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CRYSTALLOGRAPHY (23 journals)

Showing 1 - 20 of 20 Journals sorted alphabetically
Acta Crystallographica Section A: Foundations and Advances     Hybrid Journal   (Followers: 8)
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials     Hybrid Journal   (Followers: 6)
Acta Crystallographica Section C: Structural Chemistry     Hybrid Journal   (Followers: 4)
Acta Crystallographica Section D : Biological Crystallography     Hybrid Journal   (Followers: 7)
Acta Crystallographica Section E : Crystallographic Communications     Open Access   (Followers: 3)
Acta Crystallographica Section F: Structural Biology Communications     Hybrid Journal   (Followers: 8)
Crystal Growth & Design     Hybrid Journal   (Followers: 13)
Crystal Research and Technology     Hybrid Journal   (Followers: 6)
Crystallography Reports     Hybrid Journal   (Followers: 2)
Crystallography Reviews     Hybrid Journal   (Followers: 3)
IUCrJ     Open Access  
Journal of Applied Crystallography     Hybrid Journal   (Followers: 7)
Journal of Chemical Crystallography     Hybrid Journal   (Followers: 2)
Journal of Crystal Growth     Hybrid Journal   (Followers: 6)
Liquid Crystals     Hybrid Journal   (Followers: 1)
Liquid Crystals Today     Hybrid Journal   (Followers: 1)
Materials and Devices     Open Access  
Molecular Crystals and Liquid Crystals     Hybrid Journal   (Followers: 1)
Polymer crystallization     Hybrid Journal  
Progress in Crystal Growth and Characterization of Materials     Full-text available via subscription   (Followers: 8)
Similar Journals
Journal Cover
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
Journal Prestige (SJR): 1.654
Citation Impact (citeScore): 5
Number of Followers: 6  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2052-5206 - ISSN (Online) 1600-5740
Published by IUCr Homepage  [10 journals]
  • The crystal structure of the first synthetic copper(II) tellurite
           arsenate, CuII5(TeIVO3)2(AsVO4)2

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      Authors: Missen; O.P., Weil, M., Mills, S.J., Libowitzky, E.
      Pages: 1 - 6
      Abstract: Crystals of the first synthetic copper tellurite arsenate, CuII5(TeIVO3)2(AsVO4)2 [systematic name pentacopper(II) bis-oxotellurate(IV) bis-oxoarsenate(V)], were grown by the chemical vapour transport method and structurally determined using single-crystal X-ray diffraction. CuII5(TeIVO3)2(AsVO4)2 possesses a novel structure type including a new topological arrangement of CuII and O atoms. CuII5(TeIVO3)2(AsVO4)2 is formed from a framework of two types of Jahn–Teller distorted [CuIIO6] octahedra (one of which is considerably elongated) and [CuIIO5] square pyramids, which are linked by edge-sharing to form chains and dimers and by corner-sharing to complete a three-dimensional framework. [AsVO4] tetrahedra and [TeIVO5] polyhedra bridge the edges of channels along the a-axis direction, with void space remaining for the TeIV stereoactive 5s2 lone pairs. A comparison is made between the crystal structure of CuII5(TeIVO3)2(AsVO4)2 and those of known compounds and minerals, in particular fumarolitic Cu minerals.
      Keywords: crystal structure; tellurite; arsenate; chemical transport reaction; fumarole
      Citation: urn:issn:2052-5206
      PubDate: 2020-02-01
      DOI: 10.1107/S2052520619014823
      Issue No: Vol. 76, No. 1 (2020)
       
  • Incommensurate crystal structure of PbHfO3

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      Authors: Bosak; A., Svitlyk, V., Arakcheeva, A., Burkovsky, R., Diadkin, V., Roleder, K., Chernyshov, D.
      Pages: 7 - 12
      Abstract: Controversy in the description/identification of so-called intermediate phase(s) in PbHfO3, stable in the range ∼420–480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma(00γ)s00 (No. 74.2). In contrast to some previously published reports, in the pure compound only one distinct phase was observed between Pbam PbZrO3-like antiferroelectric and Pm3m paraelectric phases. The modulation vector depends only slightly on temperature. The major structure modulation is associated with the displacement of lead ions, which is accompanied by a smaller amplitude modulation for the surrounding O atoms and tilting of HfO6 octahedra. Tilting of the octahedra results in a doubling of the unit cell compared with the parent structure.
      Keywords: perovskites; ferroic; diffraction; incommensurate
      Citation: urn:issn:2052-5206
      PubDate: 2020-02-01
      DOI: 10.1107/S205252061901494X
      Issue No: Vol. 76, No. 1 (2020)
       
  • The solubility and stability of heterocyclic chalcones compared with
           trans-chalcone

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      Authors: Sweeting; S.G., Hall, C.L., Potticary, J., Pridmore, N.E., Warren, S.D., Cremeens, M.E., D'Ambruoso, G.D., Matsumoto, M., Hall, S.R.
      Pages: 13 - 17
      Abstract: Heterocyclic chalcones are a recently explored subgroup of chalcones that have sparked interest due to their significant antibacterial and antifungal capabilities. Herein, the structure and solubility of two such compounds, (E)-1-(1H-pyrrol-2-yl)-3-(thiophen-2-yl)prop-2-en-1-one and (E)-3-phenyl-1-(1H-pyrrol-2-yl)prop-2-en-1-one, are assessed. Single crystals of (E)-1-(1H-pyrrol-2-yl)-3-(thiophen-2-yl)prop-2-en-1-one were grown, allowing structural comparisons between the heterocyclic chalcones and (2E)-1,3-diphenylprop-2-en-1-one, trivially known as trans-chalcone. The two heterocyclic chalcones were found to be less soluble in all solvents tested and to have higher melting points than trans-chalcone, probably due to their stronger intermolecular interactions arising from the functionalized rings. Interestingly, however, it was found that the addition of the thiophene ring in (E)-1-(1H-pyrrol-2-yl)-3-(thiophen-2-yl)prop-2-en-1-one increased both the melting point and solubility of the sample compared with (E)-3-phenyl-1-(1H-pyrrol-2-yl)prop-2-en-1-one. This observation may be key for the future crystal engineering of heterocyclic chalcones for pharmaceutical applications.
      Keywords: crystal structure; heterocyclic chalcones; solubility; thermal stability; intermolecular interactions; chalcones; crystals
      Citation: urn:issn:2052-5206
      PubDate: 2020-02-01
      DOI: 10.1107/S2052520619015907
      Issue No: Vol. 76, No. 1 (2020)
       
  • On the puzzling case of sodium saccharinate 1.875-hydrate: structure
           description in (3+1)-dimensional superspace

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      Authors: Rekis; T., Schönleber, A., van Smaalen, S.
      Pages: 18 - 27
      Abstract: The structure of sodium saccharinate 1.875-hydrate is presented in three- and (3+1)-dimensional space. The present model is more accurate than previously published superstructures, due to an excellent data set collected up to a high resolution of 0.89 Å−1. The present study confirms the unusual complexity of the structure comprising a very large primitive unit cell with Z′ = 16. A much smaller degree of correlated disorder of parts of the unit cell is found than is present in the previously published models. As a result of pseudo-symmetry, the structure can be described in a higher-dimensional space. The X-ray diffraction data clearly indicate a (3+1)-dimensional periodic structure with stronger main reflections and weaker superstructure reflections. Furthermore, the structure is established as being commensurate. The structure description in superspace results in a four times smaller unit cell with an additional base centring of the lattice, resulting in an eightfold substructure (Z′ = 2) of the 3D superstructure. Therefore, such a superspace approach is desirable to work out this high-Z′ structure. The displacement and occupational modulation of the saccharinate anions have been studied, as well as their conformational variation along the fourth dimension.
      Keywords: sodium saccharinate 1.875-hydrate; high-Z′ structures; superstructures; superspace; rigid-body modelling; commensurate structures
      Citation: urn:issn:2052-5206
      PubDate: 2020-02-01
      DOI: 10.1107/S2052520619014938
      Issue No: Vol. 76, No. 1 (2020)
       
  • Rb9–xAg3+xSc2(WO4)9: a new glaserite-related structure type, rubidium
           disorder, ionic conductivity

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      Authors: Spiridonova; T.S., Solodovnikov, S.F., Savina, A.A., Kadyrova, Y.M., Solodovnikova, Z.A., Yudin, V.N., Stefanovich, S.Y., Kotova, I.Y., Khaikina, E.G., Komarov, V.Y.
      Pages: 28 - 37
      Abstract: A new triple tungstate Rb9−xAg3+xSc2(WO4)9 (0 ≤ x ≤ 0.15) synthesized by solid state reactions and spontaneous crystallization from melts presents a new structure type related to those of Cs7Na5Yb2(MoO4)9 and Na13Sr2Ta2(PO4)9. The title compound in centrosymmetric space group Cmcm contains dimers of two ScO6 octahedra sharing corners with three bridging WO4 tetrahedra. Three pairs of opposite terminal WO4 tetrahedra are additionally linked by AgO2 dumbbells to form {Ag3[Sc2(WO4)9]}9− groups, which together with some rubidium ions are packed in pseudohexagonal glaserite-like layers parallel to (001), but stacking of the layers is different in these three structures. In the title structure, the layers stack with a shift along the b axis and their interlayer space contains disordered Rb+ cations partially substituted by Ag+ ions. Almost linear chains of incompletely filled close Rb3a–Rb3d positions (the shortest distances Rb–Rb are 0.46 to 0.64 Å) are found to locate approximately along the b axis. This positional disorder and the presence of wide common quadrangular faces of Rb2 and Rb3a–Rb3d coordination polyhedra favor two-dimensional ionic conductivity in the (001) plane with Rb+ and Ag+ carriers, which was confirmed with bond valence sum (BVS) maps. Electrical conductivity measurements on Rb9Ag3Sc2(WO4)9 ceramics revealed a first-order superionic phase transition at 570 K with a sharp increase in the electrical conductivity. The conductivity σi = 1.8 × 10−3 S cm−1 at 690 K is comparable with the value of 1.0 × 10−3 S cm−1 (500 K) observed earlier for rubidium-ion transport in pyrochlore-like ferroelectric RbNbWO6.
      Keywords: rubidium; silver; scandium; triple tungstate; synthesis; crystal structure; crystal chemistry; bond valence sum maps; ionic conductivity
      Citation: urn:issn:2052-5206
      PubDate: 2020-02-01
      DOI: 10.1107/S2052520619015270
      Issue No: Vol. 76, No. 1 (2020)
       
  • Rationalization of the crystal structure of eudidymite
           Na2Be2[Si[4]6O15]·H2O in light of the extended Zintl–Klemm concept

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      Authors: Vegas; A., Jenkins, H.D.B.
      Pages: 41 - 46
      Abstract: The structure of eudidymite is described in light of the extended Zintl–Klemm concept which considers that Na and Be atoms transfer their six valence electrons to the six Si atoms, converting them into Ψ-P which forms a skeleton characteristic of pentels (Group 15 elements) and is similar to that described in the compound (NH4)2Ge[6][Ge[4]6O15] when analysed in the same manner. The Si[4] skeleton is formed of bilayers that are connected through Be2O6 groups which are in fact fragments of the β-BeO structure which bridge the two contiguous Si-bilayers by sharing O atoms. In this context, the Be atoms play a dual role, i.e. on the one hand converting the Si atoms into Ψ-P, on the other hand replicating fragments of its own β-BeO structure. The Be atoms partially reproduce their own structure despite it being enclosed in a more complex network such as in Na2Be2[Si[4]6O15]·H2O. Calculations of the ionic strength I considering Si as Ψ-P is energetically more favourable than when I is calculated on the basis of tetravalent Si in the silicate, justifying this new approach of developing the theory of pseudo-structure generation. This approach offers a major new development in the study of crystal structures.
      Keywords: silicates; extended Zintl–Klemm concept; β-beryllia; ionic strength
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-11
      DOI: 10.1107/S205252061901549X
      Issue No: Vol. 76, No. 1 (2020)
       
  • Crystal structures of two very similar 2 × 2 × 2 superstructures
           of γ-brass-related phases in ternary Ir–Cd–Cu system

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      Authors: Ghanta; S., Roy, N., Jana, P.P.
      Pages: 47 - 55
      Abstract: A binary phase Ir8Cd41 in the Ir–Cd binary system and novel ternary phases in the Ir–Cd–Cu system have been synthesized from the constituent elements using high-temperature solid-state synthesis. The structure of previously reported Ir8Cd41 and newly found ternary phases in the Ir–Cd–Cu system have been characterized by single crystal X-ray diffraction and EDS analysis. The structural analysis reveals that Ir8Cd41 adopts V8Ga41-type structure and ternary Ir–Cd–Cu phases adopt two 2 × 2 × 2-superstructures of the γ-brass-related phase. The structures of ternary Ir–Cd–Cu phases are associated with structural disorder (vacancies as well as mixed site occupancies). The crystal structures of the ternary phases are viewed using layer description and cluster concept. The 2 × 2 × 2-superstructure of γ-brass-related phases in the Cu-poor region are not isostructural with the phases in the Cu-rich region, and they are consistent with the absence of a continuous phase region between two 2 × 2 × 2-superstructures of γ-brass-related phases. In the Cu-poor region, the structures contain ∼404 atoms per unit cell, whereas in the Cu-rich phases the structures contain ∼411 atoms in their respective unit cells. The crystal structures in the Cu-poor region represent a new type in the 2 × 2 × 2-superstructure of γ-brass-related phases in view of the combination of constituent cluster types, whereas the structures in the Cu-rich region adopt the Rh7Mg44 structure type.
      Keywords: complex intermetallic alloys; X-ray diffraction; superstructure; crystal structure; Ir–Cd–Cu system
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-15
      DOI: 10.1107/S2052520619015488
      Issue No: Vol. 76, No. 1 (2020)
       
  • A new high-pressure benzocaine polymorph — towards understanding the
           molecular aggregation in crystals of an important active pharmaceutical
           ingredient (API)

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      Authors: Patyk-Kaźmierczak; E., Kaźmierczak, M.
      Pages: 56 - 64
      Abstract: Benzocaine (BZC), an efficient and highly permeable anaesthetic and an active pharmaceutical ingredient of many commercially available drugs, was studied under high pressure up to 0.78 GPa. As a result, new BZC polymorph (IV) was discovered. The crystallization of polymorph (IV) can be initiated by heating crystals of polymorph (I) at a pressure of at least 0.45 GPa or by their compression to 0.60 GPa. However, no phase transition from polymorph (I) to (IV) was observed. Although polymorph (IV) exhibits the same main aggregation motif as in previously reported BZC polymorphs (I)–(III), i.e. a hydrogen-bonded ribbon, its molecular packing and hydrogen-bonding pattern differ considerably. The N—H...N hydrogen bonds joining parallel BZC ribbons in crystals at ambient pressure are eliminated in polymorph (IV), and BZC ribbons become positioned at an angle of about 80°. Unfortunately, crystals of polymorph (IV) were not preserved on pressure release, and depending on the decompression protocol they transformed into polymorph (II) or (I).
      Keywords: benzocaine; high-pressure polymorphism; data-mining; hydrogen bonds
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-16
      DOI: 10.1107/S2052520619016548
      Issue No: Vol. 76, No. 1 (2020)
       
  • Polymorphism of monotropic forms: relationships between thermochemical and
           structural characteristics

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      Authors: Perlovich; G., Surov, A.
      Pages: 65 - 75
      Abstract: In this work, a database containing thermochemical and structural information about 208 monotropic polymorphic forms has been created and analyzed. Most of the identified compounds (77 cases) have been found to have two polymorphs, 14 compounds have three forms and there are only three examples of systems with four polymorphs. The analysis of density distribution within the database has revealed that only 62 out of 114 metastable polymorphs (referred to as group I) obey the `density rule' proposed by Burger and Ramberger [(1979), Mikrochim. Acta, 72, 259–271], while the remaining 45% of the monotropic systems (group II) violate the rule. A number of physicochemical, structural and molecular descriptors have been used to find and highlight the differences between group I and group II of the polymorphs. Group II is characterized (on average) by higher values of descriptors, which are responsible for conformational flexibility of molecules. An algorithm has been proposed for carrying out bivariate statistical analysis. It implies partitioning the database into structurally related clusters based on Tanimoto similarity coefficients and subsequent analysis of each cluster in terms of the number of hydrogen bonds per molecule.
      Keywords: polymorphism; monotropic forms; melting temperature; fusion enthalpy; molecular crystals; similarity coefficient; clusterization; physicochemical descriptors
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-17
      DOI: 10.1107/S2052520619015671
      Issue No: Vol. 76, No. 1 (2020)
       
  • Compositely modulated structures of phosphor materials
           SrxLi2+xAl2–xO4:Eu2+

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      Authors: Ooishi; A., Michiue, Y., Funahashi, S., Takeda, T., Hirosaki, N.
      Pages: 76 - 84
      Abstract: Composite crystals SrxLi2+xAl2−xO4:Eu2+ were synthesized and their structures were determined using single-crystal X-ray diffraction. The commensurate structure with a modulation wavevector q = 5c*/6 was analyzed in a conventional manner in 3D space, while a structure model in (3+1)-dimensional superspace was used for the other two crystals with modulation wavevectors slightly differing from 5c*/6. The superstructure of the commensurate phase was described using the space group P4/n and a common superspace group I4/m(00γ)00 was used for the (3+1)D structures of all three crystals. The whole structure of each crystal consists of two substructures. Basis vectors a and b are common, but c is different for the two substructures. The first substructure is a host framework constructed by (Li/Al)O4 tetrahedra sharing edges. A linear connection of cavities is seen to be channel-like, in which Sr ions locate as guest cations forming the second substructure. The crystal of q = 5c*/6 contains five Sr ions per six cavities in a channel. Sr ions are distributed at seven sites, some of which are partially occupied. Statistical disorder of local structure models for the location of Sr ions in the channel was assumed to explain the results. Such a partially disordered character was also seen in the incommensurate phases and properly embodied by a (3+1)D model containing an atomic domain of the Sr ion with occupational modulation. Plots of the occupation factor, interatomic distances and the bond valence sum at each metal site as functions of t (= x4 − q·r) are roughly identical in the three crystals, which are considered as members of the same series of composite crystals.
      Keywords: composite crystal; modulated structure; strontium lithoaluminate; phosphor
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-23
      DOI: 10.1107/S2052520619016391
      Issue No: Vol. 76, No. 1 (2020)
       
  • Crystal engineering of an adenine–decavanadate molecular device towards
           label-free chemical sensing and biological screening

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      Authors: Sedghiniya; S., Soleimannejad, J., Jahani, Z., Davoodi, J., Janczak, J.
      Pages: 85 - 92
      Abstract: Due to the inherent geometrical interdependencies of nucleic acid structures, the ability to engineer biosensors that rely on the specific interactions of these compounds is of considerable importance. Additionally, sensing or screening in a label-free fashion is a capability of these structures that can be readily achieved by exploiting the fluorescent component. In this work, the [AdH]6[V10O28].4(H2O) (1) supramolecular structure is introduced using adenine and decavanadate moieties that allow probing of selectivity to specific nucleic acid binding events by optical changes. The structure of (1) is an alternating organic–inorganic hybrid architecture of cationic adeninium (AdH+) ribbons and anionic decavanadate (DV)–water sheets. The luminescent screening and anticancer activity of compound (1) on the two human mammary carcinoma cell lines MDA-MB-231 and MCF7 were investigated using fluorescent microscopy and MTT assays, respectively. It was found that compound (1) is cell permeable with no toxicity below 12.5 µM concentration and moderate cytotoxicity at concentrations as high as 200 µM in human breast cancer cell lines, making it a useful tool to study the cell nucleus in real time.
      Keywords: polyoxometalate; nucleic acid; decavanadate; adenine; label-free biosensor; MTT test; MDA-MB-231; MCF7; triple negative breast cancer
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-24
      DOI: 10.1107/S2052520619016196
      Issue No: Vol. 76, No. 1 (2020)
       
  • The incommensurately modulated structures of low-temperature labradorite
           feldspars: a single-crystal X-ray and neutron diffraction study

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      Authors: Jin; S., Xu, H., Wang, X., Jacobs, R., Morgan, D.
      Pages: 93 - 107
      Abstract: Labradorite feldspars of the plagioclase solid solution series have been known for their complicated subsolidus phase relations and enigmatic incommensurately modulated structures. Characterized by the irrationally indexed e-reflections in the diffraction pattern, e-labradorite shows the largest variation in the incommensurate ordering states among the e-plagioclase structures. The strongly ordered low-temperature e-labradorite is one of the last missing pieces of the e-plagioclase puzzle. Nine plutonic and metamorphic labradorite feldspar samples from Canada, Ukraine, Minnesota (USA), Tanzania and Greenland with compositions ranging from An52.5 to An68 were studied with single-crystal X-ray diffraction. Two crystals from Labrador, Canada, and Duluth, MN, USA, with wide enough twin lamellae were analyzed with single-crystal neutron diffraction. The incommensurately modulated structures of e-plagioclase are refined for the first time with neutron diffraction data, which confirmed that the T—O distance modulation in the low-temperature e-plagioclase results from the Al–Si ordering in the framework. Detailed configurations of the M site are also observed in the structures refined from neutron diffraction data, which were not possible to see with X-ray diffraction data. The relation between the q-vectors and the mole% An composition is revealed for the entire compositional range of e-plagioclase, from An25 to An75. The previously proposed two-trend relation depending on the cooling rate and phase transition path is confirmed. A new classification of e-plagioclase (eα, eβ and eγ) is proposed based on the q-vector of the structure, which makes it an independent character from the presence/absence of density modulation. New parameters are proposed to quantify the ordering states of these complicated aperiodic structures of e-plagioclases, such as the difference between 〈T1o—O〉 and 〈T1m—O〉 at phase t = 0.2 or the normalized intensity of the (071\bar 1) reflection.
      Keywords: labradorite; e-plagioclase; neutron diffraction; incommensurately modulated structure; density modulation
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-28
      DOI: 10.1107/S2052520619017128
      Issue No: Vol. 76, No. 1 (2020)
       
  • Structure of strontium tellurite glass, anti-glass and crystalline phases
           by high-energy X-ray diffraction, reverse Monte Carlo and Rietveld
           analysis

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      Authors: Kaur; R., Khanna, A., Hirdesh, , Dippel, A.-C., Gutowski, O., González, F., González-Barriuso, M.
      Pages: 108 - 121
      Abstract: The structures of xSrO–(100 − x)TeO2 (x = 5, 7.5, 8.5 and 10 mol.%) glass, anti-glass and crystalline samples were studied by high-energy X-ray diffraction (HEXRD), reverse Monte Carlo (RMC) simulations, atomic pair distribution function analysis and Fullprof Rietveld refinement. The atomic pair distributions show the first peak at 1.90 Å due to the Te—O equatorial bonds and the Te—O peak is asymmetrical due to the range of Te—O bond lengths in glass, anti-glass and crystalline samples. The short-range structural properties of glasses such as Te—O bond lengths, Te–O speciation, Te–Te distances and O—Te—O bond angle distributions were determined by RMC simulations. The average Te–O coordination number (NTe–O) for 5SrO–95TeO2 glass is 3.93 which decreases to 3.59 on increasing the SrO concentration to 10 mol.%. The changes in NTe–O revealed that the glass network predominantly contains TeO4 units with a small amount of TeO3 units and there is a structural transformation TeO4 → TeO3 with an increase in SrO concentration. The O—Te—O bond angle distributions have a peak at 79° and reveal that the Oequatorial—Te—Oequatorial bonds are the most abundant linkages in the tellurite network. Two glass samples containing 7.5 and 8.5 mol.% of SrO were annealed at 350°C for 1 h to produce anti-glass phases; they were further annealed at 450°C for 4 h to transform them into crystalline phases. The anti-glass samples are disordered cubic SrTe5O11 and the disordered monoclinic SrTeO3 phases, whereas the crystalline samples contain monoclinic SrTeO3 and the orthorhombic TeO2 phases. The unit-cell parameters of the anti-glass and crystalline structures were determined by Fullprof Rietveld refinement. Thermal studies found that the glass transition temperature increases with an increase in SrO mol.% and the results on the short-range structure of glasses from Raman spectroscopy are in agreement with the RMC findings.
      Keywords: tellurite glasses and anti-glasses; high-energy X-ray diffraction; reverse Monte Carlo simulations; Rietveld refinement
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-28
      DOI: 10.1107/S2052520620000025
      Issue No: Vol. 76, No. 1 (2020)
       
  • Supramolecular insight into the substitution of sulfur by selenium, based
           on crystal structures, quantum-chemical calculations and biosystem
           recognition

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      Authors: Đorđević; I.S., Popadić, M., Sarvan, M., Petković-Benazzouz, M., Janjić, G.V.
      Pages: 122 - 136
      Abstract: Statistical analysis of data from crystal structures extracted from the Cambridge Structural Database (CSD) has shown that S and Se atoms display a similar tendency towards specific types of interaction if they are part of a fragment that corresponds to the side chains of cysteine (Cys), methionine (Met) selenocysteine (Sec) and selenomethionine (Mse). The most numerous are structures with C—H...Se and C—H...S interactions (∼80%), notably less numerous are structures with Se...Se and S...S interactions (∼5%), and Se...π and S...π interactions are the least numerous. The results of quantum-chemical calculations have indicated that C—H...Se (∼−0.8 kcal mol−1) and C—H...S interactions are weaker than the most stable parallel interaction (∼−3.3 kcal mol−1) and electrostatic interactions of σ/π type (∼−2.6 kcal mol−1). Their significant presence can be explained by the abundance of CH groups compared with the numbers of Se and S atoms in the crystal structures, and also by the influence of substituents bonded to the Se or S atom that further reduce their possibilities for interacting with species from the environment. This can also offer an explanation as to why O—H...Se (∼−4.4 kcal mol−1) and N—H...Se interactions (∼−2.2 kcal mol−1) are less numerous. Docking studies revealed that S and Se rarely participate in interactions with the amino acid residues of target enzymes, mostly because those residues preferentially interact with the substituents bonded to Se and S. The differences between Se and S ligands in the number and positions of their binding sites are more pronounced if the substituents are polar and if there are more Se/S atoms in the ligand.
      Keywords: substitution of S by Se; supramolecular structure; Se...Se interactions; biosystem recognition
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-29
      DOI: 10.1107/S2052520619016287
      Issue No: Vol. 76, No. 1 (2020)
       
  • Low-temperature crystal structure of the unconventional spin-triplet
           superconductor UTe2 from single-crystal neutron diffraction

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      Authors: Hutanu; V., Deng, H., Ran, S., Fuhrman, W.T., Thoma, H., Butch, N.P.
      Pages: 137 - 143
      Abstract: The crystal structure of a new superconductor UTe2 has been investigated using single-crystal neutron diffraction for the first time at the low temperature (LT) of 2.7 K, just above the superconducting transition temperature of ∼1.6 K, in order to clarify whether the orthorhombic structure of type Immm (No. 71), reported for the room-temperature (RT) structure persists down to the superconducting phase and can be considered as a parent symmetry for the development of spin-triplet superconductivity. In contrast to the previously reported phase transition at about 100 K [Stöwe (1996). J. Solid State Chem. 127, 202–210], our high-precision LT neutron diffraction data show that the body-centred RT symmetry is indeed maintained down to 2.7 K. No sign of a structural change from RT down to 2.7 K was observed. The most significant change depending on temperature was observed for the U ion position and the U–U distance along the c direction, implying its potential importance as a magnetic interaction path. No magnetic order could be deduced from the neutron diffraction data refinement at 2.7 K, consistent with bulk magnetometry. Assuming normal thermal evolution of the lattice parameters, moderately large linear thermal expansion coefficients of about α = 2.8 (7) × 10−5 K−1 are estimated.
      Keywords: crystal structure; single-crystal neutron diffraction; phase transition; unconventional superconductivity; magnetic order; UTe2
      Citation: urn:issn:2052-5206
      PubDate: 2020-01-29
      DOI: 10.1107/S2052520619016950
      Issue No: Vol. 76, No. 1 (2020)
       
  • Revised radii of the univalent Cu, Ag, Au and Tl cations

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      Authors: Batsanov; S.S.
      Pages: 38 - 40
      Abstract: Radii of Cu+, Ag+, Au+ and Tl+ cations are determined by the additive method from interatomic distances in molecular and/or crystalline halides, oxides, chalcogenides and cyanides with different coordinations of atoms, and then recalculated for the 6-coordination number. The averaged (from 74 structures) values of revised radii are equal to r(Cu+) = 0.74 Å, r(Ag+) = 0.99 Å, r(Au+) = 0.92 Å, r(Tl+) = 1.22 Å, which are consistent with radii calculated from direct cation–cation contacts in ultimately compressed metals.
      Keywords: ionic radii; coordination numbers; univalent cations
      Citation: urn:issn:2052-5206
      PubDate: 2019-12-19
      DOI: 10.1107/S2052520619015531
      Issue No: Vol. 76, No. 1 (2019)
       
 
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