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Charles J.
Mcmonagle
,
Priyanka
Comar
,
Gary S.
Nichol
,
David R.
Allan
,
Jesús
González
,
José A.
Barreda-argüeso
,
Fernando
Rodríguez
,
Rafael
Valiente
,
Gemma F.
Turner
,
Euan K.
Brechin
,
Stephen A.
Moggach
Open Access
Abstract: In situ single-crystal diffraction and spectroscopic techniques have been used to study a previously unreported Cu-framework bis[1-(4-pyridyl)butane-1,3-dione]copper(II) (CuPyr-I). CuPyr-I was found to exhibit high-pressure and low-temperature phase transitions, piezochromism, negative linear compressibility, and a pressure induced Jahn–Teller switch, where the switching pressure was hydrostatic media dependent.
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Aug 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[19178]
Open Access
Abstract: Despite possessing the desirable crystal packing and short Pt···Pt stacking distances required for a large piezoresistive response, the conductivity-pressure response of the Magnus green salt [Pt(NH3)4][PtCl4] is extremely sluggish. Through a combination of high-pressure X-ray diffraction and hybrid-DFT solid state calculations this study demonstrates that the poor conductivity-pressure response is due to a low volumetric compression anisotropy, a relatively large ambient pressure band gap and a lack of dispersion in the conduction band. Ligand modification (from NH3 to NH2CH3) does not enhance the piezoresistive response, causing even lower anisotropy of the volumetric compression and an unexpected phase transition at above 2 GPa. This study demonstrates that consideration of frontier band dispersion is a key design criterion, alongside crystal packing and Pt···Pt stacking distances for piezoresistive materials.
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Jul 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[19178]
Open Access
Abstract: Bis(1,2-dionedioximato) complexes of Pt(II) are known for their propensity to form linear chains of metal complexes in the solid state, and under the application of pressure members of the family display interesting optical and conductive properties. Two examples, Pt(bqd)2 and Pt(dmg)2, are known to undergo insulator-to-metal-to-insulator transitions, with the metallic state reached at 0.8–1.4 GPa and 5 GPa, respectively. Previous interpretations of these materials’ behaviour focused on the role of the filled dz2 and vacant p orbitals on platinum, with little consideration to the role of the ligand. Here, the pressure-structural behaviour of Pt(bqd)2 is investigated through single crystal X-ray diffraction, the first such study on this material. The difference in conductive behaviour under pressure between Pt(bqd)2 and Pt(dmg)2 is then interpreted through a combination of experimental and computational methods, including conductivity measurements under high pressure and electronic structure calculations. Our computational work reveals the significant contribution from ligand low-lying vacant π-orbitals to the frontier orbitals and bands in these complexes, and provides an explanation for the experimentally observed re-entrant insulator-to-metal-to-insulator transitions, and the differences in behaviour between the two compounds.
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Mar 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[9816, 8945]
Abstract: The synthesis of conventional porous crystals involves building a framework using reversible chemical bond formation, which can result in hydrolytic instability. In contrast, porous molecular crystals assemble using only weak intermolecular interactions, which generally do not provide the same environmental stability. Here, we report that the simple co-crystallization of a phthalocyanine derivative and a fullerene (C60 or C70) forms porous molecular crystals with environmental stability towards high temperature and hot aqueous base or acid. Moreover, by using diamond anvil cells and synchrotron single-crystal measurements, stability towards extreme pressure (>4 GPa) is demonstrated, with the stabilizing fullerene held between two phthalocyanines and the hold tightening at high pressure. Access to open metal centres within the porous molecular co-crystal is demonstrated by in situ crystallographic analysis of the chemisorption of pyridine, oxygen and carbon monoxide. This suggests strategies for the formation of highly stable and potentially functional porous materials using only weak van der Waals intermolecular interactions.
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May 2019
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I19-Small Molecule Single Crystal Diffraction
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Abstract: Many zeolitic imidazolate frameworks (ZIFs) are promising candidates for use in separation technologies. Comprising large cavities interconnected by small windows they can be used, at least in principle, as molecular sieves where molecules smaller than the window size are able to diffuse into the material while larger are rejected. However, “swing effect” or “gate opening” phenomena resulting in an enlargement of the windows have proven to be detrimental. Here, we present the first systematic experimental and computational study of the effect of chemical functionalisation of the imidazole linker on the framework dynamics. Using high-pressure (HP) single-crystal X-ray diffraction, density functional theory, and grand canonical Monte Carlo simulations, we show that in the isostructural ZIF-8, ZIF-90 and ZIF-65 functional groups of increasing polarity (-CH3,-CHO, -NO2) on the imidazole linkers provide control over the degree of rotation and thus the critical window diameter. On application of pressure, the substituted imidazolate rings rotate resulting in an increase in both pore volume and content. Our results show that the interplay between the guest molecules and the chemical function of the imidazole linker is essential for directing the swing effect in ZIF frameworks and therefore the adsorption performance.
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Dec 2017
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[9700]
Abstract: By decoupling the mechanical behaviour of building units for the first time in a wine-rack framework containing two different strut types, we show that lithium l-tartrate exhibits NLC with a maximum value, Kmax = -21 TPa-1, and an overall NLC capacity, ΧNLC = 5.1 %, that are comparable to the most exceptional materials to date. Furthermore, the contributions from molecular strut compression and angle opening interplay to give rise to so-called “hidden” negative linear compressibility, in which NLC is absent at ambient pressure, switched on at 2 GPa and sustained up to the limit of our experiment, 5.5 GPa. Analysis of the changes in crystal structure using variable-pressure synchrotron X-ray diffraction reveals new chemical and geometrical design rules to assist the discovery of other materials with exciting hidden anomalous mechanical properties.
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Jan 2017
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I19-Small Molecule Single Crystal Diffraction
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Christopher H.
Woodall
,
Gavin A.
Craig
,
Alessandro
Prescimone
,
Martin
Misek
,
Joan
Cano
,
Juan
Faus
,
Michael R.
Probert
,
Simon
Parsons
,
Stephen
Moggach
,
José
Martínez-lillo
,
Mark
Murrie
,
Konstantin V.
Kamenev
,
Euan K.
Brechin
Diamond Proposal Number(s):
[11879]
Open Access
Abstract: Materials that demonstrate long-range magnetic order are synonymous with information storage and the electronics industry, with the phenomenon commonly associated with metals, metal alloys or metal oxides and sulfides. A lesser known family of magnetically ordered complexes are the monometallic compounds of highly anisotropic d-block transition metals; the ‘transformation’ from isolated zero-dimensional molecule to ordered, spin-canted, three-dimensional lattice being the result of through-space interactions arising from the combination of large magnetic anisotropy and spin-delocalization from metal to ligand which induces important intermolecular contacts. Here we report the effect of pressure on two such mononuclear rhenium(IV) compounds that exhibit long-range magnetic order under ambient conditions via a spin canting mechanism, with Tc controlled by the strength of the intermolecular interactions. As these are determined by intermolecular distance, ‘squeezing’ the molecules closer together generates remarkable enhancements in ordering temperatures, with a linear dependence of Tc with pressure.
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Dec 2016
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I19-Small Molecule Single Crystal Diffraction
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Claire
Hobday
,
Ross James
Marshall
,
Colin F.
Murphie
,
Jorge
Sotelo
,
Tom
Richards
,
Dave
Allan
,
Tina
Düren
,
François- Xavier
Coudert
,
Ross
Forgan
,
Carole A.
Morrison
,
Stephen
Moggach
,
Thomas
Bennett
Abstract: Whilst many metal–organic frameworks possess the chemical stability needed to be used as functional materials, they often lack the physical strength required for industrial applications. Herein, we have investigated the mechanical properties of two UiO-topology Zr-MOFs, the planar UiO-67 ([Zr6O4(OH)4(bpdc)6], bpdc: 4,4′-biphenyl dicarboxylate) and UiO-abdc ([Zr6O4(OH)4(abdc)6], abdc: 4,4′-azobenzene dicarboxylate) by single-crystal nanoindentation, high-pressure X-ray diffraction, density functional theory calculations, and first-principles molecular dynamics. On increasing pressure, both UiO-67 and UiO-abdc were found to be incompressible when filled with methanol molecules within a diamond anvil cell. Stabilization in both cases is attributed to dynamical linker disorder. The diazo-linker of UiO-abdc possesses local site disorder, which, in conjunction with its longer nature, also decreases the capacity of the framework to compress and stabilizes it against direct compression, compared to UiO-67, characterized by a large elastic modulus. The use of non-linear linkers in the synthesis of UiO-MOFs therefore creates MOFs that have more rigid mechanical properties over a larger pressure range.
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Feb 2016
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I19-Small Molecule Single Crystal Diffraction
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Claire
Hobday
,
Ross James
Marshall
,
Colin F.
Murphie
,
Jorge
Sotelo
,
Tom
Richards
,
Dave
Allan
,
Tina
Düren
,
François-xavier
Coudert
,
Ross
Forgan
,
Carole A.
Morrison
,
Stephen
Moggach
,
Thomas
Bennett
Abstract: Whilst many metal–organic frameworks possess the chemical stability needed to be used as functional materials, they often lack the physical strength required for industrial applications. Herein, we have investigated the mechanical properties of two UiO-topology Zr-MOFs, the planar UiO-67 ([Zr6O4(OH)4(bpdc)6], bpdc: 4,4′-biphenyl dicarboxylate) and UiO-abdc ([Zr6O4(OH)4(abdc)6], abdc: 4,4′-azobenzene dicarboxylate) by single-crystal nanoindentation, high-pressure X-ray diffraction, density functional theory calculations, and first-principles molecular dynamics. On increasing pressure, both UiO-67 and UiO-abdc were found to be incompressible when filled with methanol molecules within a diamond anvil cell. Stabilization in both cases is attributed to dynamical linker disorder. The diazo-linker of UiO-abdc possesses local site disorder, which, in conjunction with its longer nature, also decreases the capacity of the framework to compress and stabilizes it against direct compression, compared to UiO-67, characterized by a large elastic modulus. The use of non-linear linkers in the synthesis of UiO-MOFs therefore creates MOFs that have more rigid mechanical properties over a larger pressure range.
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Jan 2016
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I19-Small Molecule Single Crystal Diffraction
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Open Access
Abstract: A cryogenic technique for loading a porous metal–organic framework with gas molecules is described by S. A. Moggach et al. in their Communication on page 13332 ff. The technique, usually used by physicists and planetary scientists, involves loading gases cryogenically into a diamond anvil cell. Here, both CO2 and CH4 were loaded into a scandium-based MOF. On increasing pressure the presence of a previously unobserved adsorption site was elucidated, and the pores were “superfilled” with guest molecules at room temperature.
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Nov 2015
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