ORCID Profile
0000-0002-7708-5597
Current Organisation
The University of Edinburgh
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Publisher: International Union of Crystallography (IUCr)
Date: 2020
DOI: 10.1107/S2052252519016105
Abstract: 3D electron diffraction (3DED) has been used to follow polymorph evolution in the crystallization of glycine from aqueous solution. The three polymorphs of glycine which exist under ambient conditions follow the stability order β α γ. The least stable β polymorph forms within the first 3 min, but this begins to yield the α-form after only 1 min more. Both structures could be determined from continuous rotation electron diffraction data collected in less than 20 s on crystals of thickness ∼100 nm. Even though the γ-form is thermodynamically the most stable polymorph, kinetics favour the α-form, which dominates after prolonged standing. In the same s le, some β and one crystallite of the γ polymorph were also observed.
Publisher: Wiley
Date: 30-07-2018
Abstract: Elastically flexible crystals form an emerging class of materials that exhibit a range of notable properties. The mechanism of thermal expansion in flexible crystals of bis(acetylacetonato)copper(II) is compared with the mechanism of molecular motion induced by bending and it is demonstrated that the two mechanisms are distinct. Upon bending, in idual molecules within the crystal structure reversibly rotate, while thermal expansion results predominantly in an increase in intermolecular separations with only minor changes to molecular orientation through rotation.
Publisher: International Union of Crystallography (IUCr)
Date: 16-09-2021
DOI: 10.1107/S205252062100740X
Abstract: The crystal structure of the monoclinic polymorph of the primary amino acid L-histidine has been determined for the first time by single-crystal neutron diffraction, while that of the orthorhombic polymorph has been reinvestigated with an untwinned crystal, improving the experimental precision and accuracy. For each polymorph, neutron diffraction data were collected at 5, 105 and 295 K. Single-crystal X-ray diffraction experiments were also performed at the same temperatures. The two polymorphs, whose crystal packing is interpreted by intermolecular interaction energies calculated using the Pixel method, show differences in the energy and geometry of the hydrogen bond formed along the c direction. Taking advantage of the X-ray diffraction data collected at 5 K, the precision and accuracy of the new Hirshfeld atom refinement method implemented in NoSpherA2 were probed choosing various settings of the functionals and basis sets, together with the use of explicit clusters of molecules and enhanced rigid-body restraints for H atoms. Equivalent atomic coordinates and anisotropic displacement parameters were compared and found to agree well with those obtained from the corresponding neutron structural models.
Publisher: International Union of Crystallography (IUCr)
Date: 20-11-2022
DOI: 10.1107/S2052252521010708
Abstract: Single-crystal X-ray and neutron diffraction data are usually collected using separate s les. This is a disadvantage when the s le is studied at high pressure because it is very difficult to achieve exactly the same pressure in two separate experiments, especially if the neutron data are collected using Laue methods where precise absolute values of the unit-cell dimensions cannot be measured to check how close the pressures are. In this study, diffraction data have been collected under the same conditions on the same s le of copper(II) sulfate pentahydrate, using a conventional laboratory diffractometer and source for the X-ray measurements and the Koala single-crystal Laue diffractometer at the ANSTO facility for the neutron measurements. The s le, of dimensions 0.40 × 0.22 × 0.20 mm 3 and held at a pressure of 0.71 GPa, was contained in a miniature Merrill–Bassett diamond-anvil cell. The highly penetrating diffracted neutron beams passing through the metal body of the miniature cell as well as through the diamonds yielded data suitable for structure refinement, and compensated for the low completeness of the X-ray measurements, which was only 24% on account of the triclinic symmetry of the s le and the shading of reciprocal space by the cell. The two data-sets were combined in a single `XN' structure refinement in which all atoms, including H atoms, were refined with anisotropic displacement parameters. The precision of the structural parameters was improved by a factor of up to 50% in the XN refinement compared with refinements using the X-ray or neutron data separately.
Publisher: International Union of Crystallography (IUCr)
Date: 30-10-2021
DOI: 10.1107/S2052252521010101
Abstract: Time-resolved carbamazepine crystallization from wet ethanol has been monitored using a combination of cryoTEM and 3D electron diffraction. Carbamazepine is shown to crystallize exclusively as a dihydrate after 180 s. When the timescale was reduced to 30 s, three further polymorphs could be identified. At 20 s, the development of early stage carbamazepine dihydrate was observed through phase separation. This work reveals two possible crystallization pathways present in this active pharmaceutical ingredient.
Publisher: American Chemical Society (ACS)
Date: 21-12-2022
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7SC04460G
Abstract: The synergistic combination of high pressure techniques with ab initio methods creates a powerful tool to understand giant magnetic anisotropy.
Publisher: American Chemical Society (ACS)
Date: 06-11-2020
Publisher: International Union of Crystallography (IUCr)
Date: 02-08-2017
DOI: 10.1107/S2052520617006412
Abstract: 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 Fe 3+ . First-principles calculations and the presence of short Cl...Cl contacts for Ga 3+ suggest the [GaCl 4 ] − anion to be conformationally hindered due to stronger lone-pair–σ-hole interactions. The conformationally more flexible Fe 3+ structures show sublattice melting with the onset of rotational disorder in the [NMe 4 ] + cations occurring 40 K below the corresponding onset of rotational disorder in the [FeCl 4 ] − sublattice.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Simon Parsons.