Browsing by Author "Lemée-Cailleau, MH"

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    4-phenoxyphenol: a porous molecular material
    (American Chemical Society, 2012-04-01) Thomas, LH; Cheung, E; Jones, AOF; Kallay, AA; Lemée-Cailleau, MH; McIntyre, GJ; Wilson, CC
    4-Phenoxyphenol is a simple organic molecule that crystallizes as a porous material with channels running throughout the structure. The channels are constructed by a 6-fold hydrogen bonded ring and can host solvent molecules incorporated during crystal growth, with a minimum channel diameter of 5.8-5.9 angstrom; each channel usually contains a single solvent molecule per unit cell. The hydrogen bonded ring shows surprising flexibility, being able both to breathe and to sustain its crystalline integrity even when grown with empty pores. This is particularly surprising given that the remainder of the interactions within the crystal structure are C-H center dot center dot center dot pi interactions and are weak in nature. It is also possible to grow "dry" porous 4-phenoxyphenol crystals by using a bulky solvent in the recrystallization. © 2012, American Chemical Society.
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    Insights into the crystallisation process from anhydrous, hydrated and solvated crystal forms of diatrizoic acid
    (Wiley, 2014-11-04) Fucke, K; McIntyre, GJ; Lemée-Cailleau, MH; Wilkinson, C; Edwards, AJ; Howard, JAK; Steed, JW
    Diatrizoic acid (DTA), a clinically used X-ray contrast agent, crystallises in two hydrated, three anhydrous and nine solvated solid forms, all of which have been characterised by X-ray crystallography. Single-crystal neutron structures of DTA dihydrate and monosodium DTA tetrahydrate have been determined. All of the solid-state structures have been analysed using partial atomic charges and hardness algorithm (PACHA) calculations. Even though in general all DTA crystal forms reveal similar intermolecular interactions, the overall crystal packing differs considerably from form to form. The water of the dihydrate is encapsulated between a pair of host molecules, which calculations reveal to be an extraordinarily stable motif. DTA presents functionalities that enable hydrogen and halogen bonding, and whilst an extended hydrogen-bonding network is realised in all crystal forms, halogen bonding is not present in the hydrated crystal forms. This is due to the formation of a hydrogen-bonding network based on individual enclosed water squares, which is not amenable to the concomitant formation of halogen bonds. The main interaction in the solvates involves the carboxylic acid, which corroborates the hypothesis that this strong interaction is the last one to be broken during the crystal desolvation and nucleation process.© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Neutron Laue and X-ray diffraction study of a new crystallographic superspace phase in n-nonadecane-urea
    (International Union of Crystallography, 2015-01) Zerdane, S; Mariette, C; McIntyre, GJ; Lemée-Cailleau, MH; Rabiller, P; Guérin, L; Ameline, JC; Toudic, B
    Aperiodic composite crystals present long-range order without translational symmetry. These materials may be described as the intersection in three dimensions of a crystal which is periodic in a higher-dimensional space. In such materials, symmetry breaking must be described as structural changes within these crystallographic superspaces. The increase in the number of superspace groups with the increase in the dimension of the superspace allows many more structural solutions. This is illustrated in n-nonadecane-urea, revealing a fifth higher-dimensional phase at low temperature. © International Union of Crystallography
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    Reduction of a chelating bis(NHC) palladium(II) complex to [{μbis( NHC)}2Pd2H]+: a terminal hydride in a binuclear palladium(I) species formed under catalytically relevant conditions
    (Wiley-VCH Verlag Berlin, 2010-08-23) Boyd, PDW; Edwards, AJ; Gardiner, MG; Ho, CC; Lemée-Cailleau, MH; McGuinness, DS; Riapanitra, A; Steed, JW; Stringer, DN; Yates, BF
    The first palladium(I) N-heterocyclic carbene complex has been isolated in high yield by the base-assisted reduction of a palladium(II) precursor. The location of the unique terminal hydride (see picture; PdI cyan, H white, N blue) was established by neutron crystal structure determination, and the solution fluxional behavior of the complex was explored. © 2010, Wiley-VCH Verlag Berlin
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    Surveying the higher dimensions of the aperiodic composite nonadecane/urea
    (Australian Institute of Physics, 2020-02-04) McIntyre, GJ; Lemée-Cailleau, MH; Toudic, B
    A decade ago, few we observed for the first time that there exist phase transitions where the structural changes correspond just to degrees of freedom hidden in the internal (super)space of an aperiodic material, here the composite nonadecane/urea [1]. A key factor in the discovery of this type of transition [2] was the examination of the diffraction pattern in 3D, only possible at the time on a four-circle triple-axis neutron spectrometer, the analyzer used in zero-energy transfer to reduce the background and improve resolution. Despite the greater accessibility in reciprocal space compared with earlier experiments using a conventional triple-axis spectrometer, the weak intensity of the superlattice reflections limited the volume of reciprocal space that could be explored. Modern neutron Laue diffractometers with large image-plate detectors permit rapid and extensive exploration of reciprocal space with high resolution in the two-dimensional projection and a wide dynamic range with negligible bleeding of intense diffraction spots [3]. Surveying nonadecane/urea with neutron Laue diffraction from 300 K to 4 K revealed further detail of the superspace-driven phase transition, notably an increase in misorientation in the plane perpendicular to the composite misfit axis, as well as a first-order transition to a new phase at lower temperature. Complementary monochromatic X-ray examination, again using a high-resolution image-plate detector, showed that this new phase corresponds to additional commensurate ordering of the guest alkane subsystem. These observations shed light on how nature can use the degrees of freedom hidden in the internal superspace to form states that cannot be envisaged in the usual 3D real space.
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    Temperature dependent solid-state proton migration in dimethylurea-oxalic acid complexes
    (Royal Society of Chemistry, 2012-01-01) Jones, AOF; Lemée-Cailleau, MH; Martins, DMS; McIntyre, GJ; Oswald, IDH; Pulham, CR; Spanswick, CK; Thomas, LH; Wilson, CC
    The phenomenon of solid-state proton migration within molecular complexes containing short hydrogen bonds is investigated in two dimethylurea-oxalic acid complexes. Extensive characterisation by both X-ray and neutron diffraction shows that proton migration along the hydrogen bond can be induced in these complexes as a function of temperature. This emphasises the subtle features of the hydrogen bond potential well in such short hydrogen bonded complexes, both intrinsically and in the effect of the local crystalline environment. Based on these findings, the synthesis and analysis of a series of solid-state molecular complexes is shown to be a potential route to designing materials with tuneable proton migration effects. © 2012, Royal Society of Chemistry.