Browsing by Author "Jones, AOF"

Now showing 1 - 6 of 6
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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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    The effect of local crystalline environment on hydrogen atom behavior in molecular complexes of a proton sponge
    (American Chemical Society, 2016-03-07) Jones, AOF; Kallay, AA; Lloyd, H; McIntyre, GJ; Wilson, CC; Thomas, LH
    Proton behavior within the hydrogen bond (HB) networks of five molecular complexes of the proton sponge DMAN and different organic acids is investigated by single-crystal neutron diffraction. The complexes form with either 2:1 (acid:DMAN) or 1:1 stoichiometric ratios and contain common structural motifs. All show proton transfer from an acid to DMAN, forming a DMANH+ moiety and hydrogen-bonded acid dimers; complexes with halobenzoic acids have acid molecules linked by short, strong, charge-assisted HBs, while all complexes contain a short, strong, intramolecular N–H···N HB in DMANH+. The hydrogen atom behavior within the short, strong HBs, accurately described from the neutron data, is rationalized in terms of weak interactions in the local crystal environment, with the position of the proton within both sets of short, strong HBs affected by a combination of the weak interactions in the vicinity of the HBs. A correlation is also found between the thermal motion of the bound proton in the N–H···N HB of DMANH+ and nearby oxygen atoms when they are sufficiently close to one another. This work shows that all interactions in the local environment combine to determine the behavior of protons within short, strong HBs and that, by taking these interactions into account, further control over the crystal structure and properties may be achievable. © 2016 American Chemical Society
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    Engineering short, strong hydrogen bonds in urea di-carboxylic acid complexes
    (Royal Society of Chemistry, 2014-04-17) Jones, AOF; Leech, CK; McIntyre, GJ; Wilson, CC; Thomas, LH
    A series of seven 2:1 molecular complexes of urea (U) and methyl ureas with di-carboxylic acids (A) are reported, along with the results of their study by variable temperature diffraction. These all contain short, strong O–H⋯O hydrogen bonds and a recurring acid⋯amide heterodimer forming U–A–U synthons. Despite differences in the degree of saturation of the linking C–C groups of the di-carboxylic acids and the single or double methyl substitution of one of the N atoms of the urea, the packing arrangements are remarkably similar in five of the complexes; the exceptions being N-methylurea oxalic acid and N,N-dimethylurea fumaric acid. The five similar molecular complexes all show contraction of one unit cell parameter on increasing temperature due to rearrangements of the weaker interactions which hold together the U–A–U units. The strength of the short, strong O–H⋯O hydrogen bond is shown to be linked both to the length of the connecting bridge between the carboxylic acid groups of the acid, and to the ΔpKa values between the two components. ©, 2014, The Royal Society of Chemistry.
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    Engineering short, strong, charge-assisted hydrogen bonds in benzoic acid dimers through cocrystallization with proton sponge
    (American Chemical Society, 2016-03-07) Thomas, LH; Jones, AOF; Kallay, AA; McIntyre, GJ; Wilson, CC
    A series of molecular complexes of the proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) with monosubstituted halobenzoic acids are reported, illustrating the designed exploitation of the characteristics of the proton sponge to induce short, charge-assisted hydrogen bonds in a predictable and reproducible manner. In every case, a DMAN molecule extracts a proton from the carboxylic acid group of the benzoic acid, as a result of which a recurrent supramolecular unit between a neutral and a deprotonated benzoic acid molecule is formed, featuring an extremely short, strong O–H···O hydrogen bond, within a predominant crystallization ratio of 1:2 (DMAN:benzoic acid). © 2016 American Chemical Society
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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.
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    Tuning proton disorder in 3,5-dinitrobenzoic acid dimers: the effect of local environment
    (American Chemical Society, 2013-01-04) Jones, AOF; Blagden, N; McIntyre, GJ; Parkin, A; Seaton, CC; Thomas, LH; Wilson, CC
    The carboxylic acid dimer is a frequently observed intermolecular association used in crystal engineering and design, which can show proton disorder across its hydrogen bonds. Proton disorder in benzoic acid dimers is a dynamic, temperature-dependent process whose reported occurrence is still relatively rare. A combination of variable temperature X-ray and neutron diffraction has been applied to demonstrate the effect of local crystalline environment on both the degree and onset of proton disorder in 3,5-dinitrobenzoic acid dimers. Dimers which have significantly asymmetric local intermolecular interactions are found to have a higher onset temperature for occupation of a second hydrogen atom site to be observed, indicating a greater energy asymmetry between the two configurations. Direct visualization of the electron density of hydrogen atoms within these dimers using high resolution X-ray diffraction data to characterize this disorder is shown to provide remarkably good agreement with that derived from neutron data. © 2013, American Chemical Society