I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[18735]
Abstract: The compound Cp(IPr)Ru(H)2SiH(Ph)Cl (IPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene) (1) was subject to low temperature (30 K), high resolution X-ray structural analysis to obtain a high quality electron density map. This map was subject to a Bader analysis to ascertain the possibility of a Ru–H⋯Si interaction. For comparison, DFT calculations employing the well known B3LYP functional in conjunction with a triple zeta basis set was employed. Thus, we not only report the results of a possible Ru–H⋯Si interaction but also benchmark the use of the employed level of theory against experimental results.
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Mar 2019
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I19-Small Molecule Single Crystal Diffraction
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C.
Delacotte
,
G. F. S.
Whitehead
,
M. J.
Pitcher
,
C. M
Robertson
,
P. M.
Sharp
,
M. S.
Dyer
,
Jo.
Alaria
,
J. B.
Claridge
,
G. R.
Darling
,
D. R.
Allan
,
G.
Winter
,
M. J.
Rosseinsky
Diamond Proposal Number(s):
[15777]
Open Access
Abstract: Hexaferrites are an important class of magnetic oxides with applications in data storage and electronics. Their crystal structures are highly modular, consisting of Fe- or Ba-rich close-packed blocks that can be stacked in different sequences to form a multitude of unique structures, producing large anisotropic unit cells with lattice parameters typically >100 Å along the stacking axis. This has limited atomic-resolution structure solutions to relatively simple examples such as Ba2Zn2Fe12O22, whilst longer stacking sequences have been modelled only in terms of block sequences, with no refinement of individual atomic coordinates or occupancies. This paper describes the growth of a series of complex hexaferrite crystals, their atomic-level structure solution by high-resolution synchrotron X-ray diffraction, electron diffraction and imaging methods, and their physical characterization by magnetometry. The structures include a new hexaferrite stacking sequence, with the longest lattice parameter of any hexaferrite with a fully determined structure.
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Nov 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11361]
Abstract: High pressure single-crystal X-ray structural analyses of isostructural MFM-133(M) (M = Zr, Hf) of flu topology and incorporating the tetracarboxylate ligand TCHB4– [H4TCHB = 3,3',5,5'-tetrakis(4-carboxyphenyl)-2,2',4,4',6,6'-hexamethyl-1,1'-biphenyl] and {M6(µ-OH)8(OH)8(COO)8} clusters, confirm negative linear compressibility (NLC) behavior along the c axis. This occurs via a three-dimensional wine-rack NLC mechanism leading to distortion of the octahedral cage towards a more elongated polyhedron under static compression. Despite the isomorphous nature of these two structures, MFM-133(Hf) shows a higher degree of NLC than the Zr(IV) analogue. Thus, for the first time, we demonstrate here an effective strategy for tuning NLC materials simply by varying the inorganic component of the frameworks.
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Feb 2018
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Abstract: The high-pressure structural behaviour of phosphoric acid is described. A compression study of the monoclinic phase, using neutron powder diffraction and X-ray single-crystal diffraction, shows that it converts to a previously unobserved orthorhombic phase on decompression. Compression of this new phase is reported up to 6.3 GPa. The orthorhombic phase is found to be more efficiently packed, with reduced void space, resulting in a larger bulk modulus. Molecule–molecule interaction energies reveal a more extensive network of increased attractive forces in the orthorhombic form relative to the monoclinic form, suggesting greater thermodynamic stability.
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Dec 2017
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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
Mechanical Engineering
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David R.
Allan
,
Harriott
Nowell
,
Sarah A.
Barnett
,
Mark R.
Warren
,
Adrian
Wilcox
,
Jeppe
Christensen
,
Lucy
Saunders
,
Andrew
Peach
,
Mark T.
Hooper
,
Ljubo
Zaja
,
Suren
Patel
,
Leo
Cahill
,
Russell
Marshall
,
Steven
Trimnell
,
Andrew
Foster
,
Trevor
Bates
,
Simon
Lay
,
Mark A.
Williams
,
Paul V.
Hathaway
,
Graeme
Winter
,
Markus
Gerstel
,
Ron
Wooley
Open Access
Abstract: Herein, we describe the development of a novel dual air-bearing fixed-χ diffractometer for beamline I19 at Diamond Light Source. The diffractometer is designed to facilitate the rapid data collections possible with a Dectris Pilatus 2M pixel-array photon-counting detector, while allowing remote operation in conjunction with a robotic sample changer. The sphere-of-confusion is made as small as practicably possible, through the use of air-bearings for both the ω and φ axes. The design and construction of the new instrument is described in detail and an accompanying paper by Johnson et al. (also in this issue) will provide a user perspective of its operation.
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Nov 2017
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[12173]
Abstract: A very exceptional effect of pressure-induced dissolution has been revealed for the edible metal-organic framework γ-CD-MOF-1, formed of γ-cyclodextrin and KOH base. Also a new polymorph of γ-CD-MOF-1 has been obtained. Its trigonal structure is a symmetry subgroup modification of the cubic form. The pressure-induced dissolution of γ CD-MOF-1 and its polymorphism are closely related and regulated by adsorption in the pores as well as by the guest framework interactions.
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Feb 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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Abstract: The monotonic compression of α-D-mannose up to 9 GPa, at least, contrast with all other sugars investigated so far, undergoing a phase transition at pressure significantly lower. This exceptional stability of the α-D-mannose structure has been connected with the presence of two symmetry-independent molecules, and increased number of degrees of freedom allowing a better accommodation of strains between hydrogen-bonded molecules. Also the presence of C H∙∙∙O bonds accompanying the non-H-bonding O∙∙∙O interactions additionally stabilizes the α-D-mannose structure.
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Oct 2016
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I19-Small Molecule Single Crystal Diffraction
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Christopher H.
Woodall
,
Jeppe
Christensen
,
Jonathan M.
Skelton
,
Lauren E.
Hatcher
,
Andrew
Parlett
,
Paul R.
Raithby
,
Aron
Walsh
,
Stephen C.
Parker
,
Christine M.
Beavers
,
Simon J.
Teat
,
Mourad
Intissar
,
Christian
Reber
,
David R.
Allan
Open Access
Abstract: We report a molecular crystal that exhibits four successive phase transitions under hydrostatic pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(μ2-3,5-diisopropyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5 GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1 GPa, followed by a P21/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040 cm−1 at 2.40 GPa, decreasing steeply to 13550 cm−1 at 3 GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.
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Sep 2016
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