I15-Extreme Conditions
|
Diamond Proposal Number(s):
[30815]
Open Access
Abstract: Molecular perovskites are important materials in the area of barocalorics, improper ferroelectrics and ferroelastics, where the search for principles that link composition, structure and mechanical properties is a key challenge. Herein, we report the synthesis of a new series of dicyanamide-based molecular perovskites [A]Ni(C2N3)3, where the A-site cation (A+) is a range of alkylated piperidinium cations. We use this new family to explore how A+ cations determine their mechanical response by measuring the bulk modulus (B) – using high-pressure powder X-ray diffraction. Within the series, we find a positive correlation between the network distortions of the pseudocubic [Ni(C2N3)3]− network and B. Furthermore, we show that we can tune framework distortions, and therefore B, by synthesising A-site solid solutions. The applied methodology is a blueprint for linking framework distortions and mechanical properties in network materials and guides us toward principles for designing macroscopic properties via systematic compositional changes in molecular perovskites.
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Jul 2024
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I15-Extreme Conditions
|
Silva M.
Kronawitter
,
Richard
Röß-Ohlenroth
,
Sebastian A.
Hallweger
,
Marcel
Hirrle
,
Hans Albrecht
Krug
,
Tobias
Luxenhofer
,
Emily
Myatt
,
Jem
Pitcairn
,
Matthew J.
Cliffe
,
Dominik
Daisenberger
,
Jakub
Wojciechowski
,
Dirk
Volkmer
,
Gregor
Kieslich
Diamond Proposal Number(s):
[30815]
Open Access
Abstract: Fe(II)-containing Metal-Organic Frameworks (MOFs) that exhibit temperature-induced spin-crossover (SCO) are candidate materials in the field of sensing, barocalorics, and data storage. Their responsiveness towards pressure is therefore of practical importance and is related to their longevity and processibility. The impact of Fe(II) spin-state on the pressure responsiveness of MOFs is yet unexplored. Here we report the synthesis of two new Fe(II)-based MOFs, i.e. Fe(cta)2 ((cta)– = 1,4,5,6-tetrahydrocyclopenta[d][1,2,3]triazolate) and Fe(mta)2 ((mta)– = methyl[1,2,3]triazolate), which are both in high-spin at room temperature. Together with the isostructural MOF Fe(ta)2 ((ta)– = [1,2,3]triazolate), which is in its low-spin state at room temperature, we apply these as model systems to show how spin-state controls their mechanical properties. As a proxy, we use their bulk modulus, which was obtained via high-pressure powder X-ray diffraction experiments. We find that an interplay of spin-state, steric effects, void fraction, and absence of available distortion modes dictates their pressure-induced structural distortions. Our results show for the first time the role of spin-state on the pressure-induced structural deformations in MOFs and bring us a step closer to estimating the effect of pressure as a stimulus on MOFs a priori.
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Feb 2024
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I15-Extreme Conditions
|
Madeleine
Geers
,
David M.
Jarvis
,
Cheng
Liu
,
Siddharth S.
Saxena
,
Jem
Pitcairn
,
Emily
Myatt
,
Sebastian A.
Hallweger
,
Silva M.
Kronawitter
,
Gregor
Kieslich
,
Sanliang
Ling
,
Andrew B.
Cairns
,
Dominik
Daisenberger
,
Oscar
Fabelo
,
Laura
Cañadillas-Delgado
,
Matthew J.
Cliffe
Diamond Proposal Number(s):
[30815]
Open Access
Abstract: Two-dimensional materials offer a unique range of magnetic, electronic, and mechanical properties which can be controlled by external stimuli. Pressure is a particularly important stimulus, as it can be achieved readily and can produce large responses, especially in low-dimensional materials. In this paper, we explore the pressure dependence of the structural and magnetic properties of a two-dimensional van der Waals (vdW) molecular framework antiferromagnet with ferromagnetic layers,
Ni
(
NCS
)
2
, up to 8.4 kbar. Through a combination of x-ray and neutron diffraction analysis, we find that
Ni
(
NCS
)
2
is significantly more compressible than comparable vdW metal halides, and its response is anisotropic not only out of the plane, but also within the layers. Using bulk magnetization and neutron diffraction data, we show that the ambient layered antiferromagnetic phase is maintained up to the largest investigated pressure, but with an enhanced Néel temperature,
T
N
(
Δ
T
N
/
T
N
=
+
19
%
), and a large pressure sensitivity (
Q
=
1
T
N
d
T
N
d
P
=
+
2.3
%
kbar
−
1
), one of the larger values of magnetic pressure responsiveness for a vdW material. Density functional theory calculations suggest that this is due to increasing three dimensionality. These results provide insights into the pressure response of molecular framework vdW magnets and suggest that the investigation of other molecular framework vdW magnets might uncover contenders for future pressure-switchable devices.
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Oct 2023
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
|
Diamond Proposal Number(s):
[17773, 24447]
Open Access
Abstract: Understanding the factors that underpin the enormous catalytic proficiencies of enzymes is fundamental to catalysis and enzyme design. Enzymes are, in part, able to achieve high catalytic proficiencies by utilizing the binding energy derived from nonreacting portions of the substrate. In particular, enzymes with substrates containing a nonreacting phosphodianion group coordinated in a distal site have been suggested to exploit this binding energy primarily to facilitate a conformational change from an open inactive form to a closed active form, rather than to either induce ground state destabilization or stabilize the transition state. However, detailed structural evidence for the model is limited. Here, we use β-phosphoglucomutase (βPGM) to investigate the relationship between binding a phosphodianion group in a distal site, the adoption of a closed enzyme form, and catalytic proficiency. βPGM catalyzes the isomerization of β-glucose 1-phosphate to glucose 6-phosphate via phosphoryl transfer reactions in the proximal site, while coordinating a phosphodianion group of the substrate(s) in a distal site. βPGM has one of the largest catalytic proficiencies measured and undergoes significant domain closure during its catalytic cycle. We find that side chain substitution at the distal site results in decreased substrate binding that destabilizes the closed active form but is not sufficient to preclude the adoption of a fully closed, near-transition state conformation. Furthermore, we reveal that binding of a phosphodianion group in the distal site stimulates domain closure even in the absence of a transferring phosphoryl group in the proximal site, explaining the previously reported β-glucose 1-phosphate inhibition. Finally, our results support a trend whereby enzymes with high catalytic proficiencies involving phosphorylated substrates exhibit a greater requirement to stabilize the closed active form.
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Feb 2022
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B18-Core EXAFS
E01-JEM ARM 200CF
|
Emerson Cristofer
Kohlrausch
,
Higor A.
Centurion
,
Rhys
Lodge
,
Xuanli
Luo
,
Thomas
Slater
,
Marcos J. L.
Santos
,
Sanliang
Ling
,
Valmor R.
Mastelaro
,
Matthew J.
Cliffe
,
Renato
Vitalino Goncalves
,
Jesum
Alves Fernandes
Diamond Proposal Number(s):
[25120, 17198, 24914]
Open Access
Abstract: Atomically-dispersed metal catalysts (ADMCs) on surfaces have demonstrated
high activity and selectivity in many catalytic reactions. However, dispersing and stabilising
individual atoms in support materials in an atom/energy-efficient scalable way still presents a
significant challenge. Currently, the synthesis of ADMCs involves many steps and further
filtration procedures, creating a substantial hurdle to their production at industrial scale. In this
work, we develop a new pathway for producing ADMCs in which Pt atoms are stabilised in the
nitrogen-interstices of a graphitic carbon nitride (g-C3N4) framework using scalable, solvent-free,
one-pot magnetron sputtering deposition. Our approach has the highest reported rate of ADMC
production of 4.8 mg h-1 and generates no chemical waste. Deposition of only 0.5 weight percent
of Pt onto g-C3N4 led to improved hydrogen production by factor of ca. 3333 ± 450 when compared to bare g-C3N4. PL analysis showed that the deposition of Pt atoms onto g-C3N4 suppressed the
charge carrier recombination from the photogenerated electron-hole pairs of Pt/g-C3N4 thereby
enhance hydrogen evolution. Scanning transmission electron microscope imaging before and after
the hydrogen evolution reaction revealed that the Pt atoms stabilised in g-C3N4 have a high
stability, with no agglomeration observed. Herein, it is shown that this scalable and clean approach
can produce effective ADMCs with no further synthetic steps required, and that they can be readily
used for catalytic reactions.
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Nov 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[18630]
Open Access
Abstract: The structures of Zr and Hf metal–organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.
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Nov 2021
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I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[21755, 8786]
Open Access
Abstract: We report four new A-site vacancy ordered thiocyanate double double perovskites,A1–x{Ni[Bi(SCN)6](1–x)/3}, A = K+, NH4+, CH3(NH3)+ (MeNH3+) and C(NH2)3+ (Gua+), includingthe first examples of thiocyanate perovskites containing organic A-site cations. We show, usinga combination of X-ray and neutron diffraction, that the structure of these frameworks dependson the A-site cation, and that these frameworks possess complex vacancy-ordering patterns andcooperative octahedral tilts distinctly different from atomic perovskites. Density functional theorycalculations uncover the energetic origin of these complex orders and allow us to propose asimple rule to predict favoured A-site cation orderings for a given tilt sequence. We use theseinsights, in combination with symmetry mode analyses, to show that these complex orders offera new route to non-centrosymmetric perovskites which render them as excellent candidates forpiezo- and ferroelectric applications.
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Jan 2021
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E02-JEM ARM 300CF
|
Diamond Proposal Number(s):
[20195, 21979, 20198]
Abstract: Defect engineering can enhance key properties of metal-organic frameworks (MOFs). Tailoring the distribution of de-fects, for example in correlated nanodomains, requires characterization across length scales. However, a critical na-noscale characterization gap has emerged between the bulk diffraction techniques used to detect defect nanodomains and the sub-nanometer imaging used to observe individual defects. Here, we demonstrate that the emerging technique of scanning electron diffraction (SED) can bridge this gap uniquely enabling both nanoscale crystallographic analysis and the low-dose formation of multiple diffraction contrast images for defect analysis in MOFs. We directly image defect nanodomains in the MOF UiO-66(Hf) over an area of ca. 1 000 nm and with a spatial resolution ca. 5 nm to reveal domain morphology and distribution. Based on these observations, we suggest possible crystal growth processes underpinning synthetic control of defect nanodomains. We also identify likely dislocations and small angle grain boundaries, illustrating that SED could be a key technique in developing the potential for engineering the distribution of defects, or “microstruc-ture”, in functional MOF design.
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Jul 2020
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I19-Small Molecule Single Crystal Diffraction
|
Abstract: A series of symmetrically bis‐4‐methoxybenzyl (4MB) N‐substituted 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP) derivatives have been synthesized. The 4MB unit makes the DPP core soluble, and shows subtle modification of up to 0.2 eV in ground and excited states of the core when compared with related alkyl derivatives. Absorption and emission spectroscopy, as well as electrochemical and computational methods have been employed to prove the importance of the peripheral aryl units on the donor/ acceptor properties of the molecules. The 4MB products are highly fluorescent (quantum yields approaching 100 % in solution), with a unique distribution of frontier states shown by spectroelectrochemistry. The solid‐state fluorescence correlates with the X‐ray crystal structures of the compounds, a Stokes shift of approximately 80 nm is seen for two of the compounds. The frontier energy levels show that this subtle substitutional change could be of future use in molecular energy level tailoring in these, and related, materials for organic (opto)electronics.
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Jul 2019
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I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[15118]
Open Access
Abstract: We report the first examples of thiocyanate-based analogues of the cyanide Prussian blue compounds, MIII[Bi(SCN)6], M = Fe, Cr, Sc. These compounds adopt the primitive cubic pcu topology and show strict cation order. Optical absorption measurements show these compounds have band gaps within the visible and near IR region, suggesting that they may be useful for applications where light harvesting is key, such as photocatalysis. We also show that Cr[Bi(SCN)6] can reversibly uptake water into its framework structure pointing towards the possibility of using these frameworks for host/guest chemistry.
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Oct 2018
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