Space Group Pbcm Research Articles

Crystal Structure of the New Compound NdFeSb<sub>3</sub>

The crystal structure of a new compound NdFeSb3 has been determined by X-ray powder diffraction using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pbcm (No.57) with the CeNiSb3 structure type and lattice parameters a=1.26828(2)nm, b=0.61666(2)nm, c=1.81867(4) nm, z=12 and Dcalc=7.917g/cm3.

Discovery of β‐LnNiSb3 (Ln: La, Ce): Crystal Growth, Structure, and Magnetic and Transport Behavior.

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Discovery of β-LnNiSb3 (Ln = La, Ce): Crystal Growth, Structure, and Magnetic and Transport Behavior

A new polymorph of CeNiSb3 has been grown from a Sn flux and characterized by single-crystal X-ray diffraction. beta-CeNiSb3 crystallizes in the orthorhombic space group Pbcm (No. 57) with Z = 8. The unit cell parameters are a = 12.9170(2) A, b = 6.1210(5) A, c = 12.0930(6) A, and V = 956.13(9) A3. Its layered structure contains structural motifs similar to that of the first form of CeNiSb3 and consists of Ce atoms inserted between anionic layers of nearly square infinity2[Sb] nets and distorted infinity2[NiSb2] octahedra. We report the synthesis, magnetization, electrical resistivity, and specific heat of the new form of CeNiSb3 and compare the structures and physical properties of both polymorphs.

Syntheses, structures, and properties of Ag 4(Mo 2O 5)(SeO 4) 2(SeO 3) and Ag 2(MoO 3) 3SeO 3

Ag 4(Mo 2O 5)(SeO 4) 2(SeO 3) has been synthesized by reacting AgNO 3, MoO 3, and selenic acid under mild hydrothermal conditions. The structure of this compound consists of cis-MoO 2 2+ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that extended down the c-axis. Individual chains are polar with the C 2 distortion of the Mo(VI) octahedra aligning on one side of each chain. However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C 2 distortion. Upon heating Ag 4(Mo 2O 5)(SeO 4) 2(SeO 3) looses SeO 2 in two distinct steps to yield Ag 2MoO 4. Crystallographic data: (193 K; Mo Kα, λ=0.71073 Å): orthorhombic, space group Pbcm, a=5.6557(3), b=15.8904(7), c=15.7938(7) Å, V=1419.41(12), Z=4, R( F)=2.72% for 121 parameters with 1829 reflections with I>2 σ( I). Ag 2(MoO 3) 3SeO 3 was synthesized by reacting AgNO 3 with MoO 3, SeO 2, and HF under hydrothermal conditions. The structure of Ag 2(MoO 3) 3SeO 3 consists of three crystallographically unique Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO 6 units are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through tridentate selenite anions to form two-dimensional layers in the [ bc] plane. Crystallographic data: (193 K; Mo Kα, λ=0.71073 Å): monoclinic, space group P2 1 /n, a=7.7034(5), b=11.1485(8), c=12.7500(9) Å, β=105.018(1) V=1002.7(2), Z=4, R( F)=3.45% for 164 parameters with 2454 reflections with I>2 σ( I). Ag 2(MoO 3) 3SeO 3 decomposes to Ag 2Mo 3O 10 on heating above 550 °C.

Synthesis and Crystal Structure of 1-(2-Hydroxy-4-methoxyphenyl)-2-phenyl-1-ethanone

The title compound, C15H14O3, crystallizes in the orthorhombic system, space group Pbcm, with cell constants a = 9.751(3)A, b = 18.136(6)A, c = 7.004(2)A and Z = 4. The 1-(2-hydroxy-4-methoxyphenyl)ethanone part of the molecule is located on the crystallographic mirror plane. The strong intramolecular hydrogen bond O17-H17…O1 is observed. The molecular packing is influenced by the presence of π…π interactions.

Disproportionation of Pyrazine in NH+···N Hydrogen-Bonded Complexes: New Materials of Exceptional Dielectric Response

Centrosymmetric pyrazinium NH+...N bonded complexes allow their dielectric properties to be analyzed separately from the bulk ferroelectric polarization observed in the noncentrosymmetric DABCO monosalts. The method of dielectric permittivity measurements has been employed for monitoring polarization fluctuations generated by proton transfers in the NH+...N bonded linear polycations. The revealed dielectric response of [C4H5N2]+BF4- and [C4H5N2]+ClO4- cannot be reconciled with the centrosymmetric symmetry of their structures, but suggests formation of polar defects or nanoregions. Unique transformations of the pyrazine [C4H5N2]+BF4- complex between linear NH+...N hydrogen-bonded polycationic aggregates antiparallel in phase gamma, perpendicular chains in phase beta, and with NH+...N bonds broken in phase alpha have been observed. The [C4H5N2]+ClO4- and [C4H5N2]+BF4- complexes as grown at 290 K are isostructural in orthorhombic phase , space group Pbcm, with linear polycationic chains arranged antiparallel. On heating, the tetrafluoroborate and perchlorate salts each undergoes two first-order phase transitions at similar temperatures about 340-360 K, while on cooling only one phase transition has been observed. An extremely unique sequence of two phase transitions subsequently lowering the symmetry of the [C4H5N2]+BF4- crystal when temperature is increased has been evidenced: the orthorhombic phase heated above 343 K transforms into the monoclinic C2/c-symmetric phase beta, in which the NH+...N bonded linear chains assume perpendicular arrangement; and at about 353-357 K the anions and cations adopt a typical ionic-crystal packing without homonuclear NH+...N hydrogen bonds in a still lower-symmetry monoclinic P21/n-symmetric structure. The exceptional perpendicular arrangement of the linear NH+...N bonded chains in phase beta constitutes a unique system where polarization of small regions can assume various orientations within a plane, depending on the H+ sites. No phase transitions or anomalous dielectric response were observed in the NH+...O bonded [C4H5N2]+NO3- complex. The unprecedented structure-property relations of the pyrazinium complexes fully confirm the role of the NH+...N bond transformations for the dielectric response of analogous DABCO ferroelectrics.

Hybrid Organic−Inorganic Assemblies Based on Molybdates and Dimethyltin Linkers

Reaction of (CH3)2SnCl2 with Na2MoO4 in an aqueous medium results in three different compounds depending on the pH: [{(CH3)2Sn}(MoO4)] (1), [{(CH3)2Sn}4O2(MoO4)2] (2), and [{(CH3)2Sn}{Mo2O7(H2O)2}].H2O (3). All three species have been characterized in the solid state by means of elemental analysis, infrared spectroscopy, thermogravimetry, and single-crystal X-ray diffraction. Compounds 1-3 all show hybrid organic-inorganic extended lattices based on molybdate anions linked by (CH3)2Sn2+ moieties, and the coordination numbers of the Sn(IV) centers range from 5 to 7. Compound 1 crystallizes in the orthorhombic space group Pnma with cell parameters a = 13.2035(4) A, b = 7.2634(2) A, c = 7.1458(2) A, and Z = 4. 1 exhibits a complex, 3-dimensional network structure constructed of corner-shared, tetrahedral orthomolybdate oxoanions and distorted octahedral trans-(CH3)2SnO4 groups. Compound 2 crystallizes in the monoclinic space group P2(1)/n with cell parameters a = 8.2330(1) A, b = 11.4033(2) A, c = 12.1529(2) A, beta = 91.566(1) degrees , and Z = 2. Its 2-dimensional layered structure contains dimeric tetramethyldistannoxane [{(CH3)2Sn}4O2]2+ subunits built up of edge-sharing cis-(CH3)2SnO4 distorted trigonal bipyramids and connected in the (1,0,) plane by tetrahedral orthomolybdate oxoanions, the layers packing along the crystallographic a axis with the methyl groups pointing to the interlamellar space. Compound 3 crystallizes in the orthorhombic space group Pbcm with cell parameters a = 6.5594(4) A, b = 14.2465(11) A, c = 11.3892(8) A, and Z = 4. It shows dimeric [Mo2O8(H2O)2] units sharing corners to form zigzagging polymeric {[Mo2O7(H2O)2]2-}infinity polyanions along the [001] direction; these chains are further linked by trans-(CH3)2SnO5 distorted pentagonal bipyramids to give layers parallel to the (010) plane, the interlamellar space being occupied by hydrogen-bonded hydration water molecules.

Resolving the controversies about the ‘nearly cubic’ and other phases ofSr1−xCaxTiO3 (0≤x≤1): II. Comparison of phase transition behaviours forx = 0.40 and 0.43

The phase transition behaviour of two ‘nearly cubic’ compositions,x = 0.40 and 0.43, ofSr1−xCaxTiO3, representativeof Pbnm and Pbcm space group structures, has been investigated using temperature dependentdielectric, x-ray diffraction and Raman scattering techniques. Forx = 0.40, a first order antiferroelectric phase transition occurs around 364 K followed by anantiferrodistortive phase transition involving the R point () instability at ∼800 K. For x = 0.43, on the other hand, there is no antiferroelectric phase transition. Instead, twoantiferrodistortive transitions around 463 and 850 K linked with the M () and R () point instabilities, respectively, are observed. Both the compositions also exhibitqualitatively different types of phase transitions below room temperature.Evidence for a new phase transition at low temperatures is presented forx = 0.43.

23Na multiple-quantum MAS NMR of the perovskites NaNbO3and NaTaO3

The distorted perovskites NaTaO(3) and NaNbO(3) have been studied using (23)Na multiple-quantum (MQ) MAS NMR. NaTaO(3) was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO(3) were studied. The first, a commercially available sample which was annealed at 900 degrees C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.

Consolidation, Microstructure and Crystallography of Dense NaNbO<sub>3</sub> Ceramics with Ultra-Fine Grain Size

The present study reports on the preparation and structural characterization of dense NaNbO3 ceramics with ultrafine grain size. Nanocrystalline raw powders obtained via microemulsion mediated synthesis were consolidated to green compacts, sinterforged to ceramic pellets with high density and ultra-fine microstructure and finally annealed under different thermal regimes in order to systematically increase the average grain size in the range from several hundreds of urn up to a few mu m. Structural characterization of these materials included electron-microscopic observation and X-ray diffraction in combination with temperature tuning Raman-spectroscopy in order to detect both the global and local crystallographic symmetry in dependence of the grain size. The results show that ceramics with an average grain size from approximately 360 urn to 1-2 mu m consist of a phase mixture of the anti-ferroelectric phase with the space group Pbcm, which is also observed for the conventional case of coarse NaNbO3, and secondly of a new polar polymorph described by the space group Pmc2(1). The volume fraction of the second polar modification appears to increase with decreasing grain size suggesting an enhancement of the piezoelectric response of ultra-fine grained NaNbO3 ceramics in comparison to coarse grained material of the same composition.

Synthesis and crystal structure of the octahedral cluster complex [Th(DMSO)8Cl][Re6Se7Cl7

A cluster complex of the composition [Th(DMSO)8Cl][Re6Se7Cl7] has been obtained by interaction of ThCl4 solution in DMSO with a water solution of K3[Re6Se7Cl7] and KCl. The compound crystallizes in the rhombic space group Pbcm with unit cell parameters a = 12.262(2) A, b = 19.653(6) A, c = 23.603(6) A, V = 5688(2) A3, Z = 4, d calc = 3.282 g/cm3. The structure is built from centrosymmetric cluster anions [Re6Se7Cl7]3− and complex cations [Th(DMSO)8Cl]3+ possessing mirror-plane symmetry, half of the DMSO ligands being doubly disordered.

Investigation of the Y 2Te 3–Cu 2Te–PbTe system at 870 K and crystal structures of the Y 7Cu 3Te 12 and YCu 0.264Te 2 compounds

The phase equilibria in the Y 2Te 3–Cu 2Te–PbTe system at 870 K were determined. The formation of the YCuTe 2–Y 2/3Cu 2Te 2 compound (Er 2/3Cu 2S 2 structure type, space group P 3 ¯ , a = 0.42970(2) nm, c = 0.69087(5) nm, R I = 0.0582 for YCuTe 2) was observed. The crystal structures of new compounds Y 7Cu 3Te 12 (Ho 7Cu 3Te 12 structure type, space group R 3 ¯ m , Pearson symbol hR27-5, a = 0.43150(6) nm, c = 4.1790(8) nm, R1 = 0.0387) and YCu 0.264Te 2 (LaCu 0.28Te 2, space group Pbcm, Pearson symbol oP13.056, a = 0.7572(1) nm, b = 0.8164(1) nm, c = 0.6085(1) nm, R1 = 0.0597) were determined by means of X-ray single crystal diffraction. No quaternary compounds exist in the Y 2Te 3–Cu 2Te–PbTe system at 870 K.

Phase Equilibria and Crystal Structures of the Compounds in the Pr—Ni—Sb System at 870 K.

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Synthesis, Characterization, and Crystalline Structure of Syndiotactic 1,2-Polypentadiene: The Trans Polymer

(E)-1,3-Pentadiene was polymerized with the CoCl2(PiPrPh2)2−MAO system, obtaining a crystalline polymer with a melting point of 168 °C. The polymer was characterized by IR, NMR (13C and 1H in solution and 13C in the solid-state), DSC, GPC, and X-ray diffraction, and it was found to have a trans-1,2 syndiotactic structure. The fiber periodicity of 5.14 ± 0.03 Å indicates a trans-planar main-chain conformation similar to the one found in 1,2-syndiotactic polybutadiene. Molecular mechanics calculations using the MM2 force field show that, for trans-1,2 syndiotactic polypentadiene (t-12 sPPD), the all-trans main-chain conformation is more stable with respect to the (T2G2) arrangement, consistent with structural data of most 1,2-syndiotactic polydienes but at variance with the cis isomer and with 1,2-poly(4-methyl-1,3-pentadiene). The crystalline structure of t-12 sPPD has been determined on the basis of a unit cell derived from fiber data and refined using the Rietveld method on unoriented patterns. Like both 1,2-syndiotactic polybutadiene and 3,4-syndiotactic polyisoprene, it adopts the high-symmetry orthorhombic space group Pbcm with the following refined lattice parameters: a = 6.59(1), b = 14.69(1), and c (chain axis) = 5.11(3) Å. The two chains in the unit cell also present, besides crystallographic intramolecular glide planes, intramolecular 2-fold axes and planes of symmetry, both orthogonal to the glide plane. The main-chain conformation is slightly distorted from planarity, while the side chains adopt the same idealized skew arrangement found in other trans-1,2 syndiotactic polydienes. The refinement, giving the quality of the available data, is satisfactory. The thermal parameters, the relatively loose packing, and some features of the refined geometry points to disorder in the structure that we were unable to detail further using simple crystallographic models.

Synthesis and Characterization of Three Homoleptic Bismuth Silanolates: [Bi(OSiR3)3] (R = Me, Et,iPr)

The bismuth tris(triorganosilanolates) [Bi(OSiR3)3] (1, R = Me; 2, R = Et; 3, R = iPr) were prepared by reaction of R3SiOH with [Bi(OtBu)3]. Compound 1 crystallizes in the triclinic space group with Z = 2 and the lattice constants a = 10.323(1) A, b = 13.805(1) A, c = 21.096(1) A and α = 91.871(4)°, β = 94.639(3)°, γ = 110.802(3)°. In the solid state compound 1 is a trimer as result of weak intermolecular bismuth-oxygen interactions with Bi–O distances in the range 2.686(6)–3.227(3) A. The coordination at the bismuth atoms Bi(1) and Bi(3) is best described as 3 + 2 coordination whereas Bi(2) shows a 3 + 3 coordination. The intramolecular Bi–O distances fall in the range 2.041(3)–2.119(3) A. Compound 3 crystallizes in the orthorhombic space group Pbcm with Z = 4 and the lattice constants a = 7.201(1) A, b = 23.367(5) A and c = 20.893(1) A, whereas the triethylsilyl-derivative 2 is liquid. In contrast to [Bi(OSiMe3)3] (1) compound 3 is monomeric in the solid state, but shows similar intramolecular Bi–O distances in the range 1.998(2)–2.065(5) A. The bismuth silanolates are highly soluble in common organic solvents and strongly moisture sensitive. Compound 1 shows the lowest thermal stability.

Synthesis and Crystal Structure of a New Ternary Compound Ca4Al3Mg.

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Phase equilibria and crystal structures of the compounds in the Pr–Ni–Sb system at 870 K

The isothermal section of the Pr–Ni–Sb system at 870 K over the whole concentration region has been built using X-ray analysis. At the temperature of the investigation three already known ternary antimonides PrNiSb, ∼PrNiSb 2 and ∼PrNi 2Sb 2 have been confirmed and three compounds ∼Pr 5NiSb 2, PrNiSb 3, and PrNi 2+ x Sb 2− y have been synthesized for the first time. The crystal structures of the obtained compounds belong to the following structure types: PrNiSb–ZrBeSi type, space group P6 3/ mmc, a = 0.43838(2) nm, c = 0.81068(6) nm; PrNiSb 3–CeNiSb 3 type, space group Pbcm, a = 1.2579(2) nm, b = 0.62051(8) nm, c = 1.8371(2) nm; ∼Pr 5NiSb 2–structure related to Y 5Ni x Sb 3− x -type, space group Pnma, a = 1.2457(1) nm, b = 0.9159(1) nm, c = 0.8118(1) nm. The PrNi 2Sb 2 compound crystallizes with an orthorhombic or monoclinic unit cell and a structure related to the tetragonal CaBe 2Ge 2 type. The PrNi 2+ x Sb 2− y antimonide has a small homogeneity region and crystallizes with a tetragonal unit cell (space group P4/ nmm) and lattice parameters a = 0.431256(9) − 0.4319(1) nm, c = 0.99830(2) − 1.0092(3) nm. The existence of a considerable homogeneity region of the PrNi 0.62−1.35Sb 2 compound is caused by a deficiency of Ni atoms or their excess compared to the initial structure of stoichiometric composition and a corresponding transition from the HfCuSi 2 type to the CaBe 2Ge 2 type with preservation of the unit cell symmetry ( a = 0.43539(4) − 0.44130(2) nm, c = 0.9653(1) − 0.97643(5) nm).

Synthesis and crystal structure of a phthalate-bridged copper(II) complex {[Cu(L)(Phen)(H2O)]⋅H2O}n

A phthalate-bridged copper(II) complex {[Cu(phth)(Phen)(H2O)] ⋅ H2O}n (H2phth: phthalic acid, Phen: 1,10-phenanthroline) has been synthesized by the reaction of CuCl2 and phthalic acid in the presence of 1,10-phenanthroline in aqueous solution. The crystal structure of the complex has been determined by X-ray diffraction analysis to be orthorhombic, with the centrosymmetric space group Pbcm, where a = 11.6652(3) A, b = 11.1709(3) A, c = 14.0532(4) A, V = 1831.28(9) A3, Z = 4. The L2− (the acid radical of H2phth) ion is coordinated to the Cu2+ ion as a monodentate ligand. Each L2− ion bridges two adjacent Cu2+ ions with its two oxygen atoms from two carboxylic groups to form a one-dimensional zigzag chain. The coordination water and uncoordinated carboxylic oxygen atoms from neighboring chains are linked through hydrogen bonds to form a two-dimensional structure. There is a weak interaction between the coordination water molecule and the Cu2+ ion in the neighboring chain.

Structure and Physical Properties of Ternary Antimonide YbCrSb3

The ternary rare-earth antimonide YbCrSb3 was prepared by arc-melting of the elements. Its structure was determined by single-crystal X-ray diffraction (Pearson symbol oP20, orthorhombic, space group Pbcm, Z = 4, a = 12.981(3) Å, b = 6.140(1) Å, c = 5.993(1) Å). YbCrSb3 is isostructural to LaCrSb3 and CeCrSb3, and extends the RECrSb3 series (previously known for RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy) to the latest rare-earth member yet and to one that is essentially divalent instead of trivalent. Electrical resistivity measurements on single crystals and magnetic susceptibility measurements on powders revealed a magnetic ordering transition at TC = ∼280 K, the highest observed so far in the RECrSb3 series. The isothermal magnetization at 100 K indicated an approach to saturation, but with low values (0.08 μB/mol at 9 T). These results suggest a ferromagnetic or canted antiferromagnetic structure.

Electric modulus approach to the analysis of electric relaxation in highly conducting (Na0.75Bi0.25)(Mn0.25Nb0.75)O3 ceramics

Broadband dielectric spectroscopy is applied to investigate the electrical properties of disordered perovskite-like ceramics in a wide temperature range. From the x-ray diffraction analysis it was found that the newly obtained (Na0.75Bi0.25) (Mn0.25Nb0.75)O3 ceramics consist of two chemically different phases. The major perovskite one has an orthorhombic structure described by the Pbcm space group (No 57, in yxz setting). The minor phase shows an orthorhombic symmetry, all-face-centred lattice F, with the lattice parameters a = 10.797(4) Å, b = 7.601(3) Å and c = 7.691(3) Å. The electric modulus M* formalism used in the analysis enabled us to distinguish and separate the relaxation processes, dominated by marked conductivity in the ε*(ω) representation. In the ceramics studied, the relaxation times are thermally activated and the dipole process has a clearly non-Debye behaviour. The relaxation process described with the use of the activation energy of approximately 0.4 eV and the characteristic relaxation time, τ0 = 1 × 10−11 s, was found to be related to oxygen vacancies. The low frequency relaxation shows Debye behaviour with a slightly lower activation energy and a longer characteristic time.