I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18786]
Abstract: Solid state compounds which exhibit non-centrosymmetric crystal structures are of great interest due to the physical properties they can exhibit. The ‘hybrid improper’ mechanism - in which two non-polar distortion modes couple to, and stabilize, a further polar distortion mode, yielding an acentric crystal structure - offers opportunities to prepare a range of novel non-centrosymmetric solids, but examples of compounds exhibiting acentric crystal structures stabilized by this mechanism are still relatively rare. Here we describe a series of bismuth-containing layered perovskite oxide phases, RbBiNb2O7, LiBiNb2O7 and NaBiNb2O7, which have structural frameworks compatible with hybrid-improper ferroelectricity, but also contain Bi3+ cations which are often observed to stabilize acentric crystal structures due to their 6s2 electronic configurations. Neutron powder diffraction analysis reveals that RbBiNb2O7 and LiBiNb2O7 adopt polar crystal structures (space groups I2cm and B2cm respectively), compatible with stabilization by a trilinear coupling of non-polar and polar modes. The Bi3+ cations present are observed to enhance the magnitude of the polar distortions of these phases, but are not the primary driver for the acentric structure, as evidenced by the observation that replacing the Bi3+ cations with Nd3+ cations does not change the structural symmetry of the compounds. In contrast the non-centrosymmetric, but non-polar structure of NaBiNb2O7 (space group P212121) differs significantly from the centrosymmetric structure of NaNdNb2O7, which is attributed to a second-order Jahn-Teller distortion associated with the presence of the Bi3+ cations.
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Oct 2021
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Open Access
Abstract: Luminescence probes that facilitate multimodal non-contact measurements of temperature are of particular interest due to the possibility of cross-referencing results across different readout techniques. This intrinsic referencing is an essential addition that enhances accuracy and reliability of the technique. A further enhancement of sensor performance can be achieved by using two luminescent ions acting as independent emitters, thereby adding in-built redundancy to non-contact temperature sensing, using a single readout technique. In this study we combine both approaches by engineering a material with two luminescent ions that can be independently probed through different readout modes of non-contact temperature sensing. The approach was tested using Al2O3 co-doped with Cr3+ and Mn4+, exhibiting sharp emission lines due to 2E → 4A2 transitions. The temperature sensing performance was examined by measuring three characteristics: temperature-induced changes of the intensity ratio of the emission lines, their spectral position, and the luminescence decay time constant. The processes responsible for the changes with temperature of the measured luminescence characteristics are discussed in terms of relevant models. By comparing temperature resolutions achievable by different modes of temperature sensing it is established that in Al2O3-Cr,Mn spectroscopic methods provide the best measurement accuracy over a broad temperature range. A temperature resolution better than ±2.8 K can be achieved by monitoring the luminescence intensity ratio (40–145 K) and the spectral shift of the R-line of Mn4+ (145–300 K range).
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Sep 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Open Access
Abstract: Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin) via a Zn-C / H-B exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)]- (Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzincate led to Zn-C/HBPin metathesis being the major outcome. Independent synthesis and full characterisation of two (donor)Li[(dpa)ZnPh2] (donor = 3 x THF or 1 x PMDETA) complexes, 1 and 3, respectively, enabled reactivity studies confirming these species display zincate type reactivity (by comparison to the reactivity of the neutral complex Me-NdpaZnPh2, 4). This included 1 performing the rapid deprotonation of a terminal alkyne and also phenyl transfer to α,α,α-trifluoroacetophenone in contrast to neutral complex 4. Complex 1 reacted with one equivalent of HBPin to give predominantly PhBPin (90%) and a lithium amidophenylzincate containing a hydride unit, complex 7, as the second major product. Complex 7 transfers hydride to an electrophile preferentially over phenyl, indicating it can react as a hydridozincate. Attempts to react 1 with > 1 equivalent of HBPin or with catecholborane led to more complex outcomes, which included significant borane and dpaZn substituent scrambling, two examples of which were crystallographically characterised. While this work provides proof of principle for Zn-C/H-BPin exchange as a route to form an amido-zincate containing a hydride, amido-organozincates that undergo more selective Zn-C/H-BPin exchange still are required.
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Sep 2021
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I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[18786, 20375]
Open Access
Abstract: Intercalation of lithium and ammonia into the layered semiconductor Bi2Se3 proceeds via a hyperextended (by >60%) ammonia-rich intercalate, to eventually produce a layered compound with lithium amide intercalated between the bismuth selenide layers which offers scope for further chemical manipulation.
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Aug 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[20570]
Abstract: The synthesis of six 2,6-di(pyrazol-1-yl)pyridine derivatives bearing dithiolane or carboxylic acid tether groups is described: [2,6-di(pyrazol-1-yl)pyrid-4-yl]methyl (R)-lipoate (L1), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]ethyl (R)-lipoate (L2), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxy]ethyl (R)-lipoate (L3), N-([2,6-di(pyrazol-1-yl)pyrid-4-ylsulfanyl]-2-aminoethyl (R)-lipoamide (L4), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]acetic acid (L5) and 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]propionic acid (L6). The iron(II) perchlorate complexes of all the new ligands exhibit gradual thermal spin-crossover (SCO) in the solid state above room temperature, except L4 whose complex remains predominantly high-spin. Crystalline [Fe(L6)2][ClO4]2·2MeCN contains three unique cation sites which alternate within hydrogen-bonded chains, and undergo gradual SCO at different temperatures upon warming. The SCO midpoint temperature (T1/2) of the complexes in CD3CN solution ranges between 208–274 K, depending on the functional group linking the tether groups to the pyridyl ring. This could be useful for predicting how these complexes might behave when deposited on gold or silica surfaces.
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May 2021
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I11-High Resolution Powder Diffraction
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Abstract: Recently, broad-band white-light-emitting using Eu2+, Ce3+, or Bi3+ in multi-sites of a single-phase phosphor have drawn extensive attention due to their potential to realize high-quality indoor lighting. This work reports a novel oxide Ca7Mg2Ga6O18 (CMG) possessing a complex crystal structure in the space group F432. The Rietveld refinements of high-resolution synchrotron X-ray diffraction data were performed to determine the accurate atomic positions and occupancy factors, giving a reasonable composition Ca7Mg1.91(4)Ga6.09(4)O18. Due to the multiple sites of Ca2+, which are suitable for doping of Bi3+ activators, CMG is a promising host to achieve broad-band white-light emission. Detailed structural and spectroscopic analyses revealed that the Bi3+-activator show multiple and site-selective occupancy, which is the origin of the red-shifts in both broad-band excitation and emission spectra upon increasing the Bi3+ content. A series of Bi3+ and Eu3+ codoped phosphors with tunable blue-pink-red emission were prepared due to the Bi3+-to-Eu3+ energy transfer. Distinctive thermal behaviors of Bi3+ and Eu3+ emissions make CMG:Bi3+,Eu3+a candidate to the optical thermometer.
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Apr 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[23480]
Open Access
Abstract: Gold(I) bridged dimeric and trimeric structures of a ground state spin S = 1/2 heterometallic {Cr7Ni} wheel have been prepared and studied by continuous wave (CW) and pulsed wave EPR spectrometry. The {Cr7Ni} relaxation time constants (T1 and Tm) show rates matching well with previous observations. Four pulse Double Electron Resonance (DEER) studies suggest presence of more than one conformations. Small Angle X-ray Scattering (SAXS) in conjunction with Molecular Dynamic (MD) Simulations were performed to look at the possible conformations in solution. In line with DEER results, simulation data further indicated more flexible molecular geometry in solution than the one in solid state.
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Mar 2021
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I19-Small Molecule Single Crystal Diffraction
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Juan
Angel Sans
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Francisco Javier
Manjon
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André Luis
De Jesus Pereira
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Javier
Ruiz-Fuertes
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Catalin
Popescu
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Alfonso
Muñoz
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Plácida
Rodríguez-Hernández
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Julio
Pellicer-Porres
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Vanesa Paula
Cuenca-Gotor
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Julia
Contreras-Garcia
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Jordi
Ibañez
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Virginia
Monteseguro
Diamond Proposal Number(s):
[22223]
Abstract: The structural, vibrational and electronic properties of the compressed β-Sb2O3 polymorph, a.k.a. mineral valentinite, have been investigated in a joint experimental and theoretical study up to 23 GPa. The compressibility of the lattice parameters, unit-cell volume and polyhedral unit volume as well as the behaviour of its Raman- and IR-active modes under compression have been interpreted on the basis of ab initio theoretical simulations. Valentinite shows an unusual compressibility up to 15 GPa with four different pressure ranges, whose critical pressures are 2, 4, and 10 GPa. The pressure dependence of the main structural units, the lack of soft phonons, and the electronic density charge topology address the changes at those critical pressures to isostructural phase transitions of degree higher than 2. In particular, the transitions at 2 and 4 GPa can be ascribed to the changes in the interaction between the stereochemically-active lone electron pairs of Sb atoms under compression. The changes observed above 10 GPa, characterized by a general softening of several Raman- and IR-active modes, point to a structural instability prior to the 1st-order transition occurring above 15 GPa. Above this pressure, a tentative new high-pressure phase (s.g. Pcc2) has been assigned by single-crystal and powder X-ray diffraction measurements.
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Mar 2021
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E02-JEM ARM 300CF
I15-1-X-ray Pair Distribution Function (XPDF)
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Adam F.
Sapnik
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Duncan N.
Johnstone
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Sean M.
Collins
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Giorgio
Divitini
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Alice M.
Bumstead
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Christopher W.
Ashling
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Philip A.
Chater
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Dean S.
Keeble
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Timothy
Johnson
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David A.
Keen
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Thomas D.
Bennett
Diamond Proposal Number(s):
[20038, 20198]
Open Access
Abstract: Defect engineering is a powerful tool that can be used to tailor the properties of metal–organic frameworks (MOFs). Here, we incorporate defects through ball milling to systematically vary the porosity of the giant pore MOF, MIL-100 (Fe). We show that milling leads to the breaking of metal–linker bonds, generating additional coordinatively unsaturated metal sites, and ultimately causes amorphisation. Pair distribution function analysis shows the hierarchical local structure is partially retained, even in the amorphised material. We find that solvents can be used to stabilise the MIL-100 (Fe) framework against collapse, which leads to a substantial retention of porosity over the non-stabilised material.
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Mar 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6302]
Abstract: The reaction between two equivalents of {(Me3Si)2CH}(Ph)PH(BH3) (1) and Bu2Mg, followed by two
equivalents of BH3·SMe2, gives the corresponding phosphido-bis(borane) complex, which may be crystallised as two distinct chemical species: the complex [{(Me3Si)2CH}(Ph)P(BH3)2]2Mg(THF)4·THF (2a), and two
different THF solvates (1 : 1 and 1 : 2) of the solvent-separated ion triples [{(Me3Si)2CH}(Ph)P(BH3)2]2[Mg
(THF)6]·THF (2b) and [{(Me3Si)2CH}(Ph)P(BH3)2]2[Mg(THF)6]·2THF (2c). Similar reactions between two
equivalents of 1 and either (4-tBuC6H4CH2)2Ca(THF)4 or [(Me3Si)2CH]2Sr(THF)2, followed by two equivalents of BH3·SMe2, give the heavier alkali metal complexes [{(Me3Si)2CH}(Ph)P(BH3)2]2M(THF)4 [M = Ca (3),
Sr (4)]. Surprisingly, compounds 2a, 3 and 4 adopt almost identical structures in the solid state, which
differ only in the geometrical arrangement of the phosphido-bis(borane) ligands and the hapticity of the
borane groups.
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Dec 2020
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