High-pressure Single-crystal X-ray Diffraction Research Articles

Halogen⋯halogen contra C–H⋯halogen interactions

Pressure affects the competition between C–H⋯X hydrogen bonds and X⋯X halogen⋯halogen interactions. In bromomethane, CH3Br, pressure changes the molecular arrangement of the two solid-state phases of this compound: low-pressure phase α is dominated by halogen⋯halogen interactions, whereas above 1.5 GPa the β phase is governed by C–H⋯halogen bonds. The CH3Br phase α is isostructural with solid CH3I of orthorhombic space group Pnma, while CH3Br phase β is polar, isostructural with CH3Cl and CH3CN crystals, of orthorhombic space group Cmc21. The crystal structures of CH3Cl (b.p. = 249.1 K) and CH3Br (b.p. = 276.7 K) have been determined by high pressure single-crystal X-ray diffraction up to 4.38 GPa and 2.85 GPa, respectively. In CH3Br, pressure of 1.5 GPa enforces the close packing and opposite electrostatic-potential matching between molecular surfaces in contact. The interweaved C–H⋯X bonded diamondoid networks of β-CH3X are similar to those of acetonitrile, H2O ice VII and solidified X2 halogens. The phase diagrams of CH3Br and CH3Cl have been constructed.

Hingeless negative linear compression in the mechanochromic gold complex [(C6F5Au)2(μ-1,4-diisocyanobenzene)

The compression of a crystalline material under hydrostatic pressure always results in a reduction in volume of the solid, with the observed reduction typically occurring in all crystallographic cell parameters.1 However, there are a number of exceptional materials that have been shown to expand in a specific direction upon hydrostatic compression while maintaining a positive volume compression. The phenomenon of uni-or biaxial expansion under compression is known as negative linear compressibility (NLC).1 Rare examples of NLC have attracted attention recently owing to the potential applications in a range of materials, including body armor, artificial muscle actuators, and pressure sensors.2

Distinct Responses to Mechanical Grinding and Hydrostatic Pressure in Luminescent Chromism of Tetrathiazolylthiophene

Luminescent mechanochromism has been intensively studied in the past few years. However, the difference in the anisotropic grinding and the isotropic compression is not clearly distinguished in many cases, in spite of the importance of this discrimination for the application of such mechanochromic materials. We now report the distinct luminescent responses of a new organic fluorophore, tetrathiazolylthiophene, to these stresses. The multichromism is achieved over the entire visible region using the single fluorophore. The different mechanisms of a blue shift by grinding crystals and of a red shift under hydrostatic pressure are fully investigated, which includes a high-pressure single-crystal X-ray diffraction analysis. The anisotropic and isotropic modes of mechanical loading suppress and enhance the excimer formation, respectively, in the 3D hydrogen-bond network.

High pressure single-crystal micro X-ray diffraction analysis with GSE_ADA/RSV software

GSE_ADA/RSV is a free software package for custom analysis of single-crystal micro X-ray diffraction (SCμXRD) data, developed with particular emphasis on data from samples enclosed in diamond anvil cells and subject to high pressure conditions. The package has been in extensive use at the high pressure beamlines of Advanced Photon Source (APS), Argonne National Laboratory and Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. The software is optimized for processing of wide-rotation images and includes a variety of peak intensity corrections and peak filtering features, which are custom-designed to make processing of high pressure SCμXRD easier and more reliable.

The influence of pressure on the photoluminescence properties of a terbium-adipate framework

The influence of pressure (over the 0–4.7 GPa range) on the photoluminescence emissions and crystal structure of the known 3D terbium-adipate metal-organic framework material Tb-GWMOF6 has been evaluated by high-pressure single-crystal X-ray diffraction and spectroscopic techniques. The results from this study show that this complex lanthanide framework structure undergoes three phase transitions within the 0–4 GPa pressure range that involve alterations in the number of symmetry independent Tb3+ ion sites within the crystal lattice. These pressure induced modifications to the structure of Tb-GWMOF6 lead to pronounced changes in the profiles of the 5D4→7F5 emission spectra of this complex.

High-pressure X-ray study of LiCrSi2O6 clinopyroxene and the general compressibility trends for Li-clinopyroxenes

High-pressure single-crystal X-ray diffraction measurements of synthetic LiCrSi2O6 clinopyroxene (with space group P21/c) were performed in a diamond-anvil cell up to 7.970 GPa. No phase transition has been observed within the pressure range investigated, but the elastic behavior at lower pressures (up to ~2.5 GPa) is affected by an anomalous softening due to the proximity of the phase transition to the HT-C2/c phase at 330 K and at ambient pressure. A third-order Birch–Murnaghan equation of state fitted to the compression data above 2.5 GPa yields a bulk modulus K T0 = 93(2) GPa and its first derivative K′ = 8.8(6). The structural data measured up to 7.970 GPa confirm that the space group P21/c is maintained throughout the whole pressure range investigated. The atomic parameters, obtained from the integrated diffraction intensities, suggest that the Li coordination polyhedron changes its coordination number from 5 to 6 at 6–7 GPa by means of the approach of the bridging O atom, related to the increased kinking of the B tetrahedral chain. Furthermore, at higher pressures, the structural evolution of LiCrSi2O6 provides evidence in the variation of kinking angles and bond lengths of a potential phase transition above 8 GPa to the HP-C2/c space group. A comparison of the Li-clinopyroxenes (M1 = Cr, Al, Sc, Ga, Mg + Fe) previously investigated and our sample shows that their elastic behavior and structural mechanisms of compression are analogous.

Portable double-sided laser-heating system for Mössbauer spectroscopy and X-ray diffraction experiments at synchrotron facilities with diamond anvil cells

The diamond anvil cell (DAC) technique coupled with laser heating is a major method for studying materials statically at multimegabar pressures and at high temperatures. Recent progress in experimental techniques, especially in high-pressure single crystal X-ray diffraction, requires portable laser heating systems which are able to heat and move the DAC during data collection. We have developed a double-sided laser heating system for DACs which can be mounted within a rather small (~0.1 m(2)) area and has a weight of ~12 kg. The system is easily transferable between different in-house or synchrotron facilities and can be assembled and set up within a few hours. The system was successfully tested at the High Pressure Station of White Beam (ID09a) and Nuclear Resonance (ID18) beamlines of the European Synchrotron Radiation Facility. We demonstrate examples of application of the system to a single crystal X-ray diffraction investigation of (Mg(0.87),Fe(3+) (0.09),Fe(2+) (0.04))(Si(0.89),Al(0.11))O(3) perovskite (ID09a) and a Synchrotron Mössbauer Source (SMS) study of (Mg(0.8)Fe(0.2))O ferropericlase (ID18).

Pressure versus Temperature Effects on Intramolecular Electron Transfer in Mixed‐Valence Complexes

Mixed-valence trinuclear carboxylates, [M(3)O(O(2)CR)(6)L(3)] (M = metal, L = terminal ligand), have small differences in potential energy between the configurations M(II)M(III)M(III)⇔M(III)M(II)M(III)⇔M(III)M(III)M(II), which means that small external changes can have large structural effects, owing to the differences in coordination geometry between M(2+) and M(3+) sites (e.g., about 0.2 Å for Fe-O bond lengths). It is well-established that the electron transfer (ET) between the metal sites in these mixed-valence molecules is strongly dependent on temperature and on the specific crystal environment; however, herein, for the first time, we examine the effect of pressure on the electron transfer. Based on single-crystal X-ray diffraction data that were measured at 15, 90, 100, 110, 130, 160, and 298 K on three different crystals, we first unexpectedly found that our batch of Fe(3)O (O(2)CC(CH(3))(3))(6)(C(5)H(5)N)(3) (1) exhibited a different temperature dependence of the ET process than previous studies of compound 1 have shown. We observed a phase transition at around 130 K that was related to complete valence trapping and Hirshfeld surface analysis revealed that this phase transition was governed by a subtle competition between C-H⋅⋅⋅π and π⋅⋅⋅π intermolecular interactions. Subsequent high-pressure single-crystal X-ray diffraction at pressures of 0.15, 0.35, 0.45, 0.74, and 0.96 GPa revealed that it was not possible to trigger the phase transition (i.e., valence trapping) by a reduction of the unit-cell volume, owing to this external pressure. We conclude that modulation of the ET process requires anisotropic changes in the intermolecular interactions, which occur when various directional chemical bonds are affected differently by changes in temperature, but not by the application of pressure.

On the high-pressure behavior of gobbinsite, the natural counterpart of the synthetic zeolite Na–P2

An in situ high-pressure single-crystal X-ray diffraction study of gobbinsite, the natural counterpart of the synthetic zeolite Na–P2, was carried out up to 4.3GPa. No evidence of amorphization was observed within pressure-range investigated. Using a non-penetrating P-medium, two changes of the elastic behavior occur: the first at 1.1–1.3GPa and the second at 2.7–3.2GPa. Birch-Murnaghan equations of state truncated to the second order were used to fit the experimental P–V data within the three P-ranges (i.e. 0.0001–1.1, 1.3–2.7 and 3.2–4.3GPa), giving the following isothermal bulk moduli (KV0): 46.3(9), 52(8) and 28(6) GPa, respectively. The unit-cell compression is significantly anisotropic. In response to the applied pressure, the 8-membered ring channel parallel to [100] undergoes a significant increase of ellipticity, whereas the channel parallel to [010] undergoes a shrinking towards a circular shape at P≥1.3GPa. A partial re-organization of the H2O sites occurs between 1.1 and 1.3GPa, and new framework deformational modes onset at P≥3.2GPa, coupled with a change in the coordination environment of the extraframework cations.

Negative Linear Compressibility of a Metal–Organic Framework

A 3D hybrid zinc formate framework, [NH(4)][Zn(HCOO)(3)], possessing an acs topology, shows a high degree of mechanical anisotropy and negative linear compressibility (NLC) along its c axis. High-pressure single-crystal X-ray diffraction studies and density functional theory calculations indicate that contraction of the Zn-O bonds and tilting of the formate ligands with increasing pressure induce changes in structure that result in shrinkage of the a and b axes and the NLC effect along c.

High-pressure behavior of zoisite

A high-pressure single-crystal X-ray diffraction (XRD) study has been carried out on two natural zoisite samples Ca 2 Al 3-x FexSi 3 O 12 OH, one Fe-free (x = 0) and one Fe-rich (x = 0.12). The unit-cell parameters were determined for the Fe-free sample at 18 different pressures up to 7.76 GPa and for the Fe-rich sample at 13 different pressures up to 7.63 GPa. The P(V) data for both of the samples were fitted by a third-order Birch-Murnaghan equation of state (BM3 EoS). The equation of state coefficients are: V 0 = 903.39(5) Å 3 , K T0 = 122.1(7) GPa, and K 0 ′ = 6.8(2) for the Fe-free sample and V 0 = 906.95(5) Å 3 , K T0 = 119.1(7) GPa, and K 0 ′ = 7.3(2) for the Fe-rich sample. This shows that the addition of Fe in to the crystal structure of zoisite leads to a slight softening of the structure. Both compositions exhibit axial compressibilities β c > β a >> β b , with the compressibilities of the a and b axes of the two samples being indistinguishable. The softening of the bulk modulus of zoisite with Fe content follows from softening of the c-axis of the structure. A high-pressure structural study of the Fe-free sample showed that the main compression mechanisms in the structure are the compression of soft inter-octahedral distance along [001] and soft intra-octahedral distances along [010] directions, while along [100] the main compression occurs because of the compression of stiff intra-octahedral distances. The substitution of Fe on to the M3 octahedral site of the structure leads to an increase of the intra-octahedral distance of the M3 that triggers the rotation of M12 and therefore leads to the softening of the M12 inter-octahedral distances that accounts for the softening of the c-axis of the structure.

Compressibility of NaMnSi2O6: The role of electronic isovalency for the validity of bulk-modulus–volume relationship

A natural crystal with NaMnSi2O6 composition (space group C2/c) belonging to the family of clinopyroxene structures was investigated by in-situ high-pressure single-crystal X-ray diffraction up to 9 GPa in order to verify if the compressibility can be predicted from the unit-cell volume V0 at 1 bar applying an established volume–compressibility relationship. Together with data for isostructural analogue phases the equation-of-state parameters of NaMnSi2O6 showed that such simplified relationship can not be longer applied. The findings demonstrate that prediction models for isostructural series are consistent not only for the aspect of structural isotopy, and valid relationships presuppose similar character of the electronic structure. In case of pyroxenes containing transition elements the established relationship is only valid for series of compounds with cations of identical oxidation state according to isovalent electronic character.

Effect of high pressure on the crystal structure and electronic properties of magnetite below 25 GPa

We report results from high-pressure single-crystal X-ray diffraction and Mössbauer absorption experiments on magnetite. Based on high-quality diffraction data, we have obtained accurate information on the crystal structure of magnetite below 25 GPa, which enables an unambiguous interpretation of the Mössbauer data using constrained area ratios and a full transmission integral fit that avoids area distortion due to thickness effects. Based on our analysis, all aspects of the electronic and magnetic properties of magnetite reported previously below 25 GPa at ambient temperature can be explained solely by the enhanced delocalization of 3d electrons of iron atoms. For instance, we present evidence that the compression-induced metallization changes the sign of the charge carrier spin polarization at 15 GPa.

High-pressure crystal structure of elastically isotropic CaTiO3 perovskite under hydrostatic and non-hydrostatic conditions

The structural evolution of orthorhombic CaTiO3 perovskite has been studied using high-pressure single-crystal x-ray diffraction under hydrostatic conditions up to 8.1 GPa and under a non-hydrostatic stress field formed in a diamond anvil cell (DAC) up to 4.7 GPa. Under hydrostatic conditions, the TiO6 octahedra become more tilted and distorted with increasing pressure, similar to other 2:4 perovskites. Under non-hydrostatic conditions, the experiments do not show any apparent difference in the internal structural variation from hydrostatic conditions and no additional tilts and distortions in the TiO6 octahedra are observed, even though the lattice itself becomes distorted due to the non-hydrostatic stress. The similarity between the hydrostatic and non-hydrostatic cases can be ascribed to the fact that CaTiO3 perovskite is nearly elastically isotropic and, as a consequence, its deviatoric unit-cell volume strain produced by the non-hydrostatic stress is very small; in other words, the additional octahedral tilts relevant to the extra unit-cell volume associated with the deviatoric unit-cell volume strain may be totally neglected. This study further addresses the role that three factors—the elastic properties, the crystal orientation and the pressure medium—have on the structural evolution of an orthorhombic perovskite loaded in a DAC under non-hydrostatic conditions. The influence of these factors can be clearly visualized by plotting the three-dimensional distribution of the deviatoric unit-cell volume strain in relation to the cylindrical axis of the DAC and indicates that, if the elasticity of a perovskite is nearly isotropic as it is for CaTiO3, the other two factors become relatively insignificant.

Structure Solution of the High-Pressure Phase of CuWO4 and Evolution of the Jahn–Teller Distortion

In this work, we have investigated the structural behavior of cuproscheelite up to 33.9 GPa by means of high-pressure single-crystal X-ray diffraction (SXRD) and extended X-ray absorption fine structure (EXAFS). According to EXAFS, beyond 9 GPa a phase transition takes place. On the basis of SXRD, the transition is from the triclinic (P1) structure to a monoclinic (P2/c) structure isotypic to wolframite. The transition implies abrupt changes of CuO6 and WO6 octahedra, but no coordination change. Further, we report the role played by the Jahn–Teller distortion of the CuO6 octahedra on the mechanism of the phase transition as well as the changes in the behavior of the Cu–O bonds for the triclinic and monoclinic phases of CuWO4. A second phase transition was detected at 22.5 GPa. Finally, a low-temperature experiment has been carried out at 100 K. No structural changes were detected for CuWO4, confirming the already known triclinic structure stability at room pressure and low temperature.

Silver the new gold standard for high-pressure single crystal X-ray diffraction

Silver the new gold standard for high-pressure single crystal X-ray diffraction

High-pressure displacive phase transition of a natural Mg-rich pigeonite

A high-pressure single-crystal X-ray diffraction study has been carried out on a P21/c natural Mg-rich pigeonite sample with composition ca. Wo6En76Fs18 using a diamond anvil-cell. The unit-cell parameters were determined at 14 different pressures to 7.14 GPa. The sudden disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 2.8%) in the unit-cell volume indicated a first-order P21/c–C2/c phase transition between 4.66 and 4.88 GPa. The P(V) data of the P21/c phase were fitted to 4.66 GPa by a third-order Birch–Murnaghan equation of state (BM3 EoS), whereas the limited number of experimental data collected within the C2/c phase between 4.88 and 7.14 GPa were fitted using the same equation of state but with K′ constrained to the value obtained for the P21/c fitting. The equation of state coefficients are V0 = 424.66(6) A3, KT0 = 104(2) GPa and K′ = 8(1) for the P21/c phase, and V0 = 423.6(1) A3, KT0 = 112.4(8) GPa, and K′ fixed to 8(1) for the C2/c phase. The axial moduli for a, b, and c for the P21/c phase were obtained using also a BM3-EoS, while for the C2/c phase only a linear calculation could be performed, and therefore the same approach was applied for comparison also to the P21/c phase. In general the C2/c phase exhibits axial compressibilities (βc > βa >> βb) lower than those of the P21/c phase (βb > βc ≈ βa; similar to those found in previous studies in clinopyroxenes and orthopyroxenes). The lower compressibility of the C2/c phase compared with that of the P21/c could be ascribed to the greater stiffness along the b direction. A previously published relationship between Pc and M2 average cation radius (i.r.) has been updated using all the literature data on P21/c clinopyroxene containing large cations at M2 site and our new data. The following weighted regression was obtained: Pc (GPa) = 26(4) − 28(5) × i.r (A), R2 = 0.97. This improved equation can be used to predict the critical pressure of natural P21/c clinopyroxene samples just knowing the composition at M2 site.

High-Pressure Study of Oxo-bridged Mixed-Valent MnIII/MnIV Dimers High-Pressure Study of Oxo-bridged Mixed-Valent MnIII/MnIV Dimers

A combination of high-pressure single crystal X-ray diffraction and high-pressure SQUID magnetometry has been used to study two oxo-bridged mixed-valent MnIII/MnIV dimers. [Mn2O2(bpy)4](ClO4)3·3CH3CN, (1·3CH3CN; bpy = 2,2ʹ-bipyridine) has been compressed to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3·2CH3CN·1H2O, (2·2CH3CN·1H2O) could be measured crystallographically up to 4.55 GPa. The PF6 salt of [Mn2O2(bpy)4]3+ has never been reported before while 1 has been reported as a hydrate and in a different crystallographic space group. The application of hydrostatic pressure imposes significant distortions and modifications in the structures of both complexes. In particular, in complex 1·3CH3CN the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond lengths, whilst in 2·2CH3CN·1H2O the Mn-O-Mn bridging angles and the Mn-O bond lengths are substantially unchanged. Interestingly 2·2CH3CN·1H2O also shows a constant contraction in nearly all the Mn-N bonds. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 1·3CH3CN and 0.84 GPa for 2·2CH3CN·1H2O.

High-pressure phase transition of a natural pigeonite

High-pressure and room-temperature single-crystal X-ray diffraction (XRD) studies have been performed on crystals of a natural pigeonite sample with composition ca. Wo10En43Fs47 using diamondanvil cells. The unit-cell parameters were determined at 18 different pressures up to about 6 GPa. A first-order P21/c-C2/c phase transition was found between 3.5 and 3.6 GPa, associated with the disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 1.7%) in the unit-cell volume. At the transition, a small hysteresis (~0.3 GPa) was observed. A third-order Birch-Murnaghan equation of state (BM3-EoS) fit to the 10 P-V data of the low-P phase yielded V0 = 431.93(2) Å3, KT0 = 96.8(8) GPa and K′ = 8.5(6). A second-order Birch-Murnaghan EoS fit to the 8 P-V data (between 3.6 and 6 GPa) of the C2/c high-P phase yielded V0 = 423.6(1) Å3 and KT0 = 112.4(8), indicating that the high-P C2/c phase is significantly stiffer than the low-P phase.

Pressure-Induced Cooperative Bond Rearrangement in a Zinc Imidazolate Framework: A High-Pressure Single-Crystal X-Ray Diffraction Study

The pressure-dependent structural evolution of a neutral zinc-imidazolate framework [Zn(2)(C(3)H(3)N(2))(4)](n) (ZnIm) has been investigated. The as-synthesized three-dimensional ZnIm network (alpha-phase) crystallizes in the tetragonal space group I4(1)cd (a = 23.5028(4) A, c = 12.4607(3) A). The ZnIm crystal undergoes a phase transition to a previously unknown beta-phase within the 0.543(5)-0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the beta-phase space group is I4(1) (a = 22.7482(3) A, c = 13.0168(3) A). The physical mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temperature bulk modulus for ZnIm is estimated to be approximately 14 GPa. This study represents the first example of a high-pressure single-crystal X-ray diffraction analysis of a metal-organic framework.