Browsing by Author "Southon, PD"
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- ItemGuest adsorption in the nanoporous metal–organic framework Cu3(1,3,5-benzenetricarboxylate)2: combined in situ x-ray diffraction and vapor sorption(American Chemical Society, 2014-07-23) Peterson, VK; Southon, PD; Halder, GJ; Price, DJ; Bevitt, JJ; Kepert, CJThe structure of the nanoporous metal–organic framework Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) with a variety of molecular guests was studied in situ using single crystal X-ray diffraction. By collecting crystal structure data for a series of guests within the same host crystal, insights into the molecular interactions underpinning guest adsorption processes have been gained. Adsorption behaviors are influenced strongly by both enthalpic and entropic thermodynamic, as well as interpore steric (size-exclusion) effects, and we note correlations between guest attributes and these effects. Vapor adsorption measurements revealed a guest uptake capacity inversely proportional to guest size. Correspondingly, structural results show that guests reside in the smallest pores accessible to them. Interpore steric effects for larger guests cause these to be excluded from the smallest pores, and this corresponds to lower total uptake. Both hydrophilic and lipophilic small guests adsorb favorably into the 5 Å diameter smallest pore of the material, with the number of guests in these pores dependent on guest size and their location, in turn dependent upon both guest–guest interactions and competition between hydrogen-bonding interactions at the apertures of the smallest pore and lipophilic interactions at the center of the smallest pore. Hydrophilic guests with lone electron pairs interact preferentially with the coordinatively unsaturated Cu sites of the desolvated framework, with the number of these depending on steric interactions between neighboring bound guests and guest flexibility. Guest coordination at the Cu sites has a significant effect on the framework structure, increasing the Cu···Cu distance in the dinuclear unit, with the Cu3(BTC)2 unit cell being smaller when guests that do not coordinate with the Cu are present, and in the case of cyclohexane, smaller than for the desolvated framework. Overall, our comprehensive structural study reconciles Cu3(BTC)2 adsorption properties with the underlying guest–host and guest–guest interactions that gives rise to these. © 2014, American Chemical Society.
- ItemHost–guest adsorption behavior of deuterated methane and molecular oxygen in a porous rare-earth metal–organic framework(Cambridge Core, 2014-11-17) Ogilvie, SH; Duyker, SG; Southon, PD; Peterson, VK; Kepert, CJThe yttrium-based metal–organic framework, Y(btc) (btc = 1,3,5-benzenetricarboxylate), shows moderate uptake of methane (0.623 mmol g−1) and molecular oxygen (0.183 mmol g−1) at 1 bar and 308 K. Neutron powder-diffraction data for the guest-free, CD4-, and O2-loaded framework reveal multiple adsorption sites for each gas. Both molecular guests exhibit interactions with the host framework characterised by distances between the framework and guest atoms that range from 2.83 to 4.81 Å, with these distances identifying interaction most commonly between the guest molecule and the carboxylate functional groups of the benzenetricarboxylate bridging ligand of the host. © 2014, International Centre for Diffraction Data.
- ItemIdentification of bridged CO2 binding in a Prussian blue analogue using neutron powder diffraction(Royal Society of Chemistry, 2013-01-01) Ogilvie, SH; Duyker, SG; Southon, PD; Peterson, VK; Kepert, CJNeutron powder diffraction measurements were carried out on the evacuated and CO2-loaded Prussian blue analogue, Fe3[Co(CN)6]2, identifying two distinct CO2 adsorption sites: site A, in which CO2 uniquely bridges between two bare-metal sites, and site B, in which it interacts in a face capping motif. The saturation of site A at low loadings of CO2 demonstrates the favourable nature of the interaction of CO2 with bare-metal sites within the material. © 2013, Royal Society of Chemistry.
- ItemMetal-organic frameworks with exceptionally high methane uptake: where and how is methane stored?(Wiley-VCH Verlag Berlin, 2010-05-03) Wu, H; Simmons, JM; Liu, Y; Brown, CM; Wang, XS; Ma, S; Peterson, VK; Southon, PD; Kepert, CJ; Zhou, HC; Yildirim, T; Zhou, WMetal–organic frameworks (MOFs) are a novel family of physisorptive materials that have exhibited great promise for methane storage. So far, a detailed understanding of their methane adsorption mechanism is still scarce. Herein, we report a comprehensive mechanistic study of methane storage in three milestone MOF compounds (HKUST-1, PCN-11, and PCN-14) the CH4 storage capacities of which are among the highest reported so far among all porous materials. The three MOFs consist of the same dicopper paddlewheel secondary building units, but contain different organic linkers, leading to cagelike pores with various sizes and geometries. From neutron powder diffraction experiments and accurate data analysis, assisted by grand canonical Monte Carlo (GCMC) simulations and DFT calculations, we anambiguously revealed the exact locations of the stored methane molecules in these MOF materials. We found that methane uptake takes place primarily at two types of strong adsorption site: 1) the open Cu coordination sites, which exhibit enhanced Coulomb attraction toward methane, and 2) the van der Waals potential pocket sites, in which the total dispersive interactions are enhanced due to the molecule being in contact with multiple “surfaces”. Interestingly, the enhanced van der Waals sites are present exclusively in small cages and at the windows to these cages, whereas large cages with relatively flat pore surfaces bind very little methane. Our results suggest that further, rational development of new MOF compounds for methane storage applications should focus on enriching open metal sites, increasing the volume percentage of accessible small cages and channels, and minimizing the fraction of large pores. © 2010, Wiley-VCH Verlag Berlin
- ItemNegative thermal expansion in the metal-organic framework material Cu-3(1,3,5-benzenetricarboxylate)(2)(Wiley-VCH Verlag Berlin, 2008-08-08) Wu, Y; Kobayashi, A; Halder, GJ; Peterson, VK; Chapman, KW; Lock, N; Southon, PD; Kepert, CJThe metal–organic framework [Cu3(btc)2] displays negative thermal expansion (NTE) over a broad temperature range. This property arises from two coincident mechanisms, each of which are unique for NTE systems: the concerted transverse vibration of triangular organic linkers, and the local dynamic distortion of dinuclear metal centers within the framework lattice. © 2008, Wiley-VCH Verlag Berlin
- ItemPhase diagram, chemical stability and physical properties of the solid-solution Ba(4)Nb(2-x)Ta(x)O(9)(Academic Press INC Elsevier, 2011-10-01) Dunstan, MT; Southon, PD; Kepert, CJ; Hester, JR; Kimpton, JA; Ling, CDThrough the construction of the Ba4Nb2−xTaxO9 phase diagram, it was discovered that the unique high-temperature γ phase is a thermodynamic intermediate between the low-temperature α phase (Sr4Ru2O9-type) and a 6H-perovskite. Refined site occupancies for the γ phase across the Ba4Nb2−xTaxO9 solid-solution indicate that Nb preferentially occupies the tetrahedral sites over the octahedral sites in the structure. When annealed in a CO2-rich atmosphere, all of the phases studied absorb large amounts of CO2 at high temperatures between ∼ 700 and 1300 K. In situ controlled-atmosphere diffraction studies show that this behaviour is linked to the formation of BaCO3 on the surface of the material, accompanied by a Ba5(Nb,Ta)4O15 impurity phase. In situ diffraction in humid atmospheres also confirms that these materials hydrate below ∼ 1273 K , and that this plays a critical role in the various reconstructive phase transitions as well as giving rise to proton conduction.(C) 2011 Elsevier Inc.
- ItemTopotactic structural conversion and hydration-dependent thermal expansion in robust LnMIII(CN)6·nH2O and flexible ALnFeII(CN)6·nH2O frameworks (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; 0 ≤ n ≤ 5)(Royal Society of Chemistry, 2014-06-04) Duyker, SG; Halder, GJ; Southon, PD; Price, DJ; Edwards, AJ; Peterson, VK; Kepert, CJThe structures of the AxLnM(CN)6·nH2O (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; x = 0, 1; 0 ≤ n ≤ 5) cyanide frameworks, their thermal expansion behaviour, and their transformations upon dehydration are explored using X-ray and neutron single crystal diffraction and X-ray powder diffraction. Modification from positive to negative thermal expansion in the LnCo(CN)6·nH2O phases is achieved by removal of the guest water molecules. Most notable is the unprecedented flexibility demonstrated by the “coiling” of KLnFe(CN)6·nH2O frameworks upon their dehydration, wherein the lanthanoid coordination geometry reversibly converts from a 9-coordinate tri-capped trigonal prism to a 6-coordinate octahedron via a single-crystal-to-single-crystal process, accompanied by a large (14–16%) decrease in unit cell volume. © 2014, The Royal Society of Chemistry.
- ItemTuning pore size in a zirconium–tricarboxylate metal–organic framework(Royal Society of Chemistry, 2014-06-04) Liang, WB; Chevreau, H; Ragon, F; Southon, PD; Peterson, VK; D'Alessandro, DMThe water-stable zirconium–tricarboxylate series of frameworks, [Zr6O4(OH)4(X)6(btc)2]·nH2O, where X = formate (F), acetate (A), or propionate (P), exhibit tunable porosity by virtue of systematic modulation of the chain length of the monocarboxylate ligand X. This modification not only impacts the pore size of the framework, but provides an important avenue for the construction of mixed-linker MOFs. © 2014, The Royal Society of Chemistry.