions. Infrared spectrum is used to gain more information on the title compound. An assignment of the observed vibration modes is reported. The crystal morphology is studied using the BFDH laws. The calculated HOMO and LUMO energies show that charge transfer occur within organic and inorganic molecules. The optical absorption of the zero-dimensional hybrid was also investigated.

Rare earth (Ce3+) activated NaMgF3 phosphor synthesised by hydrothermal method and its optical properties

In this paper, we present an environment friendly hydrothermal process to synthesize nano/sub micro particles of the rare earth activated complex fluoride NaMgF3 at 180 °C. The tittle compound synthesis was carried out at elevated pressure and temperature in an aqueous medium. The powder X-ray diffraction pattern was recorded to check the phase purity of the synthesised compound. Synthesized compounds were micro and nanocrystalline with orthorhombic perovskite crystal structure, space group Pcmn. In order to identify the functional groups Fourier Transform Infrared spectral analysis have been performed. The size and shape of the synthesised compounds were studied by using Field Emission - Scanning Electron Microscope images. Chemical composition of the synthesised compounds were checked by the energy - dispersive X-ray spectra. The absorption bands around 220 and 270 nm were observed which is corresponding to the electronic transition between 4f and 5d configuration of Ce3+. Photoluminescence emission related to the 5d→4f transitions in Ce3+ was observed at 324 nm. Thermoluminescence properties were studied for the X-ray irradiated samples. The glow curve kinetic parameters of activation energy (E) and frequency factor (S) were calculated using standard methods.

Determination of martensite structures of the Au7Cu5Al4 and Au7Cu5.7Al3.3 shape-memory alloys

The β-phase of Au7Cu5Al4 undergoes a reversible shape-memory phase transformation for which several conflicting martensite phases have been reported. Here we show the significance of the cooling temperature used to obtain the martensite. If Au7Cu5Al4 is cooled from the parent phase condition to cryogenic temperatures, e.g. below 200K, the martensitic phase is orthorhombic (space group Pcmn, a=4.4841Å, b=5.8996Å, c=17.8130Å); however, when this composition is cooled to only ∼260K it will in general consist of a mixture of orthorhombic and monoclinic phase (the latter has space group P21/m, a=4.4742Å, b=5.9265Å, c=13.3370Å, β=91.425°). In contrast, a sample with decreased Al content (Au7Cu5.7Al3.3) transforms fully to monoclinic phase if cooled to ∼260K.

THE CRYSTAL STRUCTURE OF CAVANSITE: LOCATION OF THE H2O MOLECULES AND HYDROGEN ATOMS IN Ca(VO)(Si4O10)*4H2O

Cavansite, Ca(VO)(Si4O10)•4H2O, is a novel layer silicate, dimorphous with pentagonite. The earlier determination of its structure did not yield the location of the hydrogen atoms or clear resolution of the oxygen atoms of the H2O molecules. In this study, structures are reported from data collected at 100(2) and 296(2) K, and they clearly resolve and allow refinement of the position of the H atoms. The 100 K and 296 K structures were refined to R 1 values of 0.0141 and 0.0389, respectively. Cavansite is orthorhombic with space-group symmetry Pcmn , with a 9.7518(4), b 13.6854(6), and c 9.5965(4) A at 100 K, and a 9.7614(7), b 13.6666(10), and c 9.6049(7) A at 296 K. Cavansite consists of two layers, a layer of silicate tetrahedra and a layer formed of irregular CaO4(OH2)4 polyhedra and VO5 square-based pyramids that alternate in ribbons parallel to [100] in (010); the layers join laterally at the four corners of the base of the V pyramid. The silicate layer consists of four- and eight-membered rings of silicate tetrahedra with apices pointing along [010] or [010]. The four oxygen atoms in the Ca polyhedron that are not linked to the V square-based pyramids are part of H2O molecules. Adjacent ribbons in (010) are linked by hydrogen bonding.

Palladium(II) Phosphotungstate Derivatives: Synthesis and Characterization of the [Pdx{WO(H2O)}3–x{A,α‐PW9O34}2](6+2x)– Anions

AbstractA series of PdII derivatives of the [P2W21O71(H2O)3]6– heteropolytungstate with the general formula [Pdx{WO(H2O)}3–x{A,α‐PW9O34}2](6+2x)– (x = 1–3) is described. These compounds are obtained by the reaction between [PdII(NO3)2]·H2O and the corresponding vacant polyoxometalates in water. They are characterized by IR and multinuclear NMR (31P and 183W) spectroscopy. Compound K10[Pd2{WO(H2O)}{A,α‐PW9O34}2]·30H2O was characterized by XRD: it crystallized in the orthorhombic space group Pcmn with parameters a = 18.119(3) Å, b = 19.729(3) Å, c = 24.856(5) Å, V = 8886(3) Å3.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Occupation Waves the Way You Have Never Seen Them: The Orthorhombic Quasicrystal Approximants RE13Zn58+δ (RE: Ho, Er, Tm and Lu).

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Occupation Waves the Way You Have Never Seen Them: the Orthorhombic Quasicrystal Approximants RE13Zn58+δ (RE = Ho, Er, Tm, and Lu)

A series of binary quasicrystal approximants RE13Zn58+delta (RE = Ho, Er, Tm, and Lu) have been prepared, and structural studies were performed by means of single-crystal X-ray diffraction. All four compounds crystallize in the orthorhombic system, but while the Ho-containing compound crystallizes in space group Pcmn, the rest of the compounds crystallize in Pc21n. This work is a continuation of the structural studies on RE13Zn approximately 58 (RE = Ce, Pr, Nd, Sm, Gd, Tb, and Dy), which all belong to the hexagonal system. The sequence of RE13Zn58+delta compounds exhibits a large variability in local ordering and composition, and therefore the crystal structures are generally rather more complex than those previously reported and exhibit a number of different ordering modes. These four compounds are structurally closely related to each other.

Crystal Structure of Cu3Bi(TeO3)2O2Cl: A Kagome Lattice Type Compound.

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Crystal structure of Cu 3Bi(TeO 3) 2O 2Cl: a Kagomé lattice type compound

Single crystals of Cu 3Bi(TeO 3) 2O 2Cl were synthesised via a transport reaction in sealed evacuated quartz glass tubes from a starting mixture of CuO, CuCl 2, Bi 2O 3, and TeO 2. The new compound Cu 3Bi(TeO 3) 2O 2Cl crystallizes in the orthorhombic space group Pcmn, a = 6.3179 ( 8 ) , b = 9.8524 ( 12 ) , c = 14.358 ( 2 ) Å , Z = 4 . Full matrix least squares refinement gave an R1 value of 0.0372 using 936 independent reflections. The structure is a layered compound where the building units are [Cu1O 4] square planes, [Cu2O 4Cl] square pyramids, [BiO 6+2] polyhedra, and [TeO 3E] tetrahedra (E being the 5s 2 lone pair of Te(IV)), joined through sharing of edges and corners. The Cu ions in the Cu O layers resemble a distorted Kagomé lattice. The Cu O planes are only connected by the two longest Bi O bonds (2.83 Å) in the [BiO 6+2] coordination polyhedra. The Cl ions and the Te lone pairs are located in tunnels in the structure along [001].

Crystal structure analysis of the orthorhombic phase II of KLiSO 4

The crystal structure of the orthorhombic high-temperature phase II (708–949 K) of KLiSO 4 was analyzed by single-crystal neutron diffraction. The ambiguity concerning the symmetry of this phase is solved and a disordered structure is established in the space-group Pcmn. Hence, KLiSO 4 II is confirmed to be isostructural to the highest-temperature modification I of RbLiSO 4.The investigated KLiSO 4 crystals were pseudohexagonally twinned with three ferroelastic domain states according to the phase transition from P6 3 (phase III at room temperature) to Pcmn (phase II).

Molecular Rhenium(V) Oxotransferases: Oxidation of Thiols to Disulfides with Sulfoxides. The Case of Substrate-Inhibited Catalysis.

Re(O)Cl(3)(PPh(3))(2), 1, and Re(O)Cl(3)(OPPh(3))(Me(2)S), 2, catalyze the oxidation of thiols to disulfides with sulfoxides under mild conditions. Catalyst 1 exhibits an induction period which features PPh(3) oxidation to OPPh(3) prior to disulfide formation. This lag is absent when 2 is the catalyst precursor. Otherwise, 1 and 2 display comparable kinetics and concentration dependencies. The catalytic reactions are first-order in catalyst, inhibited by thiol, and first-order in sulfoxide at low sulfoxide concentrations. Thiol inhibits the oxygen-transfer reaction because it competes with sulfoxide for coordination on rhenium. Sulfoxides must bind to rhenium in order to be activated for oxo transfer. Ligand substitution reactions of 1 and 2 display kinetics that are consistent with a dissociative (D) mechanism: the substitution rate is zero-order in entering ligand and inhibited by departing ligand. The first-order rate constant for the formation of a 5-coordinate intermediate is 0.06 s(-)(1). As the sulfoxide concentration is increased, the reaction rate increases to reach a maximum and then begins to decline. The catalytic turnover rate at optimal conditions (maximum k(cat) for PhS(O)Me is 180 h(-)(1)) approaches the rate of ligand substitution in these rhenium(V) complexes. Rate retardation at high sulfoxide concentrations is due to catalyst deactivation; sulfoxides oxidize the rhenium(V) catalyst to ReO(4)(-), which is inactive. Dimethyl sulfoxide (DMSO) is more efficient than aryl sulfoxides at oxidizing the catalyst, a fact that could be rationalized by the thermodynamics of S-O bond strength. Thus, aryl sulfoxides, such as PhS(O)Me, appear to be more reactive than alkyl ones. The oxygen-transfer reaction, therefore, is not involved in the rate-controlling step and the rate is limited by ligand substitution. The rhenium(V) catalyst in these reactions acts as a Lewis acid and activates the sulfoxide via coordination: the sulfoxide ligand and not the metal is the bearer of the transferred oxygen. A single-crystal X-ray structure of Re(O)Cl(3)(OPPh(3))(Me(2)S), 2, has been solved: space group Pcmn, a = 8.863(6) Å, b = 14.269(9) Å, c = 18.45(1) Å, Z = 4; the structure was refined to final residuals R = 0.028 and R(w) = 0.035.

High-Resolution X-Ray Powder Diffraction Studies of Some Mg- and Si- Substituted Brownmillerites

Structure refinements from powder diffraction data are presented for Ca2Fe1.4Mg0.3Si0.3O5 (I) and Ca2Fe1.07Al0.67Mg0.13Si0.13O5 (II). I has space group Pcmn, a 5.5961(1), b 14.7766(3), c 5.4273(1) �, Rwp = 12.5%, Rexp = 5.6%, RI = 8.7%; II has space group Ibm2, a 5.5815, b 14.5848(4), c 5.3711(1) �, Rwp = 13.2%, Rexp = 6.7%, RI = 9.3%;. Although the site occupancies were not successfully detd. for the latter, results confirm the anion-deficient perovskite structure for both compds. [on SciFinder(R)]

Solid-State Structure of Tp‘PtMe2H, a Dimethylhydrido Platinum(IV) Complex

The solid-state X-ray structure of Tp‘PtMe2H has been determined. This platinum(IV) hydride derivative is stable at room temperature and crystallizes in an orthorhombic cell (space group Pcmn, Z = 4, a = 8.1292(8) Å, b = 13.3862(9) Å, and c = 17.9670(16) Å). The hydride ligand was not located. The complex was synthesized as one of a series of organometallic platinum(IV) derivatives with Tp‘ (Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) in the coordination sphere. These octahedral platinum(IV) Tp‘PtMe2X and Tp‘PtPh2X complexes were prepared by formal oxidation of platinum(II) intermediates ([K][Tp‘PtMe2] and [K][Tp‘PtPh2]) with electrophiles (HX, MeI, I2). Thermogravimetric analysis (TGA) was employed to determine the solid-state decomposition temperatures for these platinum(IV) organometallic complexes.

Synthesis, Crystal Structure, and Optical and Thermal Properties of (C4H9NH3)2MI4 (M = Ge, Sn, Pb)

Single crystals of the organic-inorganic layered perovskites (C4H9NH3)2MI4 (M = Ge, Sn, Pb) have been grown from aqueous hydriodic acid solutions. X-ray diffraction, thermal analysis, and photoluminescence spectroscopy were used to compare crystal structure, metal atom lone-pair stereoactivity, and physical properties as a function of group IVB element. The orthorhombic (C4H9NH3)2GeI4 structure, refined in the space group Pcmn, consists of single-layer-thick perovskite sheets of distorted corner-sharing GeI6 octahedra separated by n-butylammonium cation bilayers. (C4H9NH3)2SnI4 and (C4H9NH3)2PbI4 are structurally very similar but adopt the space group Pbca, with a more ideal octahedral iodine coordination around the divalent group IVB atoms. Within the more general tin(II)-based family, (C4H9NH3)2(CH3NH3)n-1SnnI3n+1, a structural comparison between the title semiconducting n = 1 compound and the previously reported semimetallic n = 3 and metallic n → ∞ members demonstrates a correlation between perovskite...

Axial Site Occupancy by the Least Electronegative Ligands in Trigonal Bipyramidal Tetraoxyphosphoranes(1).

Analogous to the formation of CH(2)[(t-Bu)(2)C(6)H(2)O](2)P(Ph)(O(2)C(6)Cl(4)) (1), the new bicyclic tetraoxyphosphoranes CH(2)[(t-Bu)(2)C(6)H(2)O](2)P(Et)(O(2)C(6)Cl(4)) (3) and CH(2)[ClC(6)H(3)O](2)P(Ph)(O(2)C(6)Cl(4)) (4) were synthesized by the oxidative addition of the appropriate cyclic phosphines with o-tetrachlorobenzoquinone. For the formation of CH(2)[(t-Bu)(2)C(6)H(2)O](2)P(Ph)(O(2)C(2)Ph(2)) (2), a similar reaction was followed with the use of benzil (PhCOCOPh) in place of o-tetrachlorobenzoquinone. X-ray analysis of 1-3 revealed trigonal bipyramidal geometries and provided evidence for the first series of complexes in the absence of ring strain in which the least electronegative group, ethyl or phenyl, is located in an axial position, in violation of the electronegativity rule. Thus, the two oxygen-containing ring systems occupied two different sets of positions in the trigonal bipyramid (TBP) with the eight-membered rings at diequatorial sites. X-ray analysis of 4 revealed a trigonal bipyramidal geometry with electron-withdrawing chlorine substituents on each ring assumed the more conventional geometry with the rings occupying axial-equatorial positions and the phenyl group located in the remaining equatorial site. The fact that molecular mechanics calculations favorably reproduced the observed geometries suggests that a steric contribution associated with the ring tert-butyl groups for 1-3 is partly responsible in favoring diequatorial ring occupancy for the eight-membered ring. NMR data supported rigid pentacoordinated structures in solution at 23 degrees C. Phosphorane 1 crystallizes in the orthorhombic space group Fdd2 with a = 44.787(5) Å, b = 34.648(8) Å, c = 10.3709(9) Å, and Z = 16. Phosphorane 2 crystallizes in the orthorhombic space group Pna2(1) with a = 20.658(8) Å, b = 10.342(2) Å, c = 19.879(6) Å, and Z = 4. Phosphorane 3 crystallizes in the orthorhombic space group Pcmn with a = 9.807(2) Å, b = 16.632(4) Å, c = 23.355(3) Å, and Z = 4. Phosphorane 4 crystallizes in the monoclinic space group C2/c with a = 35.699(5) Å, b = 12.187(2) Å, c = 14.284(3) Å, beta = 107.08(1) degrees, and Z = 8. The final conventional unweighted residuals are 0.0395 (1), 0.0518 (2), 0.0540 (3), and 0.0868 (4).

A Reduced Neodymium Titanate with a New Intergrowth Structure Type

Single crystals of a new reduced neodymium titanate, Nd 3Ti 4O 12, have been obtained by slow cooling of a reduced Nd-Ti-O ceramic precursor in a molten neodymium borate flux under high vacuum. Single crystal X-ray diffraction (space group Pcmn, a = 5.420(1) Å, b = 7.610(1) Å, c = 22.015(5) Å, Z = 4, Pearson symbol oP76) showed that the structure of Nd 3Ti 4O 12 is built from an arrangement of corner-sharing and edge-sharing TiO 6-octahedra that can be considered as a regular intergrowth of the GdFeO 3 and CaTa 2O 6 structure types. The material is nonmetallic ( R(25°C) = 35 Ωcm) which may arise due to the localization of the Ti 3 d-electrons in the edge-sharing pairs of TiO 6-octahedra (short Ti-Ti distance of 2,760(3) Å).

Crystal and molecular structure of dipotassium-aquapentachlororhodate (III): (K2)++ [RhCl5(H2O)]2?

The structure of K2[RhCl5(H2O)] has been established by X-ray crystallography. It crystallizes in the orthorhombic space groupPcmn, with cell dimensionsa=7.065(1),b=9.453(1),c=13.567(1) A,V=906.1(3) A3,Z=4,Mr=376.4,Dx=2.76 g cm−3,F(000)=712,T=293 K. The final wasR=0.046. The rhodium atom has a distorted octahedral coordination involving five chlorine atoms and an oxygen of the water molecule with Rh, O, and three chlorine atoms on the mirror plane. Rh-Cl distances range from 2.284(7) A to 2.345(7) A. The Cl(4)⋯O intermolecular distance, 3.140(12) A indicates strong hydrogen bonding between oxygen and chlorine atoms of the neighboring octahedra.

Models for the phase diagrams of A2BX4and similar compounds

Abstract Incommensurate systems have been studied on a number of essentially onedimensional models. Examples are the ANNNI and the DIFFOUR models. These have one degree of freedom per site. The incommensurate phases of a large class of compounds with basic structure belonging to the space group Pcmn can qualitatively be understood with these models. Here two types of generalizations are discussed. First models with more degrees of freedom per site are studied. These give the possibility to restrict the range of the interactions. In the second place a coupling to elastic degrees of freedom is discussed. This may influence the type of phase transition. For strong enough coupling a second-order transition may turn into a first-order one.

Hafnium halide compounds of methyl substituted allyl ligands. Synthesis, crystal structure and dynamics of (η 5-C 5Me 5)(η 3-1,2,3-Me 3allyl)HfBr 2 and (η 5-C 5Me 5)(η 3-1,1,2-Me 3allyl)HfBr 2

The reaction of Cp *HfCl 3 with (1,2,3-Me 3allyl)MgBr or (1,1,2-Me 3allyl)MgBr and excess MgBr 2 yields Cp *(1,2,3-Me 3allyl)HfBr 2 and Cp *(1,1,2-Me 3allyl)HfBr 2. X-ray crystallography of these compounds shows a bent-metallocene-type geometry, with steric congestion in the asymmetrically methylated compound causing the greatest distortion yet observed of an η 3-allyl ligand towards an η 1binding mode for an early-transition metal complex. For Cp *(1,2,3-Me 3allyl)HfBr 2: cell constants a=14.581(7), b=14.725(8), c=8.291(3) Å; space group Pcmn; R=0.0425, R w=0.0397. For Cp *(1,1,2-Me 3allyl)HfBr 2: cell constants a=9.158(2), b=13.141(4), c=14.575(3) Å, β=101.06(2)°; space group P2 1/ n; R=0.0383, R w=0.0401. A variable temperature 1H NMR study indicates that the allyl ligand in (1,1,2-Me 3allyl)HfBr 2 undergoes η 3-η 1 isomerization (Δ G ‡(−53 °C)=40.9± 1 kJ/mol).