Browsing by Author "Ramirez-Cuesta, AJ"
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- ItemHydrogen adsorption strength and sites in the metal organic framework MOF5: comparing experiment and model calculations(Elsevier, 2008-07-03) Mulder, FM; Dingemans, TJ; Schimmel, HG; Ramirez-Cuesta, AJ; Kearley, GJHydrogen adsorption in porous, high surface area, and stable metal organic frameworks (MCF's) appears a novel route towards hydrogen storage materials [N.L. Rosij Eckert, M. Eddaoudi, D.T. Voclakj Kim M., O'Keeffe, O.M. Yaghi, Science 300 (2003) 1127: J.L.C. Rowsell, A.R. Millward, K. Sung Park O.M. Yaghi J,,. Am. Chem. Soc. 126 (2004) 5666; G. Ferey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guegan, Chem. Commun. (2003) 2976; T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry T., Bataille, G. Ferey, Chem. Eur. J. 10 (2004) 1373]. A prerequisite for such materials is sufficient adsorption interaction strength for hydrogen adsorbed on the adsorption sites of the material because this facilitates successful operation under moderate temperature and pressure conditions. Here we report detailed information on the geometry of the hydrogen adsorption sites, based on the analysis of inelastic neutron spectroscopy (INS). The adsorption energies for the metal organic framework MOF5 equal about 800 K for part of the different sites, which is significantly higher than for narroporous carbon materials (-550 K) [H.G. Schimmel, GJ. Kearley, M.G. Nijkamp, C.T. Visser, K.P. de Jong, F.M. Mulder, Chem. Eur. J. 9 (2003) 4764], and is in agreement with what is found in first principles calculations [T. Sagara, J. Klassen, E. Ganz, J. Chem. Phys. 121 (2004) 12543; F.M. Mulder, T.J. Dingernans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113]. Assignments orthe INS spectra is realized using comparison with independently published model calculations [F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113] and structural data IT. Yildirim, M.R. Hartman, Phys. Rev. Lett. 95 (2005) 215504]. © 2008, Elsevier Ltd.
- ItemLocal vibrational mechanism for negative thermal expansion: a combined neutron scattering and first-principles study(Wiley-VCH Verlag Berlin, 2010-01-12) Peterson, VK; Kearley, GJ; Wu, Y; Ramirez-Cuesta, AJ; Kemner, E; Kepert, CJAsk the locals: dynamic deformation of the dicopper tetracarboxylate paddlewheel unit within a metal-organic framework from square-prismatic to distorted occurs at very low energies. This deformation, which contributes strongly to the negative thermal expansion of this system, is a local vibration induced by a redistribution of electron density at the CuO junctions. © 2010, Wiley-VCH Verlag Berlin
- ItemNegative thermal expansion in LnCo(CN)6 (Ln=La, Pr, Sm, Ho, Lu, Y): mechanisms and compositional trends(John Wiley and Sons, 2013-04-09) Duyker, SG; Peterson, VK; Kearley, GJ; Ramirez-Cuesta, AJ; Kepert, CJNegative thermal expansion (NTE) is a comparatively rare phenomenon that is found in a growing number of materials.1 The discovery of new NTE materials and the elucidation of mechanisms underpinning their behavior is important both in extending the field and enabling tailored thermal expansion properties. NTE has been found throughout a broad family of cyanide coordination frameworks,2 arising from thermal population of low-energy transverse vibrations of the cyanide bridges, which reduce the average metal–metal distances, and thus the lattice parameters, with increasing temperature. More complex mechanisms have been established in metal–organic framework materials, in which both local and long-range modes contribute to NTE.3 The low-energy dynamics of metal-based materials are often modeled in terms of rigid unit modes (RUMs), wherein the metal-centered polyhedra are treated as rigid, with only the linkage being flexible. © 2013, Wiley-Vch Verlag GmbH & Co.
- ItemScrutinizing negative thermal expansion in MOF-5 by scattering techniques and ab initio calculations(Royal Society of Chemistry, 2012-09-14) Lock, N; Christensen, M; Wu, Y; Peterson, VK; Thomsen, MK; Piltz, RO; Ramirez-Cuesta, AJ; McIntyre, GJ; Noren, K; Kutteh, R; Kepert, CJ; Kearley, GJ; Iversen, BBComplementary 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 (Zn4O(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. © 2012, Royal Society of Chemistry