Acta Crystallographica Section B

Items from 1 to 20 out of 209 results

article

Concomitant polymorphic behavior of di‐μ‐thiocyanato‐κ²N:S;κ²S:N‐bis[bis(tri‐p‐fluorophenylphosphine‐κP)silver(I)]

Bernard Omondi, Reinout Meijboom

Acta Crystallographica Section B > 66 > 1 > 69 - 75

The structures of two polymorphs, both monoclinic P2₁/n [polymorph (I)] and P2₁/c [polymorph (II)], of di‐μ‐thiocyanato‐κ²N:S;κ²S:N‐bis[bis(tri‐p‐fluorophenylphosphine‐κP)silver(I)] complexes have been determined at 100 K. In both polymorphs the complex has a dinuclear structure where the silver(I) coordinates to two phosphine ligands and two bridging thiocyanate anions to form complexes with distorted...

article

Revision of the structure of Cs₂CuSi₅O₁₂ leucite as orthorhombic Pbca

A. M. T. Bell, K. S. Knight, C. M. B. Henderson, A. N. Fitch

Acta Crystallographica Section B > 66 > 1 > 51 - 59

The crystal structure of a hydrothermally synthesized leucite analogue Cs₂CuSi₅O₁₂ has been determined and refined using the Rietveld method from high‐resolution synchrotron X‐ray and neutron powder diffraction data. This structure is based on the topology and cation‐ordering scheme of the Pbca leucite structure of Cs₂CdSi₅O₁₂, and exhibits five ordered Si sites and one ordered Cu tetrahedrally coordinated...

article

Ab initio structure determination of phase II of racemic ibuprofen by X‐ray powder diffraction

Patrick Derollez, Emeline Dudognon, Frédéric Affouard, Florence Danède, more

Acta Crystallographica Section B > 66 > 1 > 76 - 80

Annealing of the quenched ibuprofen at 258 K yielded a new crystalline form, called phase II. Powder X‐ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position‐sensitive detector CPS120. The starting structural model was found by a Monte‐Carlo simulated annealing method. The final structure was obtained through...

article

Notes for authors 2010

Acta Crystallographica Section B > 66 > 1 > 104 - 108

article

A list of organic kryptoracemates

László Fábián, Carolyn Pratt Brock

Acta Crystallographica Section B > 66 > 1 > 94 - 103

A list of 181 organic kryptoracemates has been compiled. This class of crystallographic oddities is made up of racemic compounds (i.e. pairs of resolvable enantiomers) that happen to crystallize in Sohnke space groups (i.e. groups that include only proper symmetry operations). Most (151) of the 181 structures could have crystallized as ordered structures in non‐Sohnke groups. The remaining 30 structures...

article

Zur Kristallchemie von Graphen und Graphit

M. Trömel

Acta Crystallographica Section B > 66 > 1 > 81 - 83

The crystal structure of single‐layer graphene in comparison to graphite is discussed with regard to its crystallographic and chemical properties. In both of these polymorphs of carbon, the atomic volume of carbon, reduced to the closest packing of atoms, is practically the same and considerably smaller than in diamond. This indicates pentavalent carbon in graphene as well as in graphite. The observed...

article

Octahedral tilting in cation‐ordered Jahn–Teller distorted perovskites – a group‐theoretical analysis

Christopher J. Howard, Michael A. Carpenter

Acta Crystallographica Section B > 66 > 1 > 40 - 50

Computer‐based group‐theoretical methods are used to enumerate structures arising in A₂BB′X₆ perovskites, with either rock‐salt or checkerboard ordering of the B and B′ cations, under the additional assumption that one of these two cations is Jahn–Teller active and thereby induces a distortion of the BX₆ (or B′X₆) octahedron. The requirement to match the pattern of Jahn–Teller distortions to the cation...

article

Structures of dipeptides: the head‐to‐tail story

Carl Henrik Görbitz

Acta Crystallographica Section B > 66 > 1 > 84 - 93

The hydrogen‐bonding patterns in crystal structures of unprotected, zwitterionic dipeptides are dominated by head‐to‐tail chains involving the N‐terminal amino groups and the C‐terminal carboxylate groups. Patterns that include two concomitant chains, thus generating a hydrogen‐bonded layer, are of special interest. A comprehensive survey shows that dipeptide structures can conveniently be divided...

article

Structure solution of the new titanate Li₄Ti₈Ni₃O₂₁ using precession electron diffraction

Mauro Gemmi, Holger Klein, Amelie Rageau, Pierre Strobel, more

Acta Crystallographica Section B > 66 > 1 > 60 - 68

A sample having stoichiometry Li[Ti_1.5Ni_0.5]O₄ has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910 (1), c = 32.5371 (1) Å. The structure has been solved by direct methods working on a three‐dimensional set of intensities obtained from a precession electron‐diffraction...

article

Polysomatic apatites

Tom Baikie, Stevin S. Pramana, Cristiano Ferraris, Yizhong Huang, more

Acta Crystallographica Section B > 66 > 1 > 1 - 16

Certain complex structures are logically regarded as intergrowths of chemically or topologically discrete modules. When the proportions of these components vary systematically a polysomatic series is created, whose construction provides a basis for understanding defects, symmetry alternation and trends in physical properties. Here, we describe the polysomatic family A_5NB_3NO_9N + 6X_Nδ (2 ≤N≤∞) that...

article

A complicated quasicrystal approximant ɛ₁₆ predicted by the strong‐reflections approach

Mingrun Li, Junliang Sun, Peter Oleynikov, Sven Hovmöller, more

Acta Crystallographica Section B > 66 > 1 > 17 - 26

The structure of a complicated quasicrystal approximant ɛ₁₆ was predicted from a known and related quasicrystal approximant ɛ₆ by the strong‐reflections approach. Electron‐diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong‐reflections approach, the structure factors...

article

Structures of incommensurate and commensurate composite crystals Rb_xMnO₂ (x = 1.3711, 1.3636)

Jürgen Nuss, Steffen Pfeiffer, Sander Van Smaalen, Martin Jansen

Acta Crystallographica Section B > 66 > 1 > 27 - 33

Rb_1.3711MnO₂ (Rb₁₁Mn₈O₁₆) has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors Mn₂O₃, RbNO₃ and RbN₃. The structure of this extremely air‐ and moisture‐sensitive compound can best be described in terms of an incommensurate composite structure, built up by a honeycomb‐like framework of Rb ions, as one subsystem and by a second subsystem of chains, consisting...

article

Orientational disorder and phase transitions in crystals of dioxofluoromolybdate, (NH₄)₂MoO₂F₄

Anatoly A. Udovenko, Alexander D. Vasiliev, Natalia M. Laptash

Acta Crystallographica Section B > 66 > 1 > 34 - 39

Dioxotetrafluoromolybdate, (NH₄)₂MoO₂F₄, was synthesized in a single‐crystal form and its structures [(I) at 297 K and (II) at 223 K] were determined by X‐ray diffraction. Two independent states of a cis‐MoO₂F₄ octahedron are characteristic of static and dynamic disorder in structure (I). The dynamically disordered Mo atom is displaced from the symmetry axis producing four possible orientations of...

article

Predicted crystal structures of tetramethylsilane and tetramethylgermane and an experimental low‐temperature structure of tetramethylsilane

Alexandra K. Wolf, Jürgen Glinnemann, Lothar Fink, Edith Alig, more

Acta Crystallographica Section B > 66 > 2 > 229 - 236

No crystal structure at ambient pressure is known for tetramethylsilane, Si(CH₃)₄, which is used as a standard in NMR spectroscopy. Possible crystal structures were predicted by global lattice‐energy minimizations using force‐field methods. The lowest‐energy structure corresponds to the high‐pressure room‐temperature phase (, Z = 8). Low‐temperature crystallization at 100 K resulted in a single crystal,...

article

Mullite‐type Ga₄B₂O₉: structure and order–disorder phenomenon

Rihong Cong, Tao Yang, Kuo Li, Hongmei Li, more

Acta Crystallographica Section B > 66 > 2 > 141 - 150

Ga₄B₂O₉, an aluminium‐free mullite‐type compound, was prepared by a boric‐acid flux method and its structure was determined using powder X‐ray diffraction techniques, in combination with transmission electron microscopy, solid‐state ¹¹B MAS‐NMR and IR spectroscopies. GaO₆ octahedra share edges in a trans‐manner forming one‐dimensional chains along the b direction, and the chains are further cross‐linked...

article

l‐2‐Aminobutyric acid: two fully ordered polymorphs with Z′ = 4

Carl Henrik Görbitz

Acta Crystallographica Section B > 66 > 2 > 253 - 259

The crystal structure of l‐2‐aminobutyric acid, an l‐alanine analogue with an ethyl rather than a methyl side chain, has proved elusive owing to problems growing diffraction quality crystals. Good diffraction data have now been obtained for two polymorphs, in space groups P2₁ and I2, revealing surprisingly complex, yet fully ordered crystalline arrangements with Z′ = 4. The closely related structures...

article

Modulation functions of incommensurately modulated Cr₂P₂O₇ studied by the maximum entropy method (MEM)

Liang Li, Andreas Schönleber, Sander Van Smaalen

Acta Crystallographica Section B > 66 > 2 > 130 - 140

The maximum entropy method (MEM) has been used to determine electron density in superspace of incommensurately modulated chromium pyrophosphate from X‐ray diffraction data measured by Palatinus et al. [(2006), Acta Cryst. B62, 556–566]. Chromium pyrophosphate, Cr₂P₂O₇, contains ordered regions (83% of the volume) and regions with disorder. Analysis of the MEM density has allowed the determination...

article

Superspace description of the homologous series Ga₂O₃(ZnO)_m

Yuichi Michiue, Noboru Kimizuka

Acta Crystallographica Section B > 66 > 2 > 117 - 129

A unified description for the structures of the homologous series Ga₂O₃(ZnO)_m, gallium zinc oxide, is presented using the superspace formalism. The structures were treated as a compositely modulated structure consisting of two subsystems. One is constructed with metal ions and the other with O ions. The ideal model is given, in which the displacive modulations of ions are well described by the zigzag...

article

Re‐investigation of the structure and crystal chemistry of the Bi₂O₃–W₂O₆ `type (Ib)' solid solution using single‐crystal neutron and synchrotron X‐ray diffraction

Neeraj Sharma, Rene B. Macquart, Maxim Avdeev, Mogens Christensen, more

Acta Crystallographica Section B > 66 > 2 > 165 - 172

Single crystals of composition Bi_35.66W_4.34O_66.51 (or Bi_8.2WO_15.3, bismuth tungsten oxide), within the type (Ib) solid‐solution region of the Bi₂O₃–WO₃ system, were synthesized using the floating‐zone furnace method. Synchrotron X‐ray and neutron single‐crystal diffraction data were used to confirm the previously tentative assignment of the room‐temperature space group as I4₁. Fourier analysis of...

article

Inorganic structures in space group P31m; coordinate analysis and systematic prediction of new ferroelectrics

S. C. Abrahams

Acta Crystallographica Section B > 66 > 2 > 173 - 183

The 62 entries listed in ICSD release 2009/1 under polar space group P31m correspond to 31 families of inorganic crystal structures, some with only one member. Coordinate analysis reveals, over a wide confidence range, 11 of these families as ferroelectric candidates. One includes the well known improper ferroelectric GASH (guanidinium aluminum sulfate hexahydrate), [(C(NH₂)₃)Al(SO₄)₂(H₂O)₆], another...

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Keywords

POLYMORPHISM (21)
HYDROGEN BONDING (17)
X‐RAY POWDER DIFFRACTION (14)
PHASE TRANSITIONS (12)
DISORDER (11)
POWDER DIFFRACTION (9)
PHASE TRANSITION (8)
HYDROGEN BONDS (7)
CAMBRIDGE STRUCTURAL DATABASE (6)
DENSITY FUNCTIONAL THEORY (6)
ELECTRON DENSITY (6)
X‐RAY DIFFRACTION (6)
DIFFUSE SCATTERING (5)
MODULATED STRUCTURE (5)
NEUTRON DIFFRACTION (5)
TWINNING (5)
AMINO ACIDS (4)
NEUTRON POWDER DIFFRACTION (4)
BOND‐VALENCE MODEL (3)
CHARGE DENSITY (3)
COMPOSITE CRYSTAL (3)
CONFORMATIONAL POLYMORPHISM (3)
CRYSTAL PACKING (3)
DENSITY‐FUNCTIONAL THEORY (3)
ELECTRON DIFFRACTION (3)
ELECTRONIC STRUCTURE (3)
EXPERIMENTAL CHARGE DENSITY (3)
HIGH PRESSURE (3)
HYDROTHERMAL SYNTHESIS (3)
INTERMOLECULAR INTERACTIONS (3)
MALACHITE (3)
MULTIPOLE REFINEMENT (3)
NOTES FOR AUTHORS (3)
PEROVSKITES (3)
PHOTOCHROMISM (3)
PRESSURE (3)
RAMAN SPECTROSCOPY (3)
RIETVELD REFINEMENT (3)
STRUCTURE SOLUTION (3)
SYMMETRY (3)
SYNCHROTRON POWDER DIFFRACTION (3)
SYNCHROTRON RADIATION (3)
AROMATICITY (2)
AUTOMATED ELECTRON DIFFRACTION TOMOGRAPHY (2)
BASSANITE (2)
BOND‐VALENCE PARAMETERS (2)
BRIDGING FLUORINE ATOMS (2)
CALCIUM SULFATE SUBHYDRATE (2)
CARBONATES (2)
CATION ORDERING (2)
CHARGE‐DENSITY ANALYSIS (2)
CHIRALITY (2)
CONFORMATION (2)
CO‐CRYSTALS (2)
CRYSTAL STRUCTURE REFINEMENT (2)
DENSITY FUNCTIONAL CALCULATIONS (2)
DIFFERENTIAL SCANNING CALORIMETRY (2)
DINUCLEAR OXOFLUOROMETALLATES (2)
DRUG–RECEPTOR INTERACTION (2)
ENERGY CALCULATIONS (2)
FERROELECTRICS (2)
FORCE‐FIELD METHODS (2)
GROUP THEORY (2)
GYPSUM (2)
HARMONIC MODEL (2)
HIGH AIR HUMIDITY (2)
HIGH‐PRESSURE PHASE (2)
HOMOLOGOUS SERIES (2)
HOMOLOGOUS STRUCTURE (2)
INCOMMENSURATELY MODULATED STRUCTURE (2)
JAHN–TELLER DISTORTION (2)
JAHN–TELLER EFFECT (2)
LATTICE‐ENERGY MINIMIZATION (2)
MAXIMUM ENTROPY METHOD (2)
MEROHEDRAL TWINS (2)
MODULATED PHASE (2)
NMR SPECTROSCOPY (2)
OBITUARY (2)
OCTAHEDRAL TILTING (2)
ORDER–DISORDER (2)
PEROVSKITE (2)
PHARMACEUTICAL COCRYSTAL (2)
PHASE CHANGE (2)
PHASE SEQUENCE (2)
PZT (2)
SINGLE‐CRYSTAL DIFFRACTION (2)
SINGLE‐CRYSTAL X‐RAY DIFFRACTION (2)
SITE OCCUPANCY (2)
SUPERLATTICE (2)
SUPERSPACE FORMALISM (2)
SYNCHROTRON X‐RAY DIFFRACTION (2)
TOPOLOGICAL ANALYSIS (2)
TOPOLOGY (2)
VIBRATIONAL SPECTRA (2)
X‐RAY ANALYSIS (2)
X‐RAY CRYSTALLOGRAPHY (2)
11 X‐RAY WAVELENGTHS (1)
13C SOLID‐STATE NMR (1)
2‐QUINOLONE (1)
3,3T8 TOPOLOGY (1)
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Acta Crystallographica Section B

Concomitant polymorphic behavior of di‐μ‐thiocyanato‐κ²N:S;κ²S:N‐bis[bis(tri‐p‐fluorophenylphosphine‐κP)silver(I)]

Revision of the structure of Cs₂CuSi₅O₁₂ leucite as orthorhombic Pbca

Ab initio structure determination of phase II of racemic ibuprofen by X‐ray powder diffraction

Notes for authors 2010

A list of organic kryptoracemates

Zur Kristallchemie von Graphen und Graphit

Octahedral tilting in cation‐ordered Jahn–Teller distorted perovskites – a group‐theoretical analysis

Structures of dipeptides: the head‐to‐tail story

Structure solution of the new titanate Li₄Ti₈Ni₃O₂₁ using precession electron diffraction

Polysomatic apatites

A complicated quasicrystal approximant ɛ₁₆ predicted by the strong‐reflections approach

Structures of incommensurate and commensurate composite crystals Rb_xMnO₂ (x = 1.3711, 1.3636)

Orientational disorder and phase transitions in crystals of dioxofluoromolybdate, (NH₄)₂MoO₂F₄

Predicted crystal structures of tetramethylsilane and tetramethylgermane and an experimental low‐temperature structure of tetramethylsilane

Mullite‐type Ga₄B₂O₉: structure and order–disorder phenomenon

l‐2‐Aminobutyric acid: two fully ordered polymorphs with Z′ = 4

Modulation functions of incommensurately modulated Cr₂P₂O₇ studied by the maximum entropy method (MEM)

Superspace description of the homologous series Ga₂O₃(ZnO)_m

Re‐investigation of the structure and crystal chemistry of the Bi₂O₃–W₂O₆ `type (Ib)' solid solution using single‐crystal neutron and synchrotron X‐ray diffraction

Inorganic structures in space group P31m; coordinate analysis and systematic prediction of new ferroelectrics

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