Browsing by Author "Binns, J"

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    Accurate hydrogen parameters for the amino acid L-leucine
    (International Union of Crystallography, 2016-01) Binns, J; Parsons, S; McIntyre, GJ
    The structure of the primary amino acid L-leucine has been determined for the first time by neutron diffraction. This was made possible by the use of modern neutron Laue diffraction to overcome the previously prohibitive effects of crystal size and quality. The packing of the structure into hydrophobic and hydrophilic layers is explained by the intermolecular interaction energies calculated using the PIXEL method. Variable-temperature data collections confirmed the absence of phase transitions between 120 and 300 K in the single-crystal form. © International Union of Crystallography
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    Crystal structure of protic ionic liquids and their hydrates
    (International Union of Crystallography, 2021-08-14) Hassett, MP; Brand, HEA; Binns, J; Martin, AV; Greaves, TL
    Protic Ionic Liquids (PILs) are a class of tailorable solvents made up of fused salts with melting points below 100 °C, which are formed through a Brønsted acid-base reaction involving proton exchange[1]. These solvents have applications as lubricants, electrolytes, and many other uses[2]. Although they are quite similar to molten salts, their crystal structures have not been explored in-depth, with only ethylammonium nitrate (EAN) having a reported crystal structure[3, 4]. Ten alkylammonium-based protic ionic liquids at both neat (<1 wt% water) and 90 mol% PIL, 10 mol% water concentrations were selected. Diffraction patterns were collected at the Australian Synchrotron ANSTO while attempting to crystallise the samples by cooling to 120 K. Five samples crystallised (3 neat, 2 dilute), where the temperature of the system was then increased at a rate of 6 K/min to room temperature. From these patterns we have identified a number of crystal phases, identifying their stability ranges and lattice constant variation from 120 K to room temperature. © 2021 The Authors
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    Development of high-pressure single-crystal neutron diffraction on the Laue diffractometer, KOALA, at OPAL
    (Australian Institute of Physics, 2016-02-04) Binns, J; McIntyre, GJ; Kamenev, KV; Moggach, S; Parsons, S
    Hydrogen bonds are one of the most important classes of intermolecular interaction, and accurate H-atom positions are critical for analysis of the energy terms which determine the thermodynamic stability of molecular crystals. At ambient pressure and low temperatures, H atoms can often be located by X-ray diffraction, and X-ray data can provide an accurate picture of the intermolecular contacts. High-pressure experiments do not afford this luxury. The high systematic errors introduced by the pressure cell and low completeness mean that H-atom positions are not revealed in X-ray Fourier maps. In some compounds H-atom positions can be inferred from the positions of other atoms, but this is not possible in all cases. Neutron diffraction data are much more sensitive to H than are X-ray data, and they are essential in cases where accurate H-atom location is important. Neutron powder patterns of complex molecular systems suffer from extensive peak overlap, and single-crystal diffraction therefore has a huge advantage; there is also no need to deuterate. The main disadvantage of neutron diffraction is that a large sample is usually required, which is at odds with the decreasing volumes possible with increasing pressure with existing pressure-cell materials. Modern neutron Laue diffraction and large moissanite anvil cells offer some respite 1, but complementing high-pressure X-ray data with high-pressure neutron data is still fraught with technical challenges to obtain identical conditions. Initial developmental experiments using a miniature diamond-anvil cell with a single crystal of size typical for X-ray diffraction on the KOALA Laue diffractometer at OPAL have shown the feasibility of the Laue technique for single-crystal neutron studies at high pressure. Remarkably, data completeness is similar to ambient-pressure measurements, despite the presence of the pressure cell. It is now possible to perform joint X-ray and neutron studies on the same sample under identical conditions.
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    High-pressure single-crystal neutron diffraction
    (Australian Institute of Nuclear Science and Engineering, 2016-11-29) McIntyre, GJ; Binns, J; Parsons, S
    High-pressure neutron diffraction is always challenging, but it can offer several advantages over high-pressure X-ray diffraction to make meeting those challenges worthwhile. In addition to the usual higher sensitivity to low-X elements, notably hydrogen, and to magnetic moments, the low absorption by many pressure cell materials can yield greater reciprocal space coverage for single crystals. The low scattering power usually requires considerably larger sample volumes than with X-rays, but for the same reason the cell-wall materials can be quite thick. Common cell designs include He-gas cells and simple clamp cells, opposed piston cells (e.g. Bloch, McWhan), opposed-anvil cells (e.g. diamond anvil cell, Paris-Edinburgh cell), and multi-anvil cells, each adapted to sample volume, accessibility, pressure, and other external parameters, especially temperature, that suit the scientific question of interest. State-of-the art experiments using each cell type will be described. A special challenge in high-pressure diffraction is to perform neutron and X-ray experiments on the same material under the same conditions. Previously, this meant using different cells and samples with achieving identical pressures a hit-or-miss affair. This has all changed with the recent demonstration on KOALA on the OPAL research reactor that modern neutron Laue diffraction can be performed on the same sample in the same diamond-anvil cell as used for laboratory X-ray experiments [1].
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    High-pressure single-crystal neutron diffraction
    (Australian Institute of Physics, 2017-02-03) McIntyre, GJ; Binns, J; Parsons, S
    High-pressure neutron diffraction is always challenging, but it can offer several advantages over high-pressure X-ray diffraction to make meeting those challenges worthwhile. In addition to the usual higher sensitivity to low-X elements, notably hydrogen, and to magnetic moments, the low absorption by many pressure cell materials can yield greater reciprocal space coverage for single crystals. The low scattering power usually requires considerably larger sample volumes than with X-rays, but for the same reason the cell-wall materials can be quite thick. Common cell designs include He-gas cells and simple clamp cells, opposed piston cells (e.g. Bloch, McWhan), opposed-anvil cells (e.g. diamond anvil cell, Paris-Edinburgh cell), and multi-anvil cells, each adapted to sample volume, accessibility, pressure, and other external parameters, especially temperature, that suit the scientific question of interest. State-of-the-art experiments using each cell type will be described. A special challenge in high-pressure diffraction is to perform neutron and X-ray experiments on the same material under the same conditions. Previously, this meant using different cells and samples with achieving identical pressures largely a hit-or-miss affair. This has all changed with the recent demonstration on KOALA on the OPAL research reactor that modern neutron Laue diffraction can be performed on the same sample in the same diamond-anvil cell as used for laboratory X-ray experiments [1].
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    Multiple scattering in neutron Laue diffraction
    (Australian Institute of Nuclear Science and Engineering, 2018-11-19) McIntyre, GJ; Maynard-Casely, HE; Binns, J
    Apart from the specialised but important application to phase determination, multiple scattering in single-crystal neutron diffraction is usually an undesirable source of error. The presence of multiple scattering for a particular Bragg reflection can be verified by performing an azimuthal scan, if the diffractometer offers that possibility, or by varying the wavelength. Either of these checks is generally straightforward on a monochromatic diffractometer, where attention can be easily focused on a single reflection. Correction for multiple scattering ranges from rejection of the reflections affected in longer-wavelength experiments to subtraction of an empirically determined constant contribution from all data in shorter-wavelength experiments. Little consideration has thus far been given to the contribution of multiple scattering to neutron Laue diffraction, due primarily to multiple scattering being less likely to occur in the samples best adapted to the technique. In addition,scanning a single reflection to detect the presence of multiple scattering is not the forte of Laue diffraction where many reflections are excited and detected simultaneously, and the broad waveband further complicates the possibility to correct for multiple scattering. Here we show that the multiple scattering can occur in a neutron Laue experiment by using two single crystals (in a diamond-anvil high-pressure cell) to highlight the effect in the Laue pattern. The (few) observations in this unconventional experiment allow estimation of the magnitude of the effect in standard neutron Laue experiments both at reactor and spallation sources.
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    Neutron and high-pressure X-ray diffraction study of hydrogen-bonded ferroelectric rubidium hydrogen sulfate
    (International Union of Crystallography, 2016-01-01) Binns, J; McIntyre, GJ; Parsons, S
    The pressure- and temperature-dependent phase transitions in the ferroelectric material rubidium hydrogen sulfate (RbHSO4) are investigated by a combination of neutron Laue diffraction and high-pressure X-ray diffraction. The observation of disordered O-atom positions in the hydrogen sulfate anions is in agreement with previous spectroscopic measurements in the literature. Contrary to the mechanism observed in other hydrogen-bonded ferroelectric materials, H-atom positions are well defined and ordered in the paraelectric phase. Under applied pressure RbHSO4 undergoes a ferroelectric transition before transforming to a third, high-pressure phase. The symmetry of this phase is revised to the centrosymmetric space group P21/c, resulting in the suppression of ferroelectricity at high pressure. © International Union of Crystallography
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    A non-topological mechanism for negative linear compressibility
    (Royal Society of Chemistry, 2016-05-13) Binns, J; Kamenev, KV; Marriott, KER; McIntyre, GJ; Moggach, SA; Murrie, M; Parsons, S
    Negative linear compressibility (NLC), the increase in a unit cell length with pressure, is a rare phenomenon in which hydrostatic compression of a structure promotes expansion along one dimension. It is usually a consequence of crystal structure topology. We show that the source of NLC in the Co(II) citrate metal–organic framework UTSA-16 lies not in framework topology, but in the relative torsional flexibility of Co(II)-centred tetrahedra compared to more rigid octahedra.© Open Access CC BY Licence - The Royal Society of Chemistry 2016
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    Phase transition sequences in tetra­methyl­ammonium tetra­chloro­metallates by x-ray diffraction and spectroscopic measurements
    (International Union of Crystallography, 2017-01) Binns, J; McIntyre, GJ; Barreda-Argüeso, JA; González, J; Aguado, F; Rodríguez, F; Valiente, R; Parsons, S
    The phase transition sequences of two members of the tetra­methyl­ammonium tetra­chloro­metallate(III) family of hybrid organic–inorganic salts have been determined and structurally characterized as a function of temperature for the first time. Unusually, a reduction in point-group symmetry with increasing temperature until reaching a cubic prototype phase is observed. Two additional intermediate phases are observed for Fe3+. First-principles calculations and the presence of short Cl...Cl contacts for Ga3+ suggest the [GaCl4]− anion to be conformationally hindered due to stronger lone-pair–σ-hole interactions. The conformationally more flexible Fe3+ structures show sublattice melting with the onset of rotational disorder in the [NMe4]+ cations occurring 40 K below the corresponding onset of rotational disorder in the [FeCl4]− sublattice. © International Union of Crystallography
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    Structural studies of phase transitions in hybrid organic-inorganic salts with temperature and pressure
    (Australian Institute of Physics, 2014-02-04) Binns, J; Parsons, S; Moggach, S; Valiente, R; McIntyre, GJ; Kamenev, KV
    The alkylammonium tetrachlorometallates have attracted significant attention for the numerous phase transitions observed in a relatively narrow range of temperatures and pressures as well as ferroelectric,-elastic and -magnetic behaviours. [1,2] Such simple organic salts could find possible applications as thin-film functional materials in low cost ferroelectric capacitors and RAM. With the exception of bis(tetramethylammonium) tetrachlorozincate(II) this class of materials has been subject to relatively little structural investigation, with a number of general phase sequences being determined from calorimetric and polarisation measurements. [3,4] While there are known to be ferroelectric phase transitions in many of these materials, the exact mechanism by which these simple organic salts exhibit such behaviour is unknown. We report on the phase sequences observed in two related materials: tetramethylammonium tetrachloroferrate(III) (TCF), and the previously unknown tetramethylammonium tetrachlorogallate(III) (TCG) which display re-entrant as well as plastic crystalline phases.
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    Towards joint high-pressure x-ray and neutron single-crystal diffraction
    (International Union of Crystallography, 2017-01) McIntyre, GJ; Binns, J; Kamenev, KV; Moggach, S; Parsons, S
    Diffraction methods can provide the highest-quality structural information about a crystal on the atomic scale and much work has been carried out to adapt X-ray and neutron diffraction techniques to a variety of challenging sample environments, including high-pressure. The ability to influence directly intermolecular distances makes high pressure one of the most important tools at our disposal for answering one of the big questions in chemistry - the prediction and control of solid-state structure. Modern neutron Laue diffractometers with large image-plate detectors permit extensive continuous sampling of reciprocal space with high resolution in the two-dimensional projection and a wide dynamic range with negligible bleeding of intense diffraction spots, qualities that are highly suited to high-pressure crystallography [1]. Here we show that high-pressure single-crystal neutron diffraction data can be collected using Laue diffraction from a sample of hexamine in a miniature diamond-anvil cell (mini-DAC) with no significant reductions in completeness or resolution [2]. The data are of similar quality, as judged by R-factors, geometric parameters, and estimated standard deviations, to those obtained at ambient pressures. This is achieved by the ability to measure diffracted intensity directly through the body of the mini-DAC. Joint high-pressure experiments using both X-ray and neutron diffraction on the same sample are now feasible using the mini-DAC and modern neutron Laue diffractometers like KOALA on the OPAL reactor. © International Union of Crystallography
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    Understanding order and correlation in liquid crystals by fluctuation scattering
    (Australian Nuclear Science and Technology Organisation, 2021-11-26) Binns, J; Adams, P; Kewish, CM; Greaves, TL; Martin, AV
    Characterising the supramolecular organisation of macromolecules in the presence of varying degrees of disorder remains one of the challenges of macromolecular research. Discotic liquid crystals (DLCs) are an ideal model system for understanding the role of disorder on multiple length scales. Consisting of rigid aromatic cores with flexible alkyl fringes, they can be considered as one-dimensional fluids along the stacking direction and they have attracted attention as molecular wires in organic electronic components and photovoltaic devices. With its roots in single-particle imaging, fluctuation x-ray scattering (FXS) is a method that breaks free of the requirement for periodic order. However, the interpretation of FXS data has been limited by difficulties in analysing intensity correlations in reciprocal space. Recent work has shown that these correlations can be translated into a three-and four-body distribution in real space called the pair-angle distribution function (PADF) – an extension of the familiar pair distribution function into a three-dimensional volume. The analytical power of this technique has already been demonstrated in studies of disordered porous carbons and self-assembled lipid phases. Here we report on the investigation of order-disorder transitions in liquid crystal materials utilising the PADF technique and the development of facilities for FXS measurements at the Australian Synchrotron. © 2021 The Authors
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    Use of a miniature diamond-anvil cell in high-pressure single-crystal neutron Laue diffraction
    (International Union of Crystallography, 2016-05) Binns, J; Kamenev, KV; McIntyre, GJ; Moggach, SA; Parsons, S
    The first high-pressure neutron diffraction study in a miniature diamond-anvil cell of a single crystal of size typical for X-ray diffraction is reported. This is made possible by modern Laue diffraction using a large solid-angle image-plate detector. An unexpected finding is that even reflections whose diffracted beams pass through the cell body are reliably observed, albeit with some attenuation. The cell body does limit the range of usable incident angles, but the crystallographic completeness for a high-symmetry unit cell is only slightly less than for a data collection without the cell. Data collections for two sizes of hexamine single crystals, with and without the pressure cell, and at 300 and 150 K, show that sample size and temperature are the most important factors that influence data quality. Despite the smaller crystal size and dominant parasitic scattering from the diamond-anvil cell, the data collected allow a full anisotropic refinement of hexamine with bond lengths and angles that agree with literature data within experimental error. This technique is shown to be suitable for low-symmetry crystals, and in these cases the transmission of diffracted beams through the cell body results in much higher completeness values than are possible with X-rays. The way is now open for joint X-ray and neutron studies on the same sample under identical conditions. © International Union of Crystallography - Open Access