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ISSN: 2052-5206

June 2014 issue

Special issue on Non-ambient Crystallography

Guest Editors: David G. Billing and Andrzej Katrusiak

Highlighted illustration

Cover illustration: Isothermal and isochoric crystallization can be used for growing high-quality single crystals of compounds which are liquids or unstable at normal conditions. The cover illustrates the differences in melting and boiling points of dibromobenzene isomers (top) and shows a single crystal of highly hygroscopic pyridine N-oxide (bottom), with a chip of ruby on its side used for pressure calibration, all inside the chamber of a diamond-anvil cell. For details see Patyk et al. [(2014), Acta Cryst. B70, 487-491] and Dziubek & Katrusiak [(2014), Acta Cryst. B70, 492-497].

editorial


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Non-ambient conditions are used with increasing regularity in structural studies of crystals and functional materials – this editorial summarizes very briefly the history of environment devices and describes selected recent achievements in this field.

scientific commentaries


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Framework and applications of a new approach, developed by Degtyareva to analyze the stability of non-close-packed structures of elemental metals in the context of Hume–Rothery rules and Fermi sphere–Brillouin zone interactions, are discussed.

Acta Cryst. (2014). B70, 403
doi: 10.1107/S2052520614011652
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In situ structural analyses of gas-loaded crystals represent a rapidly growing field of study both in the home laboratory and at large central facilities, offering unique insights into the location of binding sites, the nature of the host–guest interactions and the effects of gas loading on the host frameworks.

feature articles


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Adsorption and separation of gases is one of the primary applications of the class of materials known as metal–organic frameworks (MOFs). The role of crystallography in characterizing adsorbed gas molecules and changes in framework structure upon gas sorption is reviewed.

non-ambient crystallography


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Transition of Ca under pressure from close-packed structures face-centred cubic (f.c.c.) and base-centred cubic (b.c.c.) to the open-packed simple cubic structure is explained by a core electron overlap with the valence band. Ca-VII and In5Bi3 exhibit similar crystal structures due to common features of their electronic structure.

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Phase diagrams of the elements and equations of state for a wide range of pressures and temperatures are presented with innovative artwork for better visualization.

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The spin-crossover behaviour under applied pressure of {Fe(pmd)2[Ag(CN)2]2}n (pmd = pyrimidine) has been investigated from the structural point of view by means of neutron Laue diffraction, and the results correlated with those of magnetic measurements to describe the pressure–temperature phase diagram of this compound.

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The paper reviews the results of recent studies on the high-pressure behavior of microporous materials with MFI framework type, based on in situ experiments performed with both penetrating and non-penetrating pressure-transmitting media. Different high-pressure-induced phenomena and deformation mechanisms (e.g. pressure-induced over-hydration, pressure-induced amorphization) and the influence of framework and extra-framework composition, and of the presence of silanol defects on the response to high pressure of MDI-type zeolites are discussed.

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Rietveld refinements of high-pressure synchrotron powder X-ray diffraction measurements of lanthanum ferrite (LaFeO3) reveal two phase transitions (second and first order) on the room-temperature isotherm up to a pressure of 48 GPa. Equations of state were used to determine the bulk modulus of B0 = 172 GPa and the corresponding pressure derivative of B0 = 4.3.

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The high-pressure structural behaviour of ThX compounds has been studied by ab-initio calculations using the linear muffin-tin orbital method with the generalized gradient approximation. The results are compared with experiments.

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The behaviour under compression of a series of six isomorphous coordination complexes [MX2(1,4,7-trithiacyclononane)] (M = Pd, Pt; X = Cl, Br, I) is reported. The different structural properties of these complexes are described and analysed, including by the use of density functional theory (DFT) and bond-order calculations.

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An oil-like aqueous solution of highly hygroscopic pyridine N-oxide (PNO) has been compressed in a diamond–anvil cell and single crystals of PNO have been grown under isothermal and isochoric conditions. The PNO anhydrate ambient-pressure structure is stabilized by CH⋯O contacts up to 2 GPa at least.

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The crystal structures of three isomeric dibromobenzenes have been inspected and the relations between the short intermolecular Br⋯Br contacts, and characteristic bulk properties discussed. The ortho and meta isomers have been crystallized under low-temperature and high-pressure conditions.

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It is well known that pre-treatment procedures affect catalyst performance. In situ X-ray diffraction was used in this study to monitor the changes in phase composition and crystallite size during the pre-treatment of Fe/TiO2 catalysts, yielding insight into crystalline and non-crystalline phase changes and metal–support interactions.

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Layered α-Zr(HPO4)2·H2O has been studied under hydrostatic and non-hydrostatic pressures up to 10 GPa using synchrotron X-ray powder diffraction techniques. There is no evidence for pressure-induced hydration with the main structural changes due to flexibility in the angles about the O atoms linking the zirconium and phosphorus polyhedra.

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Phase transitions with fragmentation of the single crystals into fine powder were observed for partially methylated N-methyl and N,N-dimethylglycine, whereas the structural changes in N,N,N-trimethylglycine were continuous with some peculiar features in the 1.4–2.0 GPa pressure range, and accompanied by splitting of the crystals into several large fragments. Structural rearrangements in N-methylglycine and N,N,N-trimethylglycine were strongly dependent on the rate of pressure variation: the higher the rate of increasing pressure, the lower the pressure at which the phase transition occurred.


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The phase transitions of Zn2P2O7 were analyzed by differential scanning calorimetry and high-temperature single-crystal and powder X-ray diffraction.

research papers


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A structural model has been developed to interpret the non-Bragg diffraction features that occur during the dehydration of an active pharmaceutical ingredient (API) hydrate crystal.

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The charge-density distribution of pyrazinamide reveals the nature of its chemical bonding. The electrostatic potential surface of the molecule predicts the locations of strong interactions.

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Current research was performed with the purpose of solving the structure of a new ordered phase revealed in the quasi-binary UAl3–USi3 system. The final atomic model derived from a combination of electron and powder X-ray diffraction data could be explained by theoretical crystallography through a Bärnighausen tree, using the UAl3 structure as an aristotype.

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The structure of β-cyclodextrin dimethylformamide 12.5 hydrate has been determined. The main factors responsible for the packing differences and similarities in related complexes have been investigated by a thorough structural analysis.

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The response of a negatively charged metal–organic framework to temperature has been studied in detail with multi-temperature single-crystal X-ray diffraction.

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A series of linear alkaline earth coordination polymers incorporating diphenylphosphinate ligands are reported. The compounds have been characterized by single-crystal X-ray diffraction and 1H NMR and FT–IR spectroscopy.

short communications


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The oxidation-state independent `bond valence (s) versus bond length (r)' correlation curve for manganese–oxygen bonds has been closely approximated using the two-parameter s = f(r) function s = [(r0l)/(rl)]2, where r0 = 1.763 (2) Å and l = 1.148 (9) Å.

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Density functional lattice dynamical calculations uncover the key role played by A-site elements with (n − 1)d10ns0 valence configurations (n = 5 and 6) in controlling the hexagonal-to-triclinic transformation in fluorapatites. The uniqueness of this site occupancy and chemistry was previously detected by data-driven methods, and the present study provides an electronic structure-based explanation of the prior informatics findings.
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