Showing papers on "Orthorhombic crystal system published in 1978"
TL;DR: The mass fractions involved in the three phases can be derived directly from the integral intensities of characteristic bands without an additional calibration procedure as mentioned in this paper, and a comparison of the results obtained for a variety of samples shows agreement with the crystallinities derived from the density, and the small-angle and wide-angle x-ray diagrams.
Abstract: The Raman spectrum of partially crystalline polyethylene can be described as a superposition of three components, which originate from the orthorhombic crystalline phase, a meltlike amorphous phase, and a disordered phase of anisotropic nature, where chains are stretched but have lost their lateral order. The mass fractions involved in the three phases can be derived directly from the integral intensities of characteristic bands without an additional calibration procedure. A comparison of the results obtained for a variety of samples shows agreement with the crystallinities derived from the density, and the small-angle and wide-angle x-ray diagrams. Data indicate that the disordered anisotropic phase is located at a transition zone between crystalline and amorphous layers. Application of the method in a temperature-dependence experiment permits a detailed examination of partial melting.
448 citations
TL;DR: During the refinement, bond lengths and angles within each phosphate group and each rmcleoside were constrained exactly to their appropriate standard values, while those for the linkages between the nucleosides and phosphates were elastically restrained close to their standard values.
355 citations
TL;DR: The orthorhombic structures (Pbnm-Di~; No. 62) of GeS, GeSe, SnS and SnSe have been refined in this paper.
Abstract: The orthorhombic structures (Pbnm-Di~; No. 62) of GeS, GeSe, SnS and SnSe have been refined (X-ray diffractometer data: 319 hkl, R = 0.029; 370 hkl, R = 0.061 ; 386 hkl, R = 0.062; 506 hkl, R = 0.076). The bond distances are: Ge S = 2.438(1), 2.448(2) A; Ge-Se = 2.574(2),2.564(3) A; Sn-S = 2.665(2),2.627(4) A; SnSe = 2.793(2), 2.744(3) A. The structures of these compounds reveal systematic variations of bond lengths, bond angles and of nonbonding distances. These properties as well as their temperature dependence compared to those of related compounds allow to treat these structures as different configurations of a hypothetical reaction path of a phase transition GeS type ---+ TII type ---+ NaCl type.
247 citations
TL;DR: In this paper, a methodology for the study of the influence of crystal forces on molecular conformation has been developed and ap- plied, where a combination of quantitative analysis of the molecular pack- ing in different space groups along with ab initio molecular orbital calculations is used to analyze these phenomena.
Abstract: A methodology for the study of the influence of crystal forces on molecular conformation has been developed and ap- plied. As part of this study the phenomenon of conformationalpolymorphism, in which a molecule adopts significantly differ- ent conformations in different crystal polymorphs, is elucidated. A combination of quantitative analysis of the molecular pack- ing in different space groups along with ab initio molecular orbital calculations is used to analyze these phenomena. The model system p-(N-chlorobenzy1idene)-p-chloroaniline (a Schiff base) was chosen for study. Lattice energy calculations involving the minimization of the energy of the triclinic and orthorhombic crystal forms of this molecule were carried out in order to ex- plain the stability of the former lattice in which the unstable planar conformation of the molecule obtains. Three different po- tential functions were employed (6-9, 6- 12, and 6-exp), in order to avoid "potential-dependent" conclusions. All potentials yielded lower energies (more negative), for the triclinic lattice, in agreement with the experimental observation. The conforma- tional energy of the isolated molecule was studied by molecular orbital methods using both minimal and split valance basis sets. The energy differences obtained from these calculations are in good agreement with the differences in lattice energies obtained from the crystal calculations. A "partitioning" of the lattice energy into "partial atomic energies" was performed in order to carry out a detailed analysis of the packing differences between the polymorphs. The introduction of this partitioning proved to be a powerful probe for analyses of the energetics of different crystal packing modes. The approach employed, including packing analysis and crystal energetic studies to conformational polymorphs, yields much information as to the nature of the crystal forces in the different polymorphs and promises to be a useful tool in the investigation of the role of these forces in in- fluencing molecular conformation.
208 citations
01 Aug 1978
TL;DR: The perovskite-type synthetic clinoenstatite (MgSiO3) was converted to a single phase with the perov-skite structure in complete reactions at approx. 300 kbar in experiments that utilize the laser-heated diamond-anvil pressure apparatus as mentioned in this paper.
Abstract: Synthetic clinoenstatite (MgSiO3) has been converted to a single phase with the perovskite structure in complete reactions at approx. 300 kbar in experiments that utilize the laser-heated diamond-anvil pressure apparatus. The structure of this phase after quenching was determined by powder X-ray diffraction intensity measurement to be similar to that of the distorted rare-earth, orthoferrite-type, orthorhombic perovskites, but it is suggested that such distortion from ideal cubic perovskite would diminish at high pressure. The unit cell dimensions and density of perovskite-type MgSiO3 at ambient conditions (1 bar, 25°C) are a=4.780(1) A, b=4.933(1) A, c=6.902(1) A, V=162.75 A3, and ρ=4.098(1) g/cm3. This phase is 3.1% denser than the isochemical oxide mixture [periclase (MgO)+stishovite (SiO2)]. The small crystal-field stabilization energy of the cation site in the perovskite structure may play an important role in limiting the high-pressure stability field of perovskites that contain transition metal cations. Approximate calculations of the crystal-field effects indicate that perovskite of pure FeSiO3 composition may become stable at 400–600 kbar; pressures greater than 800 kbar would be required to stabilize CoSiO3 or NiSiO3 perovskite.
185 citations
TL;DR: In this paper, the crystal structure of Cu-Si precipitates in silicon has been determined based on a trigonally distorted b.c. arrangement, and the precipitates are shown to be of the equilibrium Cu3Si phase, probably of the low-temperature η” form.
Abstract: The crystal structure of Cu-Si precipitates in silicon has been studied by means of transmission electron diffraction and microscopy. The precipitates are shown to be of the equilibrium Cu3Si phase, probably of the low-temperature η” form. Consistent with earlier X-ray diffraction data for this phase, the crystal structure of the precipitates is determined to be based on a trigonally distorted b.c.c. arrangement. The lattice is orthorhombic (C), and is a two-dimensional long-period superlattice, which it is suggested is based on the intermediate-temperature η' phase; lattice parameters aη” = 76.76, bη” = 7.00, cη” = 21.94 A. On the basis of the diffraction data for the precipitates, it is suggested that the ηand η' phases are both trigonal, space groups R{\bar 3}m and R{\bar 3} respectively, with lattice parameters aη = 2.47 A, αη = 109.74° and aη' = 4.72 A, αη' = 95.72°.
180 citations
TL;DR: In this paper, a model for the structure of highly conducting polyacetylene-iodine complexes was proposed based on x-ray diffraction and spectroscopic results, and linear arrays of polyhalide ions (principally in the form of I−3) substitute in positions of displaced polyethylene chains.
Abstract: The structures of cis‐polyacetylene and polyacetylene–iodine derivatives have been investigated by x‐ray diffraction and crystal packing analysis. Results obtained for cis‐polyacetylene are consistent with the space group Pnma with one CH per asymmetric unit and a chain symmetry (m1)t. Hence, the structure is analogous to that of orthorhombic polyethylene. For a structure with such a concentration of π electrons there is minimal overlap between parallel π orbitals. The π orbitals are almost orthogonal for four of the six closest neighbors of a given chain. Based on x‐ray diffraction and spectroscopic results, a model is proposed for the structure of the highly conducting polyacetylene–iodine complexes. According to this model, linear arrays of polyhalide ions (principally in the form of I−3) substitute in positions of displaced polyacetylene chains. At high dopant concentrations, alternate close‐packed layers of polyacetylene are separated by a layer consisting of such polyhalide arrays. This model predi...
153 citations
TL;DR: The orthorhombic MgSiO3 perovskite has been synthesized with the aid of a double-stage split-sphere-type high-pressure apparatus at about 280 kbar and 1000°C.
148 citations
TL;DR: The antifungal antibiotic Rapamycin crystallises in the orthorhombic space group P212121 with a"="34.85(2), b" ="13.08(1), c''="12.25(1)''.
Abstract: The antifungal antibiotic Rapamycin crystallises in the orthorhombic space group P212121 with a = 34.85(2), b = 13.08(1), c = 12.25(1) A. The molecular structure has been determined by X-ray crysta...
127 citations
112 citations
TL;DR: In this paper, a methodology for the study of the influence of crystal forces on molecular conformation has been developed and ap- plied, where a combination of quantitative analysis of the molecular pack- ing in different space groups along with ab initio molecular orbital calculations is used to analyze these phenomena.
Abstract: A methodology for the study of the influence of crystal forces on molecular conformation has been developed and ap- plied. As part of this study the phenomenon of conformationalpolymorphism, in which a molecule adopts significantly differ- ent conformations in different crystal polymorphs, is elucidated. A combination of quantitative analysis of the molecular pack- ing in different space groups along with ab initio molecular orbital calculations is used to analyze these phenomena. The model system p-(N-chlorobenzy1idene)-p-chloroaniline (a Schiff base) was chosen for study. Lattice energy calculations involving the minimization of the energy of the triclinic and orthorhombic crystal forms of this molecule were carried out in order to ex- plain the stability of the former lattice in which the unstable planar conformation of the molecule obtains. Three different po- tential functions were employed (6-9, 6- 12, and 6-exp), in order to avoid "potential-dependent" conclusions. All potentials yielded lower energies (more negative), for the triclinic lattice, in agreement with the experimental observation. The conforma- tional energy of the isolated molecule was studied by molecular orbital methods using both minimal and split valance basis sets. The energy differences obtained from these calculations are in good agreement with the differences in lattice energies obtained from the crystal calculations. A "partitioning" of the lattice energy into "partial atomic energies" was performed in order to carry out a detailed analysis of the packing differences between the polymorphs. The introduction of this partitioning proved to be a powerful probe for analyses of the energetics of different crystal packing modes. The approach employed, including packing analysis and crystal energetic studies to conformational polymorphs, yields much information as to the nature of the crystal forces in the different polymorphs and promises to be a useful tool in the investigation of the role of these forces in in- fluencing molecular conformation.
TL;DR: In this article, the beta phase of FeTiD was shown to be orthorhombic with lattice parameters a=2.956+or-0.004 AA, b=4.543+or 0.006 AA, and c= 4.388+or -0.06 AA.
Abstract: The beta phase of FeTiD is shown to be orthorhombic with lattice parameters a=2.956+or-0.004 AA, b=4.543+or-0.006 AA and c=4.388+or-0.006 AA. The deuterium atoms are ordered on certain octahedral interstitial sites with two nearest-neighbour iron atoms.
TL;DR: In this article, a reversible order-disorder transition of strontium ferrate (III) took place and the compound had a statistically disordered oxygen-deficient perovskite structure with cubic symmetry.
TL;DR: In this article, three allotropic varieties of PbSnF4 -α, β and γ - have been detected by DTA and X-ray diffraction, and the α ai β and β ai γ transitions are reversible and occur at 80 and 355°C respectively.
TL;DR: The 18-crown-6 has a conformation with a pseudo-D3d symmetry as discussed by the authors, and the structure was solved by the conventional heavy-atom technique and refined by the full matrix least-squares method to R=0.099 for 1033 independent reflections.
Abstract: Ammonium bromide forms a 1 : 1 complex with cyclic polyether “18-crown-6.” The crystals of C12H24O6·NH4Br·2H2O are orthorhombic, with the space group of Pnam and with cell constants of a=10.002(3), b=12.716(4), c=15.073(4) A, and Z=4. The structure was solved by the conventional heavy-atom technique and refined by the full matrix least-squares method to R=0.099 for 1033 independent reflections. The 18-crown-6 has a conformation with a pseudo D3d symmetry. The ammonium cation is displaced by 1.00 A from the mean oxygen plane of the 18-crown-6 and interacts with the nearest bromide anion. The relationship between the cation and the 18-crown-6 resembles those of the C12H24O6·RbNCS and C12H24O6·CsNCS complexes. On the difference Fourier maps, four electron-density peaks were detected at reasonable positions for the hydrogen atoms of the amonium cation.
TL;DR: A survey of the known M 5 X 3 phases formed by the alkaline earth elements is given and the influence of the size factor on the occurrence of the various structural types is discussed as mentioned in this paper.
Abstract: The crystal structures of some M 5 X 3 compounds (M = Ca, Sr, Ba; f,X = element of Group II B, III B, IV B or V B) were determined by single crystal and powder techniques. The phases Ca 5 Zn 3 , Sr 5 Cd 3 , Ca 5 Ga 3 , Sr 5 In 3 , Sr 5 Tl 3 , Sr 5 Sn 3 , Ba 5 Sn 3 and Sr 5 Pb 3 crystallize with the tetragonal Cr 5 B 5 structure type; Ca 5 As 3 , Sr 5 As 3 , Ca 5 Sb 3 and Ba 5 Bi 3 belong to the hexagonal Mn 5 Si 3 type; Sr 5 Bi 3 is isostructural with orthorhombic β-Yb 5 Sb 3 . A survey of the known M 5 X 3 phases formed by the alkaline earth elements is given and the influence of the size factor on the occurrence of the various structural types is discussed.
TL;DR: In this article, the crystal structure of the high pressure metallic state of iodine has been determined by x-ray diffraction technique ultilizing a diamond-anvil high pressure cell combined with a position-sensitive proportional counter.
Abstract: The crystal structure of the high-pressure metallic state of iodine has been determined by x-ray diffraction technique ultilizing a diamond-anvil high-pressure cell combined with a position-sensitive proportional counter. Diffraction intensities measured at 206 kbar were very well interpreted by assuming the space group ${D}_{2h}^{18}$ which is the same as that at atmospheric pressure. With further increase in applied pressure, the structure will approach to a face-centered orthorhombic lattice formed by monoatomic iodine.
TL;DR: In this paper, the structure of α-CDx-sodium benzenesulfonate complex with m-nitrophenol (m-NP) was determined by the X-ray method.
Abstract: α-Cyclodextrin (α-CDx) forms a 1 : 2 crystalline complex with m-nitrophenol (m-NP). The crystal structure was determined by the X-ray method. The crystal is orthorhombic, and the space group is P21212 with Z=2. The cell dimensions are a=22.231(7), b=16.865(6), and c=8.152(1) A. The structure was solved on the basis of the nearly isomorphous structure of the α-CDx-sodium benzenesulfonate complex by using 2246 reflections, and refined by the block-diagonal least-squares method to the final R-value of 0.10. The framework of the crystal is built up of a stack of α-CDx molecules with a head-to-tail arrangement along the two-fold axis, showing a channeltype structure. Two m-NP molecules are statistically disordered on the two-fold axis. One is located in the channel, while the other is sandwiched between the α-CDx molecules. In the channel, the nitro group of m-NP is inserted into the α-CDx ring from the secondary hydroxyl side, and the phenolic hydroxyl group is hydrogen-bonded to the primary hydroxyl group of...
TL;DR: In this article, rare Earth orthophosphates have been synthesized and examined by X-ray diffraction, DTA and TGA, and six types have been found: a) the monazite type RPO4, b) the xenotime and weinschenkite types RPO 4·2H2O, e) the orthorhombic form DyPO4·1.5H 2O and f) the amorphous phosphate.
Abstract: Rare Earth orthophosphates have been synthesized and examined by X-ray diffraction, DTA and TGA. Six types have been found: a) the monazite type RPO4, b) the xenotime type RPO4, c) the hexagonal form RPO4·0.5H2O, d) the weinschenkite type RPO4·2H2O, e) the orthorhombic form DyPO4·1.5H2O and f) the amorphous phosphate.
TL;DR: An interesting finding was, that trypslnogen, the inactive precursor of trypsin is very similar in structure to trypsn ln about 85% of the molecule, but the rest is entirely different, and this part (the activation domain) shows no significant electron density in the electron density map oftrypsinogen indicating statistical or thermal disorder.
TL;DR: In this paper, the dispersion of the refractive index of tetragonal and ortorhombic bismuth trioxide thin films has been investigated using a single-oscillator model.
Abstract: Transmission spectra of bismuth trioxide thin films, of tetragonal and ortorhombic structures, are studied. Experimental data on the wavelength dependence of the refractive index are presented. The dispersion of the refractive index follows a single-oscillator model. Optical energy gap of tetragonal phase is smaller than that of orthorhombic phase; at 300 K these are 2.6 eV and 2.85 eV and at 77K are 2.8 and 3.1 eV, respectively.
TL;DR: In this paper, the M2X phases formed by the alkaline earth metals with the elements of Group IVB of the periodic system have been determined by the X-ray powder and single crystal methods.
Abstract: The M2X phases formed by the alkaline earth metals with the elements of Group IVB of the periodic system have been prepared and studied. Their crystal structure has been determined by the X-ray powder and single crystal methods. They crystallize in the orthorhombic anti-PbCl2 type (space group D162h). The relation between this structure and the Co2Si or anti-CaF2 structures, which occur for other homologous compounds formed by transition elements or magnesium, is discussed. The stability of these three types of structure as a function of atomic sizes, electronegativities and the electronic configuration of the valence shell of the component atoms is examined.
TL;DR: In this paper, a structural study of K2Cd2(SO4)3 is performed at 298, 351, 390.5, 417.5 and 443.5°K based on 3383, 1377, 1803, 1724 and 1022 symmetry independent structure factors.
Abstract: K2Cd2(SO4)3 is orthorhombic below 432°K, with space group P212121, and cubic above with space group P213. A structural study has been completed at 298, 351, 390.5, 417.5, and 443.5°K based, respectively, on 3383, 1377, 1803, 1724, and 1022 symmetry‐independent structure factors. Measurement of integrated intensities was made using a CAD‐4 diffractometer with Nb‐filtered MoKα radiation. An air‐flow microfurnace with temperature controller provided a thermal stability better than ±1°. The a, b, c lattice constants in the orthorhombic phase are 10.2084(8), 10.2813(8), 10.1684(8) A at 298°K; 10.2239(8), 10.2897(8), 10.1821(8) A at 351°K; 10.2386(8), 10.2951(8), 10.1981(8) A at 390.5°K; and 10.2501(10), 10.2972(8),10.2132(9) A at 417.5°K. In the cubic phase, a=10.2704(10) A at 443.5°K. The model previously obtained at room temperature [J. Chem. Phys. 67, 2146(1977)] was refined by the method of least squares using the new sets of measurements. The final agreement factors are R=0.028 (298°K), 0.032(351°K), 0.02...
TL;DR: In this paper, the crystal structure approximates and hexagonal sequence of close-packed chloride ion layers lying normal to c in which zinc ions occupy certain tetrahedral holes, and important interatomic distances and angles computed from the coordinates are listed.
Abstract: The crystal structure approximates and hexagonal sequence of close-packed chloride ion layers lying normal to c in which zinc ions occupy certain tetrahedral holes. Atom positions in the refined structure differ from those of the approximate model by at most 0.1 A. Important interatomic distances and angles computed from the coordinates are listed. Positional and thermal parameters with estimated standard deviations are tabulated. 1 figure, 2 tables.
TL;DR: In this article, the structural phase transitions in CsPbCl 3 and RbCdCl 3 have been investigated by 133 Cs and 87 Rb nuclear magnetic resonance (NMR).
Abstract: Structural phase transitions in CsPbCl 3 and RbCdCl 3 have been investigated by 133 Cs and 87 Rb nuclear magnetic resonance. The space groups of the room temperature phase in CsPbCl 3 and of two unknown phases in RbCdCl 3 could be clarified. Thus both perovskites show the same phase sequence from cubic Pm3m -O 1 h to tetragonal P4/mbm -D 5 4h orthorhombic Cmcm -D 17 2h and further orthorhombic Pnma -D 16 2h .
TL;DR: In this article, the spontaneous birefringence perpendicular to the polar axis of the orthorhombic low temperature phase has been measured versus temperature and silicon contents: the temperature of the phase transition of species 4mmFmm2 is of second order and decreases from 1103 K at 0 at %Si to about 400 K at 40 at % Si.
Abstract: Complete solid solubility is found in the pseudobinary system Ba2TiGe2O8-Ba2TiSi2O8 by studies on ceramics and single crystals (Czochralski technique). The spontaneous birefringence perpendicular to the polar axis of the orthorhombic low temperature phase has been measured versus temperature and silicon contents: the temperature of the phase transition of species 4mmFmm2 is of second order and decreases from 1103 K at 0 at % Si to about 400 K at 40 at % Si. The pyroelectric coefficient in the orthorhombic mm2 and the tetragonal 4 mm phase is of the order of 10−6 C m−2 K−1 in the entire system and has a positive temperature coefficient for all compositions studied except for Ba2TiGe2O8, in which the pyroelectric coefficient changes sign at about 308 K. The spacegroup of the orthorhombic phase is proposed to be C
2v
11
-Cmm2.
TL;DR: The crystal structure of µ-oxobis (cis-dichloro-cisdi(pyridine)-trans-oxorhenium(V)), ORe(C5H5N)2Cl2•O•Re( C5H 5N) 2Cl2O bas been studied by single crystal X-ray methods.
Abstract: The crystal structure of µ-oxobis(cis-dichloro-cis-di(pyridine)-trans-oxorhenium(V)), ORe(C5H5N)2Cl2•O•Re(C5H5N)2Cl2O bas been studied by single crystal X-ray methods. The crystals were orthorhombic with lattice parameters a = 15.367(2), b = 10.283(2), c = 16.685(2) A. The space group was Pna21 and there were four formula weights per unit cell. A total of 3339 reflections, of which 2990 were observed, were examined, and the structure refined by full matrix least squares (treating the pyridine rings as groups) to an R2 value of 0.0449. The dimer had a roughly rectilinear O—Re—O—Re—O backbone with pairs of chlorine atoms and pyridine molecules arranged cis in each half of the dimer. The two halves of the dimer were arranged such that the pairs of cis atoms in one half were rotated about the Re(1)–Re(2) axis almost 113 ° when compared to the corresponding pair in the other half. Important bond lengths (Re—O(terminal), 1.715(16), 1.764(16); Re—O(bridging), 1.943(16), 1.903(16); Re—Cl, 2.356(5)–2.390(5); Re—N,...
TL;DR: In this paper, the structure and molecular configuration of bis[N-(2-aminoethyl)salicylaldiminato] iron(III) chloride monohydrate, Fe(III)(Saen)2Cl·H2O, has been determined by X-ray diffraction techniques.
TL;DR: In this article, the crystal structure of (+)546-cis(O)-triammine(sarcosinate-N-propionato)cobalt(III) +)546ethylenediaminetetraacetato (ENEAT)coycycled carbon dioxide monohydrate was solved by single crystal X-ray diffraction techniques.
Abstract: The crystal structure of (+)546-cis(O)-triammine(sarcosinate-N-propionato)cobalt(III) (+)546-ethylenediaminetetraacetato)cobaltate(III) monohydrate was solved by single crystal X-ray diffraction techniques. The crystal is orthorhombic, space group P212121, with a=10.792, b=26.816, c=8.203 A, and Z=4. The final R value was 0.054. The absolute configurations of two complex ions were determined by means of anomalous dispersion using Cu Kα radiation. The coordinated asymmetric nitrogen atom of sarcosinate-N-propionate ligand takes an R configuration, and the (+)546-(ethylenediaminetetraacetato)cobaltate(III) ion Δ one.
TL;DR: The lattice parameter of the face-centered cell is 9.143 ± 0.001 A as discussed by the authors, consistent with a spinel structure analogous to cadmium indate.
Abstract: Bulk cadmium stannate, Cd2SnO4, normally crystallizes in the orthorhombic system. Cadmium stannate obtained from sputtered thin films and from a high-temperature, high-pressure procedure has now been shown, on the basis of an X-ray diffraction investigation, to crystallize in the cubic system. The lattice parameter of the face-centered cell is 9.143 ± 0.001 A. The data are consistent with a spinel structure, analogous to cadmium indate.