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Growth and single-crystal refinement of phase-III potassium nitrate, KNO3Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Oriented single crystals of the high-temperature phase of KNO3 (phase III), a ferroelectric compound that may also occur as an atmospheric aerosol particle, were grown at room temperature and pressure by atomizing a solution of KNO3 in water and allowing droplets to dry on a glass substrate. The crystals are up to 1 mm across and are stable unless mechanically disturbed. There is no evidence of the spontaneous transformation of phase III to the room-temperature stable phase (phase II), even after several months. Single-crystal structure determinations of phase III were obtained at 295 and 123 K. The unit cell regained ...
Source: Acta Crystallographica Section B - November 19, 2009 Category: Chemistry Authors: Freney, E.J.Garvie, L.A.J.Groy, T.L.Buseck, P.R. Tags: aerosol particles explosives propellants polymorphism research papers Source Type: journals

Clara Brink Shoemaker (1921–2009)Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
(Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Abrahams, S.C.Hedberg, K. Tags: Obituaries Source Type: journals

[Ru(py)4Cl(NO)](PF6)2·0.5H2O: a model system for structural determination and ab initio calculations of photo-induced linkage NO isomers. ErratumEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In the paper by Cormary et al. [Acta Cryst. (2009), B65, 612–623] two authors were inadvertently omitted from the author list and one name was given incorrectly. (Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Cormary, B.Malfant, I.Valade, L.Buron-Le Cointe, M.Toupet, L.Todorova, T.Delley, B.Schaniel, D.Mockus, N.Woike, T.Fejfarová, K.Petříček, V.Dušek, M. Tags: metastable phases photocrystallography density functional calculations addenda and errata Source Type: journals

Towards a more reliable symmetry determination from powder diffraction: a redetermination of the low-temperature structure of 4-methylpyridine-N-oxideEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The low-temperature structure of 4-methylpyridine-N-oxide was previously determined in symmetry P41 [Damay et al. (2006), Acta Cryst. B62, 627–633]. Using a recently published symmetry-determination method it was found that the true symmetry of the structure is P41212. The structure was refined in the new space group using X-ray and neutron data. The previously published structure is close to the newly refined structure, but the new structure is in agreement with the results of rotational tunneling spectroscopy, and, in contrast to the structure in symmetry P41, does not require a twofold degeneracy of the tunneling band...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Palatinus, L.Damay, F. Tags: symmetry determination charge flipping powder diffraction short communications Source Type: journals

Space groups P1 and Cc: how are they doing?Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A survey of recent entries in the Cambridge Structural Database suggests that the percentage of structures described in space groups of inappropriately low symmetry has decreased from about 10% in the early 2000s to less than 5% today for space group Cc, but that for space group P1 it remains close to 8%. (Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Marsh, R.E. Tags: space groups Cambridge Structural Database low symmetry short communications Source Type: journals

How to easily replace the independent atom model – the example of bergenin, a potential anti-HIV agent of traditional Asian medicineEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Bergenin, which has been isolated from a variety of tropical plants, has several pharmacological applications in traditional Asian medicine. Its electron-density distribution was obtained from a room-temperature low-resolution X-ray data set measured with point detection making use of multipole populations from the invariom library. Two refinement models were considered. In a first step, positional parameters and ADPs were refined with fixed library multipoles (model E1). This model was suitable to be input into a second refinement of multipoles (model E2), which converged smoothly although based on Cu Kα room-temperatu...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Dittrich, B.Weber, M.Kalinowski, R.Grabowsky, S.Hübschle, C.B.Luger, P. Tags: bergenin refinement models density-functional calculations Hartree – Fock calculations independent atom model research papers Source Type: journals

Comparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transitionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), l-cysteic acid monohydrate (CAM) and S-4-sulfo-l-phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8 GPa. CAM contains bi-layers of l-cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stab...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Johnstone, R.D.L.Lennie, A.R.Parsons, S.Pidcock, E.Warren, J.E. Tags: layered hydrates high-pressure polymorphism phase transitions zwitterions research papers Source Type: journals

Molecular and crystalline structures of three (S)-4-alkoxycarbonyl-2-azetidinones containing long alkyl side chains from synchrotron X-ray powder diffraction dataEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The (S)-4-alkoxo-2-azetidinecarboxylic acids are optically active β-lactam derivatives of aspartic acid, which are used as precursors of carbapenem-type antibiotics and poly-β-aspartates. The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X-ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid-state, gas-phase den...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Seijas, L.E.Mora, A.J.Delgado, G.E.López-Carrasquero, F.Báez, M.E.Brunelli, M.Fitch, A.N. Tags: powder diffraction structure solution β -lactams hydrogen bonds research papers Source Type: journals

Experimental and theoretical charge-density study of a tetranuclear cobalt carbonyl complexEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Details of the complex bonding environment present in the molecular centre of an alkyne-bridged dicobalt complex have been examined using a combination of experimental and theoretical charge-density modelling for two compounds which share a central Co2C2 tetrahedral moiety as their common motif. Topological analysis of the experimental electron density illustrates the problem of separating the Co—C bond-critical points (b.c.p.s) from the intervening ring-critical point (r.c.p.), due largely to the flat nature of the electron density in the CoC2 triangles. Such a separation of critical points is immediately obtained from ...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Overgaard, J.Platts, J.A.Iversen, B.B. Tags: single-crystal X-ray diffraction charge-density distribution topological analysis theoretical structure factors research papers Source Type: journals

Cluster analyses of metal-organic fragments using the dSNAP softwareEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The dSNAP computer program has been used to classify searches of the Cambridge Structural Database for two ligands: —O—CH2—CH2—O— and N(CH2CH2O—)3 commonly found in metal-organic systems. The clustering method used is based on total geometries (i.e. all the lengths and angles involving all the atoms in the search fragment, whether bonded or not) and proved capable of distinguishing in a wholly automatic, objective way between different types of metal complex purely on the basis of the geometry of the ligand and the relative positions of the O atoms to the metals. (Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Collins, A.Wilson, C.C.Gilmore, C.J. Tags: cluster analysis dSNAP software Cambridge Structural Database research papers Source Type: journals

Isomorphism in monomeric 1:3 complexes of silver(I) salts with tri-p-tolylphosphineEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Reaction of silver(I) salts with three equivalents of tri-p-tolylphosphine in CH3CN resulted in a series of isomorphous complexes [AgX{P(4-MeC6H4)3}3] (X = Br, SCN, ClO4). These complexes all crystallize in the orthorhombic space group Pna21. The complexes with X = Br, SCN are distorted tetrahedral around the silver(I) atom, whereas the ClO4− complex is distorted trigonal planar around the silver. The new complexes are compared with each other using r.m.s. overlay calculations as well as half-normal probability plot analysis and with the previously reported isomorphous chloride, bromide as well as the non-isomorphous iod...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Omondi, B.Venter, G.J.S.Roodt, A.Meijboom, R. Tags: silver isomorphism phosphine half-normal probability research papers Source Type: journals

(111)p microtwinning in SrRuO3 thin films on (001)p LaAlO3Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
SrRuO3 (SRO) thin films grown on (001)p (p = pseudocubic) oriented LaAlO3 (LAO) by pulsed laser deposition have been characterized using transmission electron microscopy. Observations along the 〈100〉p directions suggests that although the SRO layer maintains a pseudocube-to-pseudocube orientation relationship with the underlying LAO substrate, it has a ferroelastic domain structure associated with a transformation on cooling to room temperature to an orthorhombic Pbnm phase (a−a−c+ Glazer tilt system). In addition, extra diffraction spots located at ±1/6(ooo)p and ±1/3(ooo)p (where `o' indicates an index with an ...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Han, Y.Reaney, I.M.Tinberg, D.S.Trolier-McKinstry, S. Tags: microtwinning pulsed laser deposition transmission electron microscopy superstructure reflections research papers Source Type: journals

Magnetic behaviour of synthetic Co2SiO4Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Synthetic Co2SiO4 crystallizes in the olivine structure (space group Pnma) with two crystallographically non-equivalent Co positions and shows antiferromagnetic ordering below 50 K. We have investigated the temperature variation of the Co2SiO4 magnetic structure by means of non-polarized and polarized neutron diffraction for single crystals. Measurements with non-polarized neutrons were made at 2.5 K (below TN), whereas polarized neutron diffraction experiments were carried out at 70 and 150 K (above TN) in an external magnetic field of 7 T parallel to the b axis. Additional accurate non-polarized powder diffractio...
Source: Acta Crystallographica Section B - November 16, 2009 Category: Chemistry Authors: Sazonov, A.Meven, M.Hutanu, V.Heger, G.Hansen, T.Gukasov, A. Tags: magnetic behaviour polarized neutron data symmetry research papers Source Type: journals

On the valences of bonds in the oxycomplexes of Sn2+Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The differences between Wang and Liebau's [Wang & Liebau (2007). Acta Cryst. B63, 216–228] stoichiometric valence (atomic valence) and structural valence (bond-valence sum) observed in Sn2+ and other lone-pair cation oxycomplexes arises from their use of the Brese & O'Keeffe bond-valence parameters which are based on the assumption that the bond-valence parameter b = 0.37 Å applies to all bond types. According to the theory of the bond-valence model, the bond-valence sum is necessarily equal to the ionic charge, implying that in the Wang and Liebau model the ionic charges are equal to the structural valence. If charge...
Source: Acta Crystallographica Section B - October 27, 2009 Category: Chemistry Authors: Brown, I.D. Tags: oxycomplexes atomic valence bond-valence sum research papers Source Type: journals

Weak intra- and intermolecular interactions in a binaphthol imine: an experimental charge-density study on (±)-8′-benzhydrylideneamino-1,1′-binaphthyl-2-olEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The charge density in (±)-8′-benzhydrylideneamino-1,1′-binaphthyl-2-ol (1) has been studied experimentally using Mo Kα X-ray diffraction at 100 K, and by theory using density-functional thoery (DFT) calculations at the B3LYP/6-311++G** level. The nature of the weak intramolecular peri-C...N, CH...π, H...H and C(π)...C(π) interactions has been examined by topological analysis using the Quantum Theory of Atoms in Molecules (QTAIM) approach. An analysis of the density ρ(r), the Laplacian of the density ∇2ρ(rb) and other topological properties at the bond-critical points were used to classify these interaction...
Source: Acta Crystallographica Section B - October 27, 2009 Category: Chemistry Authors: Farrugia, L.J.Kočovský, P.Senn, H.M.Vyskočil, Š. Tags: charge-density study density-functional theory topological properties bond-critical points inter- and intramolecular interactions research papers Source Type: journals

Octahedral tilt twinning and compositional modulation in NaLaMgWO6Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9 Å, which corresponds to a 12ap × 2ap × 2ap superstructure of the simple Pm\overline 3 m perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na...
Source: Acta Crystallographica Section B - October 27, 2009 Category: Chemistry Authors: King, G.Garcia-Martin, S.Woodward, P.M. Tags: twinning modulation neutron powder diffraction electron diffraction electron microscopy research papers Source Type: journals

A conformational polymorphic transition in the high-temperature ∊-form of chlorpropamide on cooling: a new ∊′-formEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Structural changes in the high-temperature ∊-polymorph of chlorpropamide, 4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S, on cooling down to 100 K and on reverse heating were followed by single-crystal X-ray diffraction. At temperatures below 200 K the phase transition into a new polymorph (termed the ∊′-form) has been observed for the first time. The polymorphic transition preserves the space group Pna21, is reversible and is accompanied by discontinuous changes in the cell volume and parameters, resulting from changes in molecular conformation. As shown by IR spectroscopy and X-ray powder dif...
Source: Acta Crystallographica Section B - October 27, 2009 Category: Chemistry Authors: Drebushchak, T.N.Chesalov, Y.A.Boldyreva, E.V. Tags: polymorphism chlorpropamide molecular conformation hydrogen bonds research papers Source Type: journals

Structure and conformational analysis of a bidentate pro-ligand, C21H34N2S2, from powder synchrotron diffraction data and solid-state DFTB calculationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The molecular and crystalline structure of ethyl 1′,2′,3′,4′,4a′,5′,6′,7′-octahydrodispiro[cyclohexane-1,2′-quinazoline-4′,1′′-cyclohexane]-8′-carbodithioate (I) was solved and refined from powder synchrotron X-ray diffraction data. The initial model for the structural solution in direct space using the simulated annealing algorithm implemented in DASH [David et al. (2006). J. Appl. Cryst. 39, 910–915] was obtained performing a conformational study on the fused six-membered rings of the octahydroquinazoline system and the two spiran cyclohexane rings of (I). The best model was chosen using exper...
Source: Acta Crystallographica Section B - September 16, 2009 Category: Chemistry Authors: Ávila, E.E.Mora, A.J.Delgado, G.E.Contreras, R.R.Rincón, L.Fitch, A.N.Brunelli, M. Tags: bioinorganic biomimetic nitrogen – sulfur pro-ligands direct space method powder diffraction conformational analysis density-functional tight-binding research papers Source Type: journals

[Ru(py)4Cl(NO)](PF6)2·0.5H2O: a model system for structural determination and ab initio calculations of photo-induced linkage NO isomersEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Structure analysis of ground state (GS) and two light-induced (SI and SII) metastable linkage NO isomers of [Ru(py)4Cl(NO)]·(PF6)2·0.5H2O is presented. Illumination of the crystal by a laser with λ = 473 nm at T = 80 K transfers around 92% of the NO ligands from Ru—N—O into the isomeric configuration Ru—O—N (SI). A subsequent irradiation with λ = 980 nm generates about 48% of the side-on configuration \rm Ru \lt ^N_O (SII). Heating to temperatures above 200 K or irradiation with light in the red spectral range transfers both metastable isomers reversibly back to the GS. Photodifference maps clearly show...
Source: Acta Crystallographica Section B - September 16, 2009 Category: Chemistry Authors: Cormary, B.Malfant, I.Buron-Le Cointe, M.Toupet, L.Delley, B.Schaniel, D.Mockus, N.Woike, T.Fejfarová, K.Petříček, V.Dušek, M. Tags: metastable phases photocrystallography density functional calculations research papers Source Type: journals

Superspace description of the modulated structure of the metal-salt-hybrid Bi7 − δNi2Br5 − 2δ (δ = 1/9)Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The compound Bi7 − δNi2Br5 − 2δ = (Bi3Ni)2[Bi1 − δBr4]Br1 −2δ (δ = 1/9) is a sub-bromide of the intermetallic phase Bi3Ni. Its crystal structure contains metallic rods, ^1_{\infty}[Bi3Ni], which are embedded in a salt-like matrix of bromido-bismuthate(III) and bromide anions. The non-stoichiometry originates from the variation of the number n of trans edge-sharing octahedra in the [BinBr4n + 2](n + 2)− oligomers (3 ≤ n ≤ 5), as well as from vacancies on the sites of the isolated Br atoms. The simplified structure is described in the orthorhombic space group Cmcm with a = 4.0660 (4...
Source: Acta Crystallographica Section B - September 16, 2009 Category: Chemistry Authors: Wahl, B.Ruck, M. Tags: modulated structure orientational disorder one-dimensional matrix research papers Source Type: journals

Modulated structure and phase transitions of Sr10Ga6O19Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The crystal structure of Sr10Ga6O19 was investigated by in situ single-crystal X-ray diffraction in the temperature range 298–673 K. At ambient conditions the compound shows a (3 + 1)-dimensional modulated structure in the superspace group C2/c(0β0)s0 [a = 34.9145 (13), b = 7.9369 (2), c = 15.9150 (7) Å and β = 103.551 (3)°] with a modulation wavevector of q = 0.4288 (2)b*. Whereas the presented structural model uses first-order harmonic modulation functions only, some features of the modulations are discussed utilizing an electron density derived by the maximum entropy method. Furthermore, two phas...
Source: Acta Crystallographica Section B - August 28, 2009 Category: Chemistry Authors: Krüger, H.Lazić, B.Arroyabe, E.Kahlenberg, V. Tags: modulated structures phase transitions incommensurate superstructure research papers Source Type: journals

Ternary fluorides BaMF4 (M = Zn, Mg and Mn) at low temperaturesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Ternary fluorides BaMF4 (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10 K using synchrotron and laboratory powder and single-crystal diffraction. The first two compounds are stable down to 10 K, while the third one undergoes a phase transition to an incommensurately modulated structure at approximately 250 K. The modulated phase is stable down to 10 K. The magnetic anomalies at 45 and 27 K observed previously in BaMnF4 are exclusively reflected in the behavior of the γ component of the q vector, which assumes an irrational value of approximately 0.395 Å−1 at the temperature corres...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Posse, J.M.Grzechnik, A.Friese, K. Tags: powder diffraction incommensurately modulated structures magnetic ordering research papers Source Type: journals

Eu3Si15 − xAl1 + xOxN23 − x (x ≃ 5/3) as a commensurate composite crystalEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A new Eu-SiAlON crystal, Eu3Si15 − xAl1 + xOxN23 − x (x ≃ 5/3), was found and the structure was determined by an X-ray diffraction technique using a twinned sample. The structure consists of a host framework, which is constructed by the connection of MX4 tetrahedra (M: Si or Al; X: O or N), and Eu ions as the guest ions. The structure is considered to be a commensurate composite crystal. The basic vectors are a1 = a/3, b and c for the first substructure, and a2 = a/5, b and c for the second substructure. The first substructure consists of part of the host framework and the Eu ions, while the remainder of ...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Michiue, Y.Shioi, K.Hirosaki, N.Takeda, T.Xie, R.-J.Sato, A.Onoda, M.Matsushita, Y. Tags: composite crystal superspace description twinning research papers Source Type: journals

Structure of caesium disulfate at 120 and 273 KEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The crystal structures of Cs2S2O7 at 120 and 273 K have been determined from X-ray single-crystal data. Caesium disulfate represents a new structure type with a uniquely high number of independent formula units at 120 K: In one part caesium ions form a tube surrounding the disulfate ions, [Cs8(S2O7)6+]n; in the other part a disulfate double-sheet sandwiches a zigzagging caesium ion chain, [Cs2(S2O7)6−]n. Caesium disulfate shows an isostructural order–disorder transition between 230 and 250 K, where two disulfate groups become partially disordered above 250 K. The Cs+-ion arrangement shows a remarkable similarit...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Ståhl, K.Berg, R.W.Eriksen, K.M.Fehrmann, R. Tags: caesium disulfate phase transition catalyst order – disorder research papers Source Type: journals

The experimental and theoretical QTAIMC study of the atomic and molecular interactions in dinitrogen tetroxideEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The atomic and molecular interactions in a crystal of dinitrogen tetraoxide, α-N2O4, have been studied in terms of the quantum topological theory of molecular structure using high-resolution, low-temperature X-ray diffraction data. The experimental electron density and electrostatic potential have been reconstructed with the Hansen–Coppens multipole model. In addition, the three-dimensional periodic electron density of crystalline α-N2O4 has been calculated at the B3LYP/cc-pVDZ level of theory with and without the geometry optimization. The application of the quantum theory of atoms in molecules and crystals (QTAIMC) r...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Tsirelson, V.G.Shishkina, A.V.Stash, A.I.Parsons, S. Tags: quantum-topological analysis electron density molecular complementarity electrostatic force field research papers Source Type: journals

Weak interactions in chain polymers [M(μ-X)2L2]∞ (M = Zn, Cd; X = Cl, Br; L = substituted pyridine) – an electron density studyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The experimental electron-density distributions in crystals of five chain polymers [M(μ-X)2(py)2] (M = Zn, Cd; X = Cl, Br; py = 3,5-substituted pyridine) have been obtained from high-resolution X-ray diffraction data sets (sin θ/λ > 1.1 Å−1) at 100 K. Topological analyses following Bader's `Atoms in Molecules' approach not only confirmed the existence of (3, −1) critical points for the chemically reasonable and presumably strong covalent and coordinative bonds, but also for four different secondary interactions which are expected to play a role in stabilizing the polymeric structures which are unusual for Zn ...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Wang, R.Lehmann, C.W.Englert, U. Tags: chain polymers electron density distribution topological analyses research papers Source Type: journals

Modulated crystal structure of incommensurate low tridymiteEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The incommensurately modulated crystal structure of low SiO2 tridymite was refined based on single-crystal X-ray diffraction data in the superspace group Cc(α0γ)0. The data set consists of 885 main reflections, 1751 first-order, 924 second-order and 119 third-order satellite reflections with I > 3σ(I). The modulation is mainly made up from cooperative twistings of the rigid SiO4 tetrahedra. Two orders of displacement waves are used to describe the modulation of the Si atoms and three orders for the O atoms. The maximal amplitudes are ca 0.6 Å. O atoms bridging pairs of tetrahedra in cis and trans configurations show ...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Graetsch, H.A. Tags: tridymite incommensurate modulation wavefunctions research papers Source Type: journals

Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM)Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ≃ 20 K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (lmax = 1) for the H atoms. Topological properties at bond critical points (BCPs) are f...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Netzel, J.van Smaalen, S. Tags: topological properties hydrogen bonding maximum entropy method charge densities peptides amino acids research papers Source Type: journals

Order–disorder of oxygen anions and vacancies in solid solutions of La2TiO5 and La4Ga2O9Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Successful Rietveld refinements of seven compounds with the formulae La2Ti(1−x)GaxO(5−x/2), where x = 0.00, 0.20, 0.50, 0.70, 0.90, 0.95 and 1.00, were performed in order to describe the solid solubility between orthorhombic (Pnam) La2TiO5 and monoclinic (P21/c) La4Ga2O9. The relationship between the end-member structures, which are already known, is discussed; the space-group change is a consequence of ordering the oxygen vacancies that become more numerous as Ga is substituted for Ti. The structures of the solid solutions are also described. The lengths of cell edges obey Vegard's rule. (Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Kasunič, M.Meden, A.Škapin, S.D.Suvorov, D.Golobič, A. Tags: solid solubility ternary system X-ray powder diffraction ordering of oxygen vacancies research papers Source Type: journals

Incommensurately modulated lanthanide coinage-metal diarsenides. II. GdCuAs2, GdAu1−δAs2 and TbAu1−δAs2 – new distortion variants of the HfCuSi2 type with irregularly stacked zigzag chains of arsenic atomsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
GdCuAs2, GdAu1−δAs2 and TbAu1−δAs2 crystallize as incommensurately modulated variants of the HfCuSi2 type. Structure models have been developed in the monoclinic superspace group P121/m1(α0γ)00 (No. 11.1). The components of the modulation wavevectors q = αa* + 0b* + γc* are α = 0.04 (1) and γ = 0.48 (1) for GdCuAs2, α = 0.03 (1) and γ = 0.48 (1) for GdAu1−δAs2 and α = 0.02 (1) and γ = 0.46 (1) for TbAu1−δAs2. The predominant effect of the positional modulation is the distortion of a square net of arsenic atoms, which results in planar zigzag chains. Rod groups and layer groups of the ...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Rutzinger, D.Bartsch, C.Doert, T.Ruck, M. Tags: incommensurately modulated structures distortion layered-type structures research papers Source Type: journals

Incommensurately modulated lanthanide coinage-metal diarsenides. I. CeAu1−δAs2 [δ = 0.015 (2)] – a new distortion variant of the HfCuSi2 type with irregularly stacked cis–trans chains of arsenic atomsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Rare-earth metal coinage-metal diarsenides LnTAs2 (Ln = Y, La, Ce–Lu; T = Cu, Ag, Au) are known to crystallize in structures closely related to the HfCuSi2 type, which comprises a stacking sequence of puckered TAs layers and planar square As nets, separated by the Ln atoms. CeAu1−δAs2, with δ = 0.015 (2), shows an incommensurate positional modulation of the arsenic atoms in the planar As nets. Based on X-ray diffraction data on a twinned crystal, a structure model in the monoclinic superspace group P121/m1(α0γ)00 (No. 11.1) with basic unit-cell parameters of a = 5.804 (1), b = 5.814 (1), c = 10.179 (1) Å...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Rutzinger, D.Doert, T.Ruck, M. Tags: incommensurately modulated structures twinning layered-type structures research papers Source Type: journals

Modulation of atomic positions in CaCuxMn7−xO12 (x ≤ 0.1)Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The modulation of atomic positions in CaCuxMn7−xO12 (x = 0 and 0.1) was studied using synchrotron radiation powder diffraction below 250 and 220 K, respectively. The copper-rich member CaCuxMn7−xO12 (x = 0.23) does not show any modulation of the atomic positions at temperatures as low as 10 K. Using low-temperature neutron powder diffraction the modulation of the magnetic moments of Mn ions in CaCuxMn7−xO12 (x = 0, 0.1 and 0.23) has been investigated. Long-range modulated magnetic ordering in CaCuxMn7−xO12 (x = 0, 0.1 and 0.23) is observed below 90.4, 89.2 and 78.1 K. (0,0,qp) and (0,0,qm) are the propagation...
Source: Acta Crystallographica Section B - August 27, 2009 Category: Chemistry Authors: Sławiński, W.Przeniosło, R.Sosnowska, I.Bieringer, M.Margiolaki, I.Suard, E. Tags: modulation synchrotron powder diffraction magnetic moments research papers Source Type: journals

Electron diffraction of ABX3 perovskites with both layered ordering of A cations and tilting of BX6 octahedraEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
It is shown that 21 ABX3 perovskites with tilted BX6 octahedra and layered ordering of A cations can be generated on the basis of group–subgroup relations. These structures (with 16 different space groups) are classified into ten diffraction types in terms of the conditions for superstructure reflections caused by the ordering of A cations, tilting of BX6 octahedra and structural absences. SAED (selected-area electron diffraction) allows the distinction of seven of the 21 different perovskites, while additional symmetry analysis by CBED (convergent-beam electron diffraction) is needed for the remaining 14 structures. The...
Source: Acta Crystallographica Section B - July 21, 2009 Category: Chemistry Authors: Kishida, K.Goto, K.Inui, H. Tags: crystal structure transmission electron microscopy electron diffraction perovskites research papers Source Type: journals

Structures of strontium diformate and strontium fumarate. A synchrotron powder diffraction studyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The crystal structures of strontium diformate in space groups P212121 (α form, 295 K), P41212 (β form, 334 and 540 K) and I41/amd (δ form, 605 K), and strontium fumarate in space groups Fddd (β form, 105 K) and I41/amd (α form, 293 K) have been determined from synchrotron X-ray powder diffraction data. Except for the α-strontium diformate, all the structures are based on a diamond-like Sr-ion arrangement, as in strontium acetylene dicarboxylate. The formate ions are disordered in the δ phase owing to steric hindrance. The fumarate ions are disordered over four (α) or two (β) symmetry-equivalent orientati...
Source: Acta Crystallographica Section B - July 15, 2009 Category: Chemistry Authors: Ståhl, K.Andersen, J.E.T.Shim, I.Christgau, S. Tags: synchrotron X-ray powder diffraction phase transitions research papers Source Type: journals

Structural elucidation of the Bi2(n + 2)MonO6(n + 1)(n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The cationic framework structure of a whole new family of compounds with the general formula Bi2(n + 2)MonO6(n + 1) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi10Mo3O24. These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all sh...
Source: Acta Crystallographica Section B - July 15, 2009 Category: Chemistry Authors: Landa-Cánovas, Á.R.Vila, E.Hernández-Velasco, J.Galy, J.Castro, A. Tags: ionic conductors bismuth – molybdenum oxides fluorite superstructures electron microscopy Aurivillius phase crystallographic shear research papers Source Type: journals

Trigonal structures of ABe2BO3F2 (A = Rb, Cs, Tl) crystalsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Several interesting fluoroberyllium borates were synthesized hydrothermally and characterized by single-crystal X-ray diffraction. The crystal structures of RbBe2BO3F2 (RBBF; rubidium fluoroberyllium borate) and CsBe2BO3F2 (CBBF; caesium fluoroberyllium borate), previously determined in the space group C2, were reinvestigated for higher symmetry and found to have more suitable solutions in the space group R32. TlBe2BO3F2 (TBBF; thallium fluoroberyllium borate) was synthesized as a novel compound also having this trigonal structure type. Details of the space-group determination and unique structural features are discussed. ...
Source: Acta Crystallographica Section B - July 15, 2009 Category: Chemistry Authors: McMillen, C.D.Hu, J.VanDerveer, D.Kolis, J.W. Tags: hydrothermal synthesis space-group determination physical morphology optical materials research papers Source Type: journals

Crystal structures and cation ordering in Cs2MgSi5O12, Rb2MgSi5O12 and Cs2ZnSi5O12 leucitesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The crystal structures of the leucite analogues Cs2MgSi5O12, Cs2ZnSi5O12 and Rb2MgSi5O12 have been determined by synchrotron X-ray powder diffraction using Rietveld refinement in conjunction with 29Si MAS NMR spectroscopy. These leucites are framework structures with distinct tetrahedral sites (T sites) occupied by Si and a divalent cation (either Mg or Zn in these samples); there is also a monovalent extra-framework cation (either Cs or Rb in these samples). The refined crystal structures were based on the Pbca leucite structure of Cs2CdSi5O12, thus a framework with five ordered Si T sites and one ordered Cd T site was us...
Source: Acta Crystallographica Section B - July 15, 2009 Category: Chemistry Authors: Bell, A.M.T.Henderson, C.M.B. Tags: leucites cation ordering 29Si NMR synchrotron radiation Rietveld refinement X-ray powder diffraction research papers Source Type: journals

Synthesis, crystal structure and spectroscopic properties of a novel carbacylamidophosphate: N-(3-nitrobenzoyl)-N′,N′′-bis(tert-butyl)phosphoric triamideEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The new compound N-(3-nitrobenzoyl)-N′,N′′-bis(tert-butyl)phosphoric triamide was synthesized by reacting 3-nitrobenzoyl phosphoramidic dichloride and tert-butyl amine, and characterized by multinuclear (1H, 13C and 31P) NMR and FTIR spectroscopy techniques. Structural and conformational properties were analyzed using single-crystal X-ray diffraction, vibrational spectra and theoretical calculations. The crystal structure contains three symmetry-independent disordered molecules, connected via intermolecular N—H...O=P and N—H...O=C hydrogen bonds to form a centrosymmetric hexameric chain extended along the [2,1,\b...
Source: Acta Crystallographica Section B - July 10, 2009 Category: Chemistry Authors: Gholivand, K.Mostaanzadeh, H.Koval, T.Dusek, M.Erben, M.F.Della Védova, C.O. Tags: phosphoric triamide hydrogen bonding disorder research papers Source Type: journals

Polymorphism in the spin-crossover ferric complexes [(TPA)FeIII(TCC)]PF6Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We have identified two polymorphs of the molecular complex [(TPA)Fe(III)(TCC)]PF6 [TPA = tris(2-pyridylmethyl)amine and TCC = 3,4,5,6-tetrachlorocatecholate dianion]: one is monoclinic and the other is orthorhombic. By lowering the temperature both undergo a thermal spin-crossover between a high-spin (S = 5/2) and a low-spin (S = 1/2) state, which we detected by magnetic, optical and X-ray diffraction measurements. The thermal crossover is only slightly shifted between the polymorphs. Their crystalline structures consist of similar cation layers alternating with PF6 anion layers, packed differently in the two polymorphs. T...
Source: Acta Crystallographica Section B - July 10, 2009 Category: Chemistry Authors: Collet, E.Boillot, M.-L.Hebert, J.Moisan, N.Servol, M.Lorenc, M.Toupet, L.Buron-Le Cointe, M.Tissot, A.Sainton, J. Tags: spin-crossover polymorphism phase transition research papers Source Type: journals

Inverse bilayer structure of mononuclear CoII and NiII complexes of the type M(H2O)3(SO4)(4-CNpy)2Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Two new metal compounds of the formula [M(H2O)3(SO4)(4-CNpy)2]·H2O [M = Ni (1) and Co (2), 4-CNpy = 4-cyanopyridine] have been prepared and studied by X-ray diffraction. In both of these compounds the 4-CNpy ligands are coordinated via pyridyl-N atoms to the metal ions in a cis fashion. The neutral complexes along with the uncoordinated H2O molecules are glued together preferentially into inverse bilayers by non-covalent interactions, including unique interlayer π–π interactions between antiparallel nitrile groups. Hartree–Fock and density-functional theory (DFT) calculations indicate that the π–π interactions a...
Source: Acta Crystallographica Section B - July 10, 2009 Category: Chemistry Authors: Das, B.K.Bora, S.J.Bhattacharyya, M.K.Barman, R.K. Tags: inverse bilayers X-ray powder diffraction hydrogen bonds research papers Source Type: journals

Atomic displacements at and order of all phase transitions in multiferroic YMnO3 and BaTiO3Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Coordinate analysis of the multiple phase transitions in hexagonal YMnO3 leads to the prediction of a previously unknown aristotype phase, with the resulting phase-transition sequence: P63′cm′(e.g.) ↔ P63cm ↔ P63/mcm ↔ P63/mmc ↔ P6/mmm. Below the Néel temperature TN ≃ 75 K, the structure is antiferromagnetic with the magnetic symmetry not yet determined. Above TN the P63cm phase is ferroelectric with Curie temperature TC ≃ 1105 K. The nonpolar paramagnetic phase stable between TC and ∼ 1360 K transforms to a second nonpolar paramagnetic phase stable to ∼ 1600 K, with unit-cell volume one-th...
Source: Acta Crystallographica Section B - July 10, 2009 Category: Chemistry Authors: Abrahams, S.C. Tags: atomic displacements phase transitions multiferroic compounds Landau theory research papers Source Type: journals

The incommensurately modulated crystal structure of β-Pb2BiVO6: interpretation of the phase transition α → β → δ and conduction properties of related materialsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A new polymorph of Pb2BiVO6 was prepared under ambient conditions and its crystal structure was determined by single-crystal X-ray diffraction. The phase transitions α → β and β → δ were identified in the mother phase; the high-temperature form δ-Pb2BiVO6 eventually decomposes at 753 K to a mixture of Pb4BiVO8 and the high-temperature form of PbBiVO5 before showing recombination at 923 K. β-Pb2BiVO6 has an incommensurate monoclinic modulated structure. This crystal structure is twinned and complementary structural investigations of a powder sample of β-Pb2BiVO6 by TEM diffraction studies confirmed the lattic...
Source: Acta Crystallographica Section B - July 10, 2009 Category: Chemistry Authors: Roussel, P.Labidi, O.Huve, M.Drache, M.Wignacourt, J.-P.Petricek, V. Tags: polymorphism phase stabilization incommensurately modulated structure oxide ionic conduction research papers Source Type: journals

Molecular Clusters. A Bridge to Solid-State Chemistry. By Thomas P. Fehlner, Jean-François Halet and Jean-Yves Saillard. Pp. xii + 378. Cambridge University Press, 2007. Price £70. ISBN 978-0-521-85236-4Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
(Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - June 12, 2009 Category: Chemistry Authors: Müller, U. Tags: book review book reviews Source Type: journals

Structures of the pseudo-trigonal polymorphs of Cu2(OH)3Cl. CorrigendumEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An error in the paper by Malcherek & Schlüter (2009), Acta Cryst. B65, 334–341, is corrected. (Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - June 12, 2009 Category: Chemistry Authors: Malcherek, T.Schlüter, J. Tags: clinoatacamite paratacamite herbertsmithite kagom è antiferromagnet addenda and errata Source Type: journals

On the polymorphism of benzocaine; a low-temperature structural phase transition for form (II)Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A low-temperature structural phase transition has been observed for form (II) of benzocaine (BZC). Lowering the temperature doubles the b-axis repeat and changes the space group from P212121 to P1121 with γ now 99.37 °. The structure is twinned, the twin rule corresponding to a 21 screw rotation parallel to a. The phase transition is associated with a sequential displacement parallel to a of zigzag bi-layers of ribbons perpendicular to b*. No similar phase transition was observed for form (I) and this was attributed to the different packing symmetries of the two room-temperature polymorphic forms. (Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - June 12, 2009 Category: Chemistry Authors: Chan, E.J.Rae, A.D.Welberry, T.R. Tags: polymorphism pharmaceuticals phase transitions twinning research papers Source Type: journals

Transferability and reproducibility in electron-density studies – bond-topological and atomic properties of tripeptides of the type l-alanyl-X-l-alanineEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In the last decade three different data bank approaches have been developed that are intended to make electron-density examinations of large biologically important molecules possible. They rely on Bader's concept of transferability of submolecular fragments with retention of their electronic properties. Therefore, elaborate studies on the quantification of transferability in experiment and theory are still very important. Tripeptides of the type l-alanyl-X-l-alanine (X being any of the 20 naturally encoded amino acids) serve as a model case between amino acids and proteins. The two experimental electron-density determinati...
Source: Acta Crystallographica Section B - June 12, 2009 Category: Chemistry Authors: Grabowsky, S.Kalinowski, R.Weber, M.Förster, D.Paulmann, C.Luger, P. Tags: tripeptides electron-density determinations transferability research papers Source Type: journals

Analysis of ion-migration paths in inorganic frameworks by means of tilings and Voronoi–Dirichlet partition: a comparisonEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Two methods using Voronoi–Dirichlet polyhedra (Voronoi–Dirichlet partition) or tiles (tiling) based on partitioning space are compared to investigate cavities and channels in crystal structures. The tiling method was applied for the first time to study ion conductivity in 105 ternary, lithium–oxygen-containing compounds, LiaXbOz, that were recently recognized as fast-ion conductors with the Voronoi–Dirichlet partition method. The two methods were found to be similar in predicting the occurrence of ionic conductivity, however, their conclusions on the dimensionality of conductivity were different in two cases. It is...
Source: Acta Crystallographica Section B - June 12, 2009 Category: Chemistry Authors: Anurova, N.A.Blatov, V.A. Tags: tiling Voronoi – Dirichlet partition ionic conductivity lithium compounds research papers Source Type: journals

A non-mathematical introduction to the superspace description of modulated structuresEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The X-ray analysis of (6R,7aS)-6-(tert-butyl-dimethylsilanyloxy)-1-hydroxy-2-phenyl-5,6,7,7a-tetrahydropyrrolizin-3-one, C19H27NO3Si, revealed a diffraction pattern which is typical for modulated structures: strong Bragg peaks surrounded by weaker reflections which cannot be indexed with the same three reciprocal lattice vectors that are used to describe the strong peaks. For this class of crystal structures the concept of superspace has been developed which, however, for many crystallographers still constitutes a Gordian Knot. As a possible tool to cut this knot the crystal structure of the above-mentioned tetrahydropyrro...
Source: Acta Crystallographica Section B - May 24, 2009 Category: Chemistry Authors: Wagner, T.Schönleber, A. Tags: molecular compound incommensurately modulated structure superspace teaching feature articles Source Type: journals

Structural Crystallography of Inorganic Oxysalts. By S. V. Krivovichev. Vol. 22, IUCr Monographs on Crystallography. Oxford University Press, 2009. Price (hardback) GBP 65.00. ISBN 978-0-19-921320-7.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
(Source: Acta Crystallographica Section B)
Source: Acta Crystallographica Section B - May 18, 2009 Category: Chemistry Authors: Liebau, F. Tags: book review book reviews Source Type: journals

A solution to the observed Z′ = 2 preference in the crystal structures of hydrophobic amino acidsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Chiral amino acids without functional groups in their side chains (hydrophobic amino acids) systematically form crystals with two molecules in the asymmetric unit. In contrast, racemates of the same compounds form crystals with Z′ = 1. The present investigation addresses the origin of this important difference between enantiomeric and racemic crystals. Through a series of ab initio calculations on infinite two-dimensional slabs, derived from crystal structures, as well as calculations on full crystal structures it is shown that it is indeed possible to explain the observed behaviour. Additionally, the (not unexpected) ob...
Source: Acta Crystallographica Section B - May 18, 2009 Category: Chemistry Authors: Görbitz, C.H.Vestli, K.Orlando, R. Tags: hydrophobic amino acids racemic crystals enantiomers energy calculations research papers Source Type: journals