Browsing by Author "Robson, R"

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    Copper(II) coordination polymers of imdc− (H2imdc+ = the 1,3-bis(carboxymethyl)imidazolium cation): unusual sheet interpenetration and an unexpected single crystal-to-single crystal transformation
    (Royal Society of Chemistry, 2013-10-08) Abrahams, BF; Maynard-Casely, HE; Robson, R; White, KF
    The monoanion of 1,3-bis(carboxymethyl)imidazolium (H2imdc+) combines with Cu(II) to produce an undulating 2D coordination polymer of composition [Cu2(imdc)2(CH3OH)2](BF4)2·(CH3OH)(H2O) (1) in which copper acetate-like dimers, linked by imdc− ligands, act as 4-connecting centres. Cationic sheets stack on top of each other in an A, B, A, B… fashion and produce a structure that contains channels running parallel to the plane of network. Tetrafluoroborate anions are located in channels between sheets. Upon removal of coordinated and noncoordinated solvent molecules a single crystal-to-single crystal transformation occurs to yield a similar compound but with BF4 − anions now coordinated. CO2 isotherms measured at 258 and 273 K show only modest uptake of CO2 but provide an indication that the sheets move apart at elevated pressures in order to accommodate the guest molecules. A compound of composition [Cu3(OH)2(imdc)2]·SiF6·2H2O·2MeOH (3), which possesses a 3D network, is formed by the combination of copper(II) acetate, copper(II) hexafluorosilicate and Himdc. In this structure infinite parallel Cu3(OH)2 chains are linked by bridging imdc− ligands to form channels that have an approximately triangular cross-section. These channels are occupied by SiF6 2− anions in addition to solvent molecules. When copper(II) acetate is combined with Himdc in the appropriate ratio, a 1D coordination polymer of composition Cu(imdc)2 (4) is formed in which pairs of imdc− anions bridge Cu(II) centres. When the reaction is performed in the presence of NaBF4 a minor crystalline product with tetragonal symmetry is isolated in addition to the 1D coordination polymer. This compound of composition Cu2(imdc)4NaBF4·7H2O (5) consists of 2D Cu(imdc)2 networks and features an unusual mode of interpenetration. © 2013, The Royal Society of Chemistry.
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    The effect of sterically active ligand substituents on gas adsorption within a family of 3D Zn-based coordination polymers
    (American Chemical Society, 2020-06-09) Abrahams, BF; Babarao, R; Dharma, AD; Holmes, JL; Hudson, TA; Maynard-Casely, HE; McGain, F; Robson, R; Waite, KF
    An investigation of the adsorption properties of two structurally related, 3D coordination polymers of composition Zn(2-Mehba) and Zn(2,6-Me2hba) (2-Mehba = the dianion of 2-methyl-4-hydroxybenzoic acid and 2,6-Me2hba = the dianion of 2,6-dimethyl-4-hydroxybenzoic acid) is presented. A common feature of these structures are parallel channels that are able to accommodate appropriately sized guest molecules. The structures differ with respect to the steric congestion within the channels arising from methyl groups appended to the bridging ligands of the network. The host network, Zn(2-Mehba), is able to take up appreciable quantities of H2 (77 K) and CO2 and CH4 (298 K) in a reversible manner. In regard to the adsorption of N2 by Zn(2-Mehba), there appears to be an unusual temperature dependence for the uptake of the gas such that when the temperature is increased from 77 to 298 K the uptake of N2 increases. The relatively narrow channels of Zn(2,6-Me2hba) are too small to allow the uptake of N2 and CH4, but H2 molecules can be adsorbed. A pronounced step at elevated pressures in CO2 and N2O isotherms for Zn(2,6-Me2hba) is noted. Calculations indicate that rotation of phenolate rings leads to a change in the available intraframework space during CO2 dosing. © 2020 American Chemical Society
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    Lattice response of the porous coordination framework Zn(hba) to guest adsorption
    (Cambridge University Press, 2017-09-05) Auckett, JE; Dharma, AD; Cagnes, MP; Darwish, TA; Abrahams, BF; Barbarao, R; Hudson, TA; Robson, R; White, KF; Peterson, VK
    Analysis of in situ neutron powder diffraction data collected for the porous framework material Zn(hba) during gas adsorption reveals a two-stage response of the host lattice to increasing CO2 guest concentration, suggesting progressive occupation of multiple CO2 adsorption sites with different binding strengths. The response of the lattice to moderate CH4 guest concentrations is virtually indistinguishable from the response to CO2, demonstrating that the influence of host–guest interactions on the Zn(hba) framework is defined more strongly by the concentration than by the identity of the guests. © International Centre for Diffraction Data 2017
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    Li+ and Ca2+ derivatives of the isonicotinate-n-oxide ion including single crystal-to-single crystal transformations
    (Americal Chemical Society, 2014-07-29) White, KF; Abrahams, BF; Maynard-Casely, HE; Robson, R
    Crystals of [Li(inox)(H2O)] (where inox– = the isonicotinate-N-oxide ion) are obtained from aqueous solution. The Li+ cations and the carboxylate anions form a two-dimensional (2D) sheet containing four-membered (−Li–O–Li–O−) rings and 16-membered (−Li–O–C–O−)4 rings; the sheets are linked to adjacent parallel sheets through hydrogen bonds. Crystals of solvent-free [Li(inox)], obtained from t-butanol, consist of a three-dimensional network which can also be prepared in microcrystalline form by dehydration of [Li(inox)(H2O)] at 200 °C. Crystals of [Ca(inox)2(H2O)2] contain 2D sheets with 4,4 topology in which Ca2+ ions, bound by trans water molecules, provide the 4-connecting nodes. The Ca(H2O)22+ units are linked by carboxylate groups to generate 16-membered (−Ca–O–C–O−)4 rings. Sheets are bound together by hydrogen bonds between the pyridine-N-oxide units and coordinated water molecules. [Ca(inox)2(H2O)2] can be dehydrated at 190 °C in a single crystal-to-single crystal transformation to give [Ca(inox)2] whose structure is related to that of the hydrated precursor. A proposed solid-state mechanism for this single crystal-to-single crystal transformation, in which the N-oxide takes up the site on calcium vacated by water is proposed © 2014 American Chemical Society.
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    Square grid metal–chloranilate networks as robust host systems for guest sorption
    (John Wiley & Sons, Inc, 2019-02-02) Kingsbury, CJ; Abrahams, BF; Auckett, JE; Chevreau, H; Dharma, AD; Duyker, SG; He, QL; Hua, C; Hudson, TA; Murray, KS; Phonsri, W; Peterson, VK; Robson, R; White, KF
    Reaction of the chloranilate dianion with Y(NO3)3 in the presence of Et4N+ in the appropriate proportions results in the formation of (Et4N)[Y(can)2], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can)2] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption. This compound exhibits a high affinity for volatile guest molecules, which could be identified within the framework by crystallographic methods. In situ neutron powder diffraction indicates a size-shape complementarity leading to a strong interaction between host and guest for CO2 and CH4. Single-crystal X-ray diffraction experiments indicate significant interactions between the host framework and discrete I2 or Br2 molecules. A series of isostructural compounds (cat)[MIII(X-an)2] with M=Sc, Gd, Tb, Dy, Ho, Er, Yb, Lu, Bi or In, cat=Et4N, Me4N and X-an=chloranilate, bromanilate or cyanochloranilate bridging ligands have been generated. The magnetic properties of representative examples (Et4N)[Gd(can)2] and (Et4N)[Dy(can)2] are reported with normal DC susceptibility but unusual AC susceptibility data noted for (Et4N)[Gd(can)2]. © 2019 Wiley-VCH Verlag GmbH & Co