I15-Extreme Conditions
|
Diamond Proposal Number(s):
[29285]
Open Access
Abstract: Rutile-structured materials can exhibit negative linear compressibility (NLC) following ferroelastic phase transitions, expanding in one direction under uniform compression. We investigate this phenomenon in structural analogues—transition metal dicyanamides (dca) and tricyanomethanides (tcm) with single and double rutile-like structures, respectively. The pressure-induced structural behaviour of Cu(tcm)2 and Cu(dca)2 are studied using high-pressure diffraction. Both systems undergo anisotropic deformation upon compression, with Cu(dca)2 exhibiting NLC of −6.5(10) TPa−1 along the c-axis, while Cu(tcm)2 shows zero linear compressibility (ZLC) along the a-axis. This difference is attributed to the single rutile-like network with flexible dca− linkers in Cu(dca)2, in contrast to the more constrained doubly interpenetrating structure of Cu(tcm)2 with rigid tcm− linkers. We also study the interplay between structural features and electronic effects arising from the Jahn–Teller distortion in both materials, in controlling their compression behaviour.
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Dec 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[29285]
Open Access
Abstract: Copper(I) tricyanomethanide, Cu(tcm), is a flexible framework material that exhibits the strongest negative area compressibility (NAC) effect ever observed─a remarkable property with potential applications in pressure sensors, artificial muscles, and shock-absorbing devices. Under increasing pressure, Cu(tcm) undergoes two sequential phase transitions (tetragonal → orthorhombic → monoclinic): It has an initial tetragonal structure (I41md) at ambient conditions, but this structure only persists within a narrow pressure range; at 0.12(3) GPa, a pressure-induced ferroelastic phase transition occurs, transforming Cu(tcm) into a low-symmetry orthorhombic structure (Fdd2). The orthorhombic phase has a NAC of −108(14) TPa–1 in the b–c plane between 0.12(3) and 0.93(8) GPa. The NAC behavior is associated with framework hinge motion in a flexible framework with “wine-rack” topology. At 0.93(8) GPa, Cu(tcm) undergoes a second phase transition and transforms into a layered monoclinic structure (Cc) with topologically interpenetrating honeycomb networks. The monoclinic phase of Cu(tcm) exhibits a slight negative linear compressibility (NLC) of −1.1(1) TPa–1 along the a axis and a zero area compressibility of Kac = Ka + Kc = 0.0(4) TPa–1 in the a–c plane over the pressure range of 0.93–2.63 GPa. In contrast to the orthorhombic phase, its mechanism is understood as the pressure-driven dampening of layer “rippling,” which acts to increase the cross-sectional area of the layer at higher hydrostatic pressures. These findings have implications for understanding the underlying mechanism of NAC phenomenon in framework materials.
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May 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18324]
Open Access
Abstract: With the advent of ever more intense and focused X-ray sources, including in laboratories, at synchrotrons, and at X-ray free electron lasers, radiation-induced sample change and damage are becoming increasingly challenging. Therefore, the exploration of possible mitigation strategies is crucial to continue to allow the collection of robust and repeatable data. One mitigation approach is the introduction of short, X-ray-free “dark” periods. However, it is unclear whether this strategy minimises damage or, in actuality, promotes it through a phenomenon called “dark progression”, i.e. the increase or progression of radiation damage that occurs after the X-ray beam is turned off. This work discusses the influence of introducing dark periods and their duration on the radiation-induced changes in two model small-molecule catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to X-ray radiation in synchrotron powder diffraction (PXRD) and laboratory photoelectron spectroscopy (XPS) experiments. This provides, for the first time, insights into how damage progresses under varying radiation regimes and allows the distinction between the processes that affect the unit cell itself, the individual molecular units, and the respective atomic chemical environments. Furthermore, it provides the basis for informed decision-making in the design of future experiments where the need to minimise radiation-induced damage is crucial.
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Apr 2025
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[32115]
Open Access
Abstract: Extended framework materials with specific topologies can exhibit unusual mechanical behaviour, such as expanding in one direction under hydrostatic (uniform) pressure, known as negative linear compressibility (NLC). Here, two hybrid perovskite frameworks with winerack structures, a known NLC topology, are investigated under pressure. [C(NH2)3]Er(HCO2)2(C2O4) exhibits NLC from ambient pressure to 2.63(10) GPa, the first reported NLC hybrid perovskite from ambient pressure. However, isostructural [(CH3)2NH2]Er(HCO2)2(C2O4) instead compresses relatively moderately along all axes before it undergoes a phase transition above 0.37(10) GPa. The differences in the mechanical properties can be interpreted from differences in host–guest interactions within these frameworks, primarily their hydrogen bond networks.
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Feb 2024
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[30164, 30055]
Open Access
Abstract: Jahn–Teller (JT) distorted CuII-containing compounds often display interesting structural and functional behaviour upon compression. We use high-pressure X-ray and neutron diffraction to investigate four JT-distorted Prussian blue analogues: Cu[Co(CN)6]0.67, CuPt(CN)6, and ACuCo(CN)6 (A = Rb, Cs), where the first two were studied in both their hydrated and dehydrated forms. All compounds are less compressible than the JT-inactive MnII-based counterparts, indicating a coupling between the electronic and mechanical properties. The effect is particularly strong for Cu[Co(CN)6]0.67, where the local JT distortions are uncorrelated (so-called orbital disorder). This sample amorphises at 0.5 GPa when dehydrated. CuPt(CN)6 behaves similarly to the MnII-analogues, with phase transitions at around 1 GPa and low sensitivity to water. For ACuCo(CN)6, the JT distortions reduce the propensity for phase transitions, although RbCuCo(CN)6 transitions to a new phase (P2/m) around 3 GPa. Our results have a bearing on both the topical Prussian blue analogues and the wider field of flexible frameworks.
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Jan 2024
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I15-Extreme Conditions
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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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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[23209]
Open Access
Abstract: X-ray characterisation methods have undoubtedly enabled cutting-edge advances in all aspects of materials research. Despite the enormous breadth of information that can be extracted from these techniques, the challenge of radiation-induced sample change and damage remains prevalent. This is largely due to the emergence of modern, high-intensity X-ray source technologies and the growing potential to carry out more complex, longer duration in situ or in operando studies. The tunability of synchrotron beamlines enables the routine application of photon energy-dependent experiments. This work explores the structural stability of [Rh(COD)Cl]2, a widely used catalyst and precursor in the chemical industry, across a range of beamline parameters that target X-ray energies of 8 keV, 15 keV, 18 keV and 25 keV, on a powder X-ray diffraction synchrotron beamline at room temperature. Structural changes are discussed with respect to absorbed X-ray dose at each experimental setting associated with the respective photon energy. In addition, the X-ray radiation hardness of the catalyst is discussed, by utilising the diffraction data collected at the different energies to determine a dose limit, which is often considered in protein crystallography and typically overlooked in small molecule crystallography. This work not only gives fundamental insight into how damage manifests in this organometallic catalyst, but will encourage careful consideration of experimental X-ray parameters before conducting diffraction on similar radiation-sensitive organometallic materials.
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Nov 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[30164]
Open Access
Abstract: The Prussian blue analogue CsMnCo(CN)6 is studied using powder X-ray and neutron diffraction under variable temperature, pressure, and X-ray dose. It retains the cubic $F\bar{4}3m$ symmetry in the range 85--500 K with minimal thermal expansion, whereas a phase transition to $P\bar{4}n2$ occurs at ∼2 GPa, driven by octahedral tilting. A small lattice contraction occurs upon increased X-ray exposure. Comparisons with related systems indicate that the CsI ions decrease the thermal expansion and suppresses the likelihood of phase transformation. The results increase the understanding of the stimuli-responsive behaviour of coordination polymers.
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Oct 2022
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I11-High Resolution Powder Diffraction
I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[19420, 22705]
Abstract: X-ray characterization techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray-induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever-increasing brilliance are developed. In this paper, systematic studies of X-ray–matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complementary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray-induced effects in transition-metal catalysts and, consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.
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Aug 2021
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[19776]
Open Access
Abstract: The vast compositional space of Prussian blue analogues (PBAs), formula AxM[M′(CN)6]y·nH2O, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties—e.g., flexibility and propensity for phase transitions—is still largely unknown, despite its fundamental and industrial relevance. Here we use variable-pressure X-ray and neutron diffraction to explore how key structural features, i.e., defects, hydration, and composition, influence the compressibility and phase behavior of PBAs. Defects enhance the flexibility, manifesting as a remarkably low bulk modulus (B0 ≈ 6 GPa) for defective PBAs. Interstitial water increases B0 and enables a pressure-induced phase transition in defective systems. Conversely, hydration does not alter the compressibility of stoichiometric MnPt(CN)6, but changes the high-pressure phase transitions, suggesting an interplay between low-energy distortions. AMnCo(CN)6 (AI = Rb, Cs) transition from F4̅3m to P4̅n2 upon compression due to octahedral tilting, and the critical pressure can be tuned by the A-site cation. At 1 GPa, the symmetry of Rb0.87Mn[Co(CN)6]0.91 is further lowered to the polar space group Pn by an improper ferroelectric mechanism. These fundamental insights aim to facilitate the rational design of PBAs for applications within a wide range of fields.
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Feb 2021
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