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ABSTRACT: RUM with a twist: The magnitude of negative thermal expansion (NTE) in the LnCo(CN)6 coordination frameworks increases with Ln ion radius rLn . The framework structure contains an unusual locally unstable trigonal prismatic LnN6 unit that participates in an NTE-contributing vibrational mode by twisting about its axis at low energies. This contrasts with the rigid unit modes (RUMs) prevalent in other systems.
Angewandte Chemie International Edition 04/2013; · 13.45 Impact Factor
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ABSTRACT: A new microporous framework, Zn(NDC)(DPMBI) (where NDC = 2,7-naphthalene dicarboxylate and DPMBI = N,N'-di-(4-pyridylmethyl)-1,2,4,5-benzenetetracarboxydiimide), containing the redox-active benzenetetracarboxydiimide (also known as pyromellitic diimide) ligand core has been crystallographically characterised and exhibits a BET surface area of 608.2 ± 0.7 m(2) g(-1). The crystallinity of the material is retained upon chemical reduction with sodium naphthalenide (NaNp), which generates the monoradical anion of the pyromellitic diimide ligand in the framework Zn(NDC)(DPMBI)·Nax (where x represents the molar Na(+)/Zn(2+) ratio of 0.109, 0.233, 0.367 and 0.378 from ICP-AES), as determined by EPR, solid state Vis-NIR spectroelectrochemistry and UV-Vis-NIR spectroscopy. The CO2 uptake in the reduced materials relative to the neutral framework is enhanced up to a Na(+)/Zn(2+) molar ratio of 0.367; however, beyond this concentration the surface area and CO2 uptake decrease due to pore obstruction. The CO2 isosteric heat of adsorption (|Qst|) and CO2/N2 selectivity (S), obtained from pure gas adsorption isotherms and Ideal Adsorbed Solution Theory (IAST) calculations, are also maximised relative to the neutral framework at this concentration of the alkali metal counter-ion. The observed enhancement in the CO2 uptake, selectivity and isoteric heat of adsorption has been attributed to stronger interactions between CO2 and both the radical DPMBI ligand backbone and the occluded Na(+) ions.
Dalton Transactions 03/2013; · 3.84 Impact Factor
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ABSTRACT: Powder diffraction is used to study thermal expansion properties of MOF-5 at moderate helium gas pressures: 1.7 bar (100-500 K) and 5-150 bar (150-300 K). The framework shows negative thermal expansion (NTE) at all pressures, but vibrational motions causing NTE are damped with increasing pressures, leading to decreased NTE.
Chemical Communications 12/2012; · 6.17 Impact Factor
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Nina Lock,
Mogens Christensen,
Yue Wu,
Vanessa K Peterson,
Maja K Thomsen,
Ross O Piltz,
Anibal J Ramirez-Cuesta,
Garry J McIntyre,
Katarina Norén,
Ramzi Kutteh, Cameron J Kepert,
Gordon J Kearley,
Bo B Iversen
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ABSTRACT: Complementary experimental techniques and ab initio calculations were used to determine the origin and nature of negative thermal expansion (NTE) in the archetype metal-organic framework MOF-5 (Zn(4)O(1,4-benzenedicarboxylate)(3)). The organic linker was probed by inelastic neutron scattering under vacuum and at a gas pressure of 175 bar to distinguish between the pressure and temperature responses of the framework motions, and the local structure of the metal centers was studied by X-ray absorption spectroscopy. Multi-temperature powder- and single-crystal X-ray and neutron diffraction was used to characterize the polymeric nature of the sample and to quantify NTE over the large temperature range 4-400 K. Ab initio calculations complement the experimental data with detailed information on vibrational motions in the framework and their correlations. A uniform and comprehensive picture of NTE in MOF-5 has been drawn, and we provide direct evidence that the main contributor to NTE is translational transverse motion of the aromatic ring, which can be dampened by applying a gas pressure to the sample. The linker motion is highly correlated rather than local in nature. The relative energies of different framework vibrations populated in MOF-5 are suggested by analysis of neutron diffraction data. We note that the lowest-energy motion is a librational motion of the aromatic ring which does not contribute to NTE. The libration is followed by transverse motion of the linker and the carboxylate group. These motions result in unit-cell contraction with increasing temperature.
Dalton Transactions 10/2012; · 3.84 Impact Factor
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ABSTRACT: Multistability is exhibited by a metal-organic framework material that undergoes unique three-step spin crossover with 20 K thermal hysteresis. The stepwise transition is coupled to a three-step structural transformation that defines four distinct structural states. The material also exhibits reversible photo-induced spin crossover.
Angewandte Chemie International Edition 09/2012; 51(40):10154-8. · 13.45 Impact Factor
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ABSTRACT: The metal-organic framework Ni(2)(dobdc) (CPO-27-Ni, where dobdc = 1,4-dioxido-2,5-benzenedicarboxylate) has been post-synthetically modified with piperazine (pip) - a known 'accelerator' to improve the kinetics of CO(2) uptake in alkanolamine solvents for chemical absorption - and the impact of the modification on the CO(2) uptake and selectivity over N(2) has been probed. While the modified framework, Ni(2)(dobdc)(pip)(0.5) (pip-CPO-27-Ni), exhibits a lower uptake of CO(2) compared with the non-grafted material, the selectivity for CO(2) over N(2) at 25 °C and at pressures pertinent to post-combustion flue gas capture (0.1-0.15 bar) is enhanced. Mechanistically, the interaction between the CO(2) molecules and the free amine sites in pip-CPO-27-Ni occurs via physisorption and chemisorption interactions, in which CO(2) binds to the framework with an isosteric heat of adsorption (-Q(st)) of 40.5 kJ mol(-1) at very low coverage (P = 0.033 mbar), followed by binding at a higher heat of adsorption (-Q(st) = 46.2 kJ mol(-1) at P = 3.55 mbar). Pure water adsorption isotherms revealed a two-step mechanism for uptake in CPO-27-Ni, consistent with adsorption into the first and second hydration spheres of Ni(2+) followed by subsequent uptake via physisorption into the pores. Additional steric hindrance in pip-CPO-27-Ni results in a single step only. The working capacity over multiple cycles was also investigated using a temperature swing adsorption process which revealed reversible CO(2) adsorption and desorption of 10 wt% over 10 cycles.
Dalton Transactions 08/2012; 41(38):11739-44. · 3.84 Impact Factor
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ABSTRACT: A new discrete [V(16)O(38)(CN)](9-) cluster, which displays the hitherto unknown 8- charge on the cluster shell and is the first to encapsulate the cyanide anion, has been synthesized and characterized by IR and UV/vis/near-IR spectroscopy, electrochemistry, and magnetic susceptibility measurements. Bond valence sum calculations conducted on the basis of the crystal structure analysis of K(9)[V(16)O(38)(CN)]·13H(2)O confirm that this new member of the polyoxovanadate series is a mixed-valence complex. The intervalence charge transfer bands arising from intrametal interactions reveal that a localized (class II) assignment is appropriate for the cluster; however, a small degree of electronic delocalization is present. Interesting possibilities exist for the incorporation of this unit into higher dimensionality framework structures, where the redox, optical, and magnetic properties can be exploited and tuned.
Inorganic Chemistry 04/2012; 51(17):9192-9. · 4.60 Impact Factor
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ABSTRACT: Three high-spin tetranuclear cobalt(II) complexes have been prepared with the bridging ligand 4,7-phenanthrolino-5,6:5',6'-pyrazine (ppz) through metal-ion directed self-assembly. The complexes differ by the incorporation of three different coordinating anions: chloride, thiocyanide and selenocyanide. The physical properties of these complexes have been investigated in detail.
Dalton Transactions 12/2011; 40(45):12388-93. · 3.84 Impact Factor
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ABSTRACT: Cyanidometallate complexes are highly versatile building units for the generation of functional porous materials. Here we report five new pillared Hofmann layer compounds incorporating the tetracyanidometallates [MoO(CN)(4)](2-) and [MnN(CN)(4)](2-). These metalloligands, which are new to this class of materials, have been combined with divalent 1st-row transition metals to produce Hofmann layers that are linked into three-dimensional frameworks by ditopic bridging dipyridyls. We report the structures and anomalous thermal expansion properties of five new materials: [Mn(H(2)O)(bpy)(½){MoO(CN)(4)(bpy)(½)}]·2H(2)O (1), [Mn(H(2)O)(bpy)(½){MnN(CN)(4)(bpy)(½)}]·2H(2)O (2), [Fe(H(2)O)(bpy)(½){MnN(CN)(4)(bpy)(½)}]·2H(2)O (3), [Co(H(2)O)(bpy)(½){MnN(CN)(4)(bpy)(½)}]·2H(2)O (4) and [{Mn(H(2)O)(2)}(½){Mn(bpa)(2)}(½){MoO(CN)(4)(bpa)(½)}]·MeOH (5), (where bpy = 4,4'-bipyridine and bpa = 4,4'-bipyridylacetylene).
Dalton Transactions 09/2011; 40(43):11621-8. · 3.84 Impact Factor
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ABSTRACT: In this article, techniques for separating mixtures of insoluble compounds are discussed with respect to the small quantities found in laboratory preparations, as opposed to industrial quantities. The techniques include separations based on density, surface area and differences in particle size. Also discussed are simple apparatus, readily available in the laboratory or from commercial suppliers, for achieving these techniques.
Dalton Transactions 05/2011; 40(27):7122-6. · 3.84 Impact Factor
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ABSTRACT: D2 loaded to saturation at 25 K into the porous coordination framework Cu3(1,3,5-benzenetricarboxylate)2 was studied using neutron powder diffraction. A saturation loading equivalent to 6.1 wt % H2 is reached at 25 K. D2 is located at up to nine distinct sites with six stable at saturation and three “metastable” sites at doses intermediate to saturation. Filling of the trimodal pore system is complex, and a concentration dependency on the optimal D2 arrangement is noted. A dynamic rearrangement of the D2 in the pores to a cubic-closed packed equilibrium structure occurs at doses close to saturation, with 4 D2 molecules arranged tetrahedrally in the smallest pore, 32 D2 arranged in a truncated octahedron with capped hexagonal faces in the intermediate sized pore, and 48 D2 arranged in a face-capped rhombic dodecahedron in the largest pore. The equilibrium structure of D2 in the largest pore at doses close to and at saturation was found to be the same arrangement that is optimal for 48 circles on a sphere. The structural response of the framework to D2 adsorption is dependent on the amount of D2, where the host lattice expands with increasing amount of adsorbed D2 at low and high D2 doses, and contracts upon adsorption of intermediate amounts of D2, commensurate with the known flexibility exhibited by this framework.
04/2011;
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Angewandte Chemie International Edition 03/2011; 50(12):2820-3. · 13.45 Impact Factor
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ABSTRACT: An unusual discrete heteronuclear metallomacrocycle was designed and synthesized via metal-ion-directed self-assembly by an iron(II) template. The formation of this metallomacrocycle was demonstrated by X-ray crystallography, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, and NMR spectroscopy.
Inorganic Chemistry 02/2011; 50(3):726-8. · 4.60 Impact Factor
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ABSTRACT: Multi-temperature X-ray diffraction studies show that twisting, rotation, and libration cause negative thermal expansion (NTE) of the nanoporous metal−organic framework MOF-5, Zn4O(1,4-benzenedicarboxylate)3. The near-linear lattice contraction is quantified in the temperature range 80−500 K using synchrotron powder X-ray diffraction. Vibrational motions causing the abnormal expansion behavior are evidenced by shortening of certain interatomic distances with increasing temperature according to single-crystal X-ray diffraction on a guest-free crystal over a broad temperature range. Detailed analysis of the atomic positional and displacement parameters suggests two contributions to cause the effect: (1) local twisting and vibrational motion of the carboxylate groups and (2) concerted transverse vibration of the linear linkers. The vibrational mechanism is confirmed by calculations of the dynamics in a molecular fragment of the framework.
09/2010;
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Hui Wu,
Jason M Simmons,
Yun Liu,
Craig M Brown,
Xi-Sen Wang,
Shengqian Ma,
Vanessa K Peterson,
Peter D Southon, Cameron J Kepert,
Hong-Cai Zhou,
Taner Yildirim,
Wei Zhou
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ABSTRACT: Metal-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 CH(4) 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 unambiguously 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.
Chemistry 03/2010; 16(17):5205-14. · 5.93 Impact Factor
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ABSTRACT: We previously reported the dinuclear material [Fe(II) (2)(ddpp)(2)(NCS)(4)] x 4 CH(2)Cl(2) (1 x 4 CH(2)Cl(2); ddpp = 2,5-di(2',2''-dipyridylamino)pyridine) and its partially desolvated analogue (1 x CH(2)Cl(2)), which undergo two- and one-step spin-crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one- or two-step spin transition can be specifically targeted. The chloroform clathrate 1 x 4 CHCl(3) undergoes a relatively abrupt one-step SCO, in which the two equivalent Fe(II) sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1 x 4 CHCl(3) to form 1 x 3 CHCl(3) and 1 x CHCl(3) occurs through single-crystal-to-single-crystal processes (monoclinic C2/c to P2(1)/n to P2(1)/n) in which the two equivalent Fe(II) sites become inequivalent sites within the dinuclear molecule of each phase. Both 1 x 3 CHCl(3) and 1 x CHCl(3) undergo one-step spin transitions, with the former having a significantly higher SCO temperature than 1 x 4 CHCl(3) and the latter, and each has a broader SCO transition than 1 x 4 CHCl(3), attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials through reversibly resolvating the partially desolvated material with chloroform to produce the original one-step SCO, or with dichloromethane to produce a two-step SCO reminiscent of that seen for 1 x 4 CH(2)Cl(2). Furthermore, we investigate the light-induced excited spin state trapping (LIESST) effect on 1 x 4 CH(2)Cl(2) and 1 x CH(2)Cl(2) and observe partial LIESST activity for the former and no activity for the latter.
Chemistry 02/2010; 16(6):1973-82. · 5.93 Impact Factor
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Jack K Clegg,
Simon S Iremonger,
Michael J Hayter,
Peter D Southon,
René B Macquart,
Martin B Duriska,
Paul Jensen,
Peter Turner,
Katrina A Jolliffe, Cameron J Kepert,
George V Meehan,
Leonard F Lindoy
Angewandte Chemie International Edition 02/2010; 49(6):1075-8. · 13.45 Impact Factor
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Angewandte Chemie International Edition 12/2009; 49(3):585-8. · 13.45 Impact Factor
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ABSTRACT: Tetramethylammonium copper(I) zinc(II) cyanide, which consists of N(CH(3))(4)(+) ions trapped within a cristobalite-like metal cyanide framework, has been studied by variable-temperature powder and single-crystal X-ray diffraction. Its coefficient of thermal expansion is approximately zero over the temperature range 200-400 K and comparable with the best commercial zero thermal expansion materials. The atomic displacement parameters, apparent bond lengths, and structure of a low-temperature, low-symmetry phase reveal that the low-energy vibrational modes responsible for this behavior maintain approximately rigid Zn coordination tetrahedra but involve significant distortion of their Cu counterparts.
Journal of the American Chemical Society 12/2009; 132(1):10-1. · 9.91 Impact Factor
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ABSTRACT: The electronic switching properties of the nanoporous spin crossover framework [Fe(NCS)(2)(bpbd)(2)] x x(guest), SCOF-2, can be rationally manipulated via sorption of a range of molecular guests (acetone, ethanol, methanol, propanol, 1-acetonitrile) into the 1-D channels of this material. Pronounced changes to the spin crossover properties are related directly to the steric and electronic influence of the individual guests: the degree of lattice cooperativity, as reflected in the abruptness of the transition and presence of hysteresis, is strongly influenced by the presence of cooperative host-guest interactions, and the temperature of the transition varies with guest polarity through a proposed electrostatic interaction.
Journal of the American Chemical Society 10/2009; 131(34):12106-8. · 9.91 Impact Factor
