A comparison of the isostructural [Co(NH3)5NO2]XNO3 and [Co(NH3)5ONO]XNO3, X = Cl- or Br- in relation to nitro-nitrito linkage isomerization and photomechanical effects

A new photoactive cobalt coordination compound, [Co(NH3)5NO2]BrNO3 (I), was obtained. Its crystal structure was shown to be isostructural with previously known [Co(NH3)5NO2]ClNO3 (II) for which linkage isomerization accompanied with mechanical response of the crystal has been already reported. Single crystals of I are transformed into nitrito isomer [Co(NH3)5ONO]BrNO3 (III) on irradiation with blue light (λ = 465 nm) without being destroyed. The crystal structure of III was also solved using single-crystal X-ray diffraction and compared with previously known [Co(NH3)5ONO]ClNO3 (IV). A detailed comparison of the structures of I, II, III and IV, including unit-cell parameters, the distribution of free space (in particular, reaction cavities around the nitro ligand), the lengths of hydrogen bonds, coordination and Voronoi-Dirichlet polyhedra has been performed. Single-crystal X-ray diffraction data were complemented with IR spectra. The effect of the replacement of Cl- by Br- on the crystal structure and on the nitro-nitrito photoisomerization is discussed.

Elastic and piezoelectric properties of β-glycine - a quantum crystallography view on intermolecular interactions and a high-pressure phase transition

The effect of hydrostatic compression on the elastic and electronic properties of β-glycine was studied using a quantum crystallography approach. The interrelations between the changes in the microscopic quantum pressure in the electronic continuum, macroscopic compressibility and piezoelectricity were considered. The geometries and energies of hydrogen bonds in the crystal structure of β-glycine were considered as functions of pressure before and after a phase transition into the β'-phase in relation to the mechanism of this phase transition.

Structural changes in Rochelle salt on phase transitions revisited in a multi-temperature single-crystal X-ray diffraction study

Phase transitions in Rochelle salt [sodium potassium L(+)-tartrate tetrahydrate] are revisited in a single-crystal X-ray diffraction multi-temperature study on cooling from 308 to 100 K across the high-temperature paraelectric (PE) ↔ ferroelectric ↔ low-temperature PE phase transition points. The results of structure refinement using three different models (a harmonic with and without disorder, and an anharmonic) were compared. The temperature dependencies of anisotropic displacement parameters (ADPs) and Ueq, which can be calculated directly from ADPs, for the low-temperature PE phase indicate clearly the dynamic nature of disorder of the K1 atoms. The structures of the low-temperature and the high-temperature PE phases are compared for the first time at multiple temperatures for each phase based on diffraction data collected from the same single crystal. The data indicate that the high-temperature and the low-temperature paraelectric phases are probably not two different phases, as was assumed in earlier works, but are structurally the same phase at different temperatures.

Radiation damage as a source of information

The structural strain induced by temperature (`phonon pressure') and radiation damage (`defect pressure') is not necessarily correlated because of different underlying structural mechanisms. Here synchrotron experiments may provide new and yet unexplored opportunities. A recent publication by McMonagle et al. [(2024), Acta Cryst. B80, 13-18] is an excellent illustration of this.

A high-pressure single-crystal X-ray diffraction study of potassium guaninate hydrate, K+·C5H4N5O-·H2O

The crystal structure of potassium guaninate hydrate, K+·C5H4N5O-·H2O, was studied in the pressure range of 1 atm to 7.3 GPa by single-crystal diffraction using synchrotron radiation and a laboratory X-ray diffraction source. Structural strain was compared to that of the same salt hydrate on cooling, and in 2Na+·C5H3N5O2-·7H2O under hydrostatic compression and on cooling. A polymorphic transition into a new, incommensurately modulated, phase was observed at ∼4-5 GPa. The transition was reversible with a hysteresis: the satellite reflections disappeared on decompression to ∼1.4 GPa.

From geology to biology: an interdisciplinary course in crystal growth

The authors share experience of teaching an interdisciplinary university course in crystal growth with examples ranging from geology to biology.

This contribution shares experience of teaching an interdisciplinary university course in crystal growth with examples ranging from geology to biology. This is an attempt to combine teaching the basics of the classical and non-classical theories of crystallization with impressive examples of crystals growing around us and in the human body, as well as demonstration of the common phenomena in the growth of minerals in nature, crystalline materials in industry and the laboratory, and biomimetic and stimulus-responsive crystals. Lectures are supported by laboratory exercises. Students can also perform an individual research project and present an oral contribution at a mini-conference. Examples of the topics considered in the course are given, and an extensive list of references to papers and web resources is provided, which may be useful to those who want to implement anything from the authors’ experience.

Crystallography relevant to Mars and Galilean icy moons: crystal behavior of kieserite-type monohydrate sulfates at extraterrestrial conditions down to 15 K

Monohydrate sulfate kieserites (M ²⁺SO₄·H₂O) and their solid solutions are essential constituents on the surface of Mars and most likely also on Galilean icy moons in our solar system. Phase stabilities of end-member representatives (M ²⁺ = Mg, Fe, Co, Ni) have been examined crystallographically using single-crystal X-ray diffraction at 1 bar and temperatures down to 15 K, by means of applying open He cryojet techniques at in-house laboratory instrumentation. All four representative phases show a comparable, highly anisotropic thermal expansion behavior with a remarkable negative thermal expansion along the monoclinic b axis and a pronounced anisotropic expansion perpendicular to it. The lattice changes down to 15 K correspond to an 'inverse thermal pressure' of approximately 0.7 GPa, which is far below the critical pressures of transition under hydro-static compression (P_c ≥ 2.40 GPa). Consequently, no equivalent structural phase transition was observed for any compound, and neither dehydration nor rearrangements of the hydrogen bonding schemes have been observed. The M ²⁺SO₄·H₂O (M ²⁺ = Mg, Fe, Co, Ni) end-member phases preserve the kieserite-type C2/c symmetry; hydrogen bonds and other structural details were found to vary smoothly down to the lowest experimental temperature. These findings serve as an important basis for the assignment of sulfate-related signals in remote-sensing data obtained from orbiters at celestial bodies, as well as for thermodynamic considerations and modeling of properties of kieserite-type sulfate monohydrates relevant to extraterrestrial sulfate associations at very low temperatures.

N2–O2 icing in single-crystal in-house X-ray diffraction experiments using an open-flow helium cryostat

This note reports a study of the coating of a crystal with `ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The `ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers – periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.

Charge density studies of multicentre two-electron bonding of an anion radical at non-ambient temperature and pressure

The variation of charge density of two-electron multicentre bonding (pancake bonding) between semi-quinone radicals with pressure and temperature was studied on a salt of 5,6-di-chloro-2,3-di-cyano-semi-quinone radical anion (DDQ) with 4-cyano-N-methyl-pyridinium cation (4-CN) using the Transferable Aspheric Atom Model (TAAM) refinement. The pancake-bonded radical dimers are stacked by non-bonding π-interactions. With rising pressure, the covalent character of interactions between radicals increases, and above 2.55 GPa, the electron density indicates multicentric covalent interactions throughout the stack. The experimental charge densities were verified and corroborated by periodic DFT computations. The TAAM approach has been tested and validated for atomic resolution data measured at ambient pressure; this work shows this approach can also be applied to diffraction data obtained at pressures up to several gigapascals.

Phase transition in an organic ferroelectric: glycinium phosphite, with and without X-ray radiation damage

Thermal evolution of an organic ferroelectric, namely, glycinium phosphite, was probed by multi-temperature single-crystal diffraction using synchrotron radiation and also by a similar experiment with a laboratory X-ray diffractometer. Both series of measurements showed a transition from the paraelectric to the ferroelectric state at nearly the same temperature, T_c = 225 K. Temperature evolution of the unit-cell parameters and volume are drastically different for the synchrotron and laboratory data. The latter case corresponds to previous reports and shows an expected contraction of the cell on cooling. The data collected with the synchrotron beam show an abnormal nonlinear increase in volume on cooling. Structure analysis shows that this volume increase is accompanied by a suppression of scattering at high angles and an apparent increase of the anisotropic displacement parameters for all atoms; we therefore link these effects to radiation damage accumulated during consecutive data collections. The effects of radiation on the formation of the polar structure of ferroelectric glycinium phosphite is discussed together with the advantages and drawbacks of synchrotron experimentation with fine temperature sampling.

Tribochemistry, Mechanical Alloying, Mechanochemistry: What is in a Name?

Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we hope will spark timely and constructive discussion across the international mechanochemical community.

State-of-the-Art of Eggshell Waste in Materials Science: Recent Advances in Catalysis, Pharmaceutical Applications, and Mechanochemistry

Eggshell waste is among the most abundant waste materials coming from food processing technologies. Despite the unique properties that both its components (eggshell, ES, and eggshell membrane, ESM) possess, it is very often discarded without further use. This review article aims to summarize the recent reports utilizing eggshell waste for very diverse purposes, stressing the need to use a mechanochemical approach to broaden its applications. The most studied field with regards to the potential use of eggshell waste is catalysis. Upon proper treatment, it can be used for turning waste oils into biodiesel and moreover, the catalytic effect of eggshell-based material in organic synthesis is also very beneficial. In inorganic chemistry, the eggshell membrane is very often used as a templating agent for nanoparticles production. Such composites are suitable for application in photocatalysis. These bionanocomposites are also capable of heavy metal ions reduction and can be also used for the ozonation process. The eggshell and its membrane are applicable in electrochemistry as well. Due to the high protein content and the presence of functional groups on the surface, ESM can be easily converted to a high-performance electrode material. Finally, both ES and ESM are suitable for medical applications, as the former can be used as an inexpensive Ca2+ source for the development of medications, particles for drug delivery, organic matrix/mineral nanocomposites as potential tissue scaffolds, food supplements and the latter for the treatment of joint diseases, in reparative medicine and vascular graft producing. For the majority of the above-mentioned applications, the pretreatment of the eggshell waste is necessary. Among other options, the mechanochemical pretreatment has found an inevitable place. Since the publication of the last review paper devoted to the mechanochemical treatment of eggshell waste, a few new works have appeared, which are reviewed here to underline the sustainable character of the proposed methodology. The mechanochemical treatment of eggshell is capable of producing the nanoscale material which can be further used for bioceramics synthesis, dehalogenation processes, wastewater treatment, preparation of hydrophobic filters, lithium-ion batteries, dental materials, and in the building industry as cement.

Co-crystals of polyhalogenated diaminobenzonitriles with 18-crown-6: effect of fluorine on the stoichiometry and supramolecular structure

Fluorine in the ortho-position of diaminobenzonitrile promotes the formation of the N–H⋯NC bond which results in a 3D supramolecular structure of the co-crystal.

A cocrystal of L-ascorbic acid with picolinic acid: the role of O-H...O, N-H...O and C-H...O hydrogen bonds and L-ascorbic acid conformation in structure stabilization

A new 1:1 cocrystal (L-Asc-Pic) of L-ascorbic acid (vitamin C) with picolinic acid was prepared as a powder and as single crystals. The crystal structure was solved and refined from single-crystal X-ray diffraction (SCXRD) data collected at 293 (2) and 100 (2) K. The samples of the L-Asc-Pic cocrystal were characterized by elemental (HCNS) analysis and titrimetric methods, TG/DTG/DSC, and IR and Raman spectroscopy. The asymmetric unit comprises a picolinic acid zwitterion and an L-ascorbic acid molecule. The stabilization energy of intermolecular interactions involving hydrogen bonds, the vibrational spectrum and the energies of the frontier molecular orbitals were calculated using the GAUSSIAN09 and the CrystalExplorer17 programs. The charge distribution on the atoms of the L-Asc-Pic cocrystal, L-ascorbic acid itself and its 12 known cocrystals (structures from Version 5.40 of the Cambridge Structural Database) were calculated by the methods of Mulliken, Voronoi and Hirshfeld charge analyses (ADF) at the bp86/TZ2P+ level of theory. The total effective charges and conformations of the L-ascorbic acid molecules in the new and previously reported cocrystals were compared with those of the two symmetry-independent molecules in the crystals of L-ascorbic acid. A correlation between molecular conformation and its effective charge is discussed.

Pancake-bonding of semiquinone radicals under variable temperature and pressure conditions

The effects of temperature (100-370 K) and pressure (0-6 GPa) on the non-localized two-electron multicentric covalent bonds (`pancake bonding') in closely bound radical dimers were studied using single-crystal X-ray diffraction on a 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone radical anion (DDQ) as the sample compound. On cooling, the anisotropic structural compression was accompanied by continuous changes in molecular stacking; the discontinuities in the changes in volume and b and c cell parameters suggest that a phase transition occurs between 210 and 240 K. At a pressure of 2.55 GPa, distances between radical dimers shortened to 2.9 Å, which corresponds to distances observed in extended π-bonded polymers. Increasing pressure further to 6 GPa reduced the interplanar separation of the radicals to 2.75 Å. This may indicate that the covalent component of the interaction significantly increased, in accordance with the results of DFT calculations reported elsewhere [Molčanov et al. (2019), Cryst. Growth Des. 19, 391-402].

A novel crystal form of metacetamol: the first example of a hydrated form

We report the crystal structure and crystallization conditions of a first hydrated form of metacetamol (a hemihydrate), C₈H₉NO₂·0.5H₂O. It crystallizes from metacetamol-saturated 1:1 (v/v) water-ethanol solutions in a monoclinic structure (space group P2₁/n) and contains eight metacetamol and four water molecules per unit cell. The conformations of the molecules are the same as in polymorph II of metacetamol, which ensures the formation of hydrogen-bonded dimers and R₂²(16) ring motifs in its crystal structure similar to those in polymorph II. Unlike in form II, however, these dimers in the hemihydrate are connected through water molecules into infinite hydrogen-bonded molecular chains. Different chains are linked to each other by metacetamol-water and metacetamol-metacetamol hydrogen bonds, the latter type being also present in polymorph I. The overall noncovalent network of the hemihydrate is well developed and several types of hydrogen bonds are responsible for its formation.

Completing the picture of tolazamide polymorphism under extreme conditions: a low-temperature study

We present the results of an experimental and computational study of structural changes in two polymorphs of tolazamide {systematic name: 1-[(azepan-1-ylamino)carbonyl]-4-methylbenzenesulfonamide}, C₁₄H₂₁N₃O₃S, on cooling to 100 K and reverse heating. No phase transitions occurred in this temperature range. The anisotropy of the thermal expansion was different for the two polymorphs and differed from that reported previously for the hydrostatic compression. The changes in different intermolecular contacts responsible for the strain anisotropy were analysed. Relative shortening of the contacts was related directly to their initial length and reversely to the steric density around them. Increasing steric density is likely to be the driving force for the conformational ordering of the azepane ring under compression.

A large anisotropic plasticity of L-leucinium hydrogen maleate preserved at cryogenic temperatures

L-Leucinium hydrogen maleate crystals are very plastic at ambient conditions. Here it is shown that this plasticity is preserved at least down to 77 K. The structural changes in the temperature range 293-100 K were followed in order to rationalize the large anisotropic plasticity in this compound. To the best of our knowledge, this is the first reported example of an organic compound remaining so plastic at cryogenic conditions.

Ball size or ball mass – what matters in organic mechanochemical synthesis?

The effects of milling ball mass, size and material are isolated for a model mechanochemical co-crystallisation.

Effect of pressure on slit channels in guanine sodium salt hydrate: a link to nucleobase intermolecular interactions

The crystal structure of a hydrate of the sodium salt of guanine (2Na⁺·C₅H₃N₅O²⁻·7H₂O) was studied at high pressure by single-crystal X-ray diffraction and Raman spectroscopy.

An acetonitrile-solvated cocrystal of piroxicam and succinic acid with co-existing zwitterionic and non-ionized piroxicam molecules

This work reports a new acetonitrile (ACN)-solvated cocrystal of piroxicam (PRX) and succinic acid (SA), 2C₁₅H₁₃N₃O₄S·0.5C₄H₆O₄·C₂H₃N or PRX:SA:ACN (4:1:2), which adopts the triclinic space group P-1. The outcome of crystallization from ACN solution can be controlled by varying only the PRX:SA ratio, with a higher PRX:SA ratio in solution unexpectedly favouring a lower stoichiometric ratio in the solid product. In the new solvate, zwitterionic (Z) and non-ionized (NI) PRX molecules co-exist in the asymmetric unit. In contrast, the nonsolvated PRX-SA cocrystal contains only NI-type PRX molecules. The ACN molecule entrapped in PRX-SA·ACN does not form any hydrogen bonds with the surrounding molecules. In the solvated cocrystal, Z-type molecules form dimers linked by intermolecular N-H...O hydrogen bonds, whereas every pair of NI-type molecules is linked to SA via N-H...O and O-H...N hydrogen bonds. Thermogravimetry and differential scanning calorimetry suggest that thermal desolvation of the solvate sample occurs at 148 °C, and is followed by recrystallization, presumably of a multicomponent PRX-SA structure. Vibrational spectra (IR and Raman spectroscopy) of PRX-SA·ACN and PRX-SA are also used to demonstrate the ability of spectroscopic techniques to distinguish between NI- and Z-type PRX molecules in the solid state. Hence, vibrational spectroscopy can be used to distinguish the PRX-SA cocrystal and its ACN solvate.

High pressure: a complementary tool for probing solid-state processes

High pressure offers insight into the mechanisms of a wide range of solid-state phenomena occurring under atmospheric pressure conditions.

Studying weak inter-actions in crystals at high pressures: when hardware matters

The quality of structural models for 1,2,4,5-tetra-bromo-benzene (TBB), C6H2Br4, based on data collected from a single crystal in a diamond anvil cell at 0.4 GPa in situ using two different diffractometers belonging to different generations have been compared, together with the effects of applying different data-processing strategies.

The effect of ball mass on the mechanochemical transformation of a single-component organic system: anhydrous caffeine

Mechanochemical methodologies, particularly ball milling, have become commonplace in many laboratories. In the present work, we examine the effects of milling ball mass on the polymorphic conversion of anhydrous caffeine. By investigating a single-phase system, the rate-limiting step of particle-particle contact formation is eliminated. It is found that larger milling balls lead to considerably faster conversion rates. Modelling of the transformation rate suggests that a single, time-independent rate constant is insufficient to describe the transformation. Instead, a convolution of at least two rate-determining processes is required to correctly describe the transformation. This suggests that the early stages of the transformation are governed only by the number of particle-ball collisions. As the reaction proceeds, these collisions less frequently involve reactant, and the rate becomes limited by mass transport, or mixing, even in originally single-phase systems, which become multi-phase as the product is formed. Larger milling balls are less hindered by poorly mixed material. This likely results from a combination of higher impact energies and higher surface areas associated with the larger milling balls. Such insight is important for the selective and targeted design of mechanochemical processes.

Anisotropic lattice softening near the structural phase transition in the thermosalient crystal 1,2,4,5-tetrabromobenzene

The thermosalient effect (crystal jumping on heating) attracts much attention as both an intriguing academic phenomenon and in relation to its potential for the development of molecular actuators but its mechanism remains unclear. 1,2,4,5-Tetrabromobenzene (TBB) is one of the most extensively studied thermosalient compounds that has been shown previously to undergo a phase transition on heating, accompanied by crystal jumping and cracking. The difference in the crystal structures and intermolecular interaction energies of the low- and high-temperature phases is, however, too small to account for the large stress that arises over the course of the transformation. The energy is released spontaneously, and crystals jump across distances that exceed the crystal size by orders of magnitude. In the present work, the anisotropy of lattice strain is followed across the phase transition by single-crystal X-ray diffraction, focusing on the structural evolution from 273 to 343 K. A pronounced lattice softening is observed close to the transition point, with the structure becoming more rigid immediately after the phase transition. The diffraction studies are further supported by theoretical analysis of pairwise intermolecular energies and zone-centre lattice vibrations. Only three modes are found to monotonically soften up to the phase transition, with complex behaviour exhibited by the remaining lattice modes. The thermosalient effect is delayed with respect to the structural transformation itself. This can originate from the martensitic mechanism of the transformation, and the accumulation of stress associated with vibrational switching across the phase transition. The finding of this study sheds more light on the nature of the thermosalient effect in 1,2,4,5-tetrabromobenzene and can be applicable also to other thermosalient compounds.

Ball-free mechanochemistry: in situ real-time monitoring of pharmaceutical co-crystal formation by resonant acoustic mixing

Co-crystal formation by resonant acoustic mixing was followed for the first time by in situ real-time X-ray powder diffraction.

Polymorphism of chlorpropamide on liquid-assisted mechanical treatment: choice of liquid and type of mechanical treatment matter

Different types of mechanical treatment (tableting, grinding, milling, etc.) are important technological operations in the pharmaceutical industry.

Structural aspects of displacive transformations: what can optical microscopy contribute? Dehydration of Sm2(C2O4)3·10H2O as a case study

For martensitic transformations the macroscopic crystal strain is directly related to the corresponding structural rearrangement at the microscopic level. In situ optical microscopy observations of the interface migration and the change in crystal shape during a displacive single crystal to single crystal transformation can contribute significantly to understanding the mechanism of the process at the atomic scale. This is illustrated for the dehydration of samarium oxalate decahydrate in a study combining optical microscopy and single-crystal X-ray diffraction.

Challenges of Mechanochemistry: Is In Situ Real-Time Quantitative Phase Analysis Always Reliable? A Case Study of Organic Salt Formation

Mechanochemical methods offer unprecedented academic and industrial opportunities for solvent-free synthesis of novel materials. The need to study mechanochemical mechanisms is growing, and has led to the development of real-time in situ X-ray powder diffraction techniques (RI-XRPD). However, despite the power of RI-XRPD methods, there remain immense challenges. In the present contribution, many of these challenges are highlighted, and their effect on the interpretation of RI-XRPD data considered. A novel data processing technique is introduced for RI-XRPD, through which the solvent-free mechanochemical synthesis of an organic salt is followed as a case study. These are compared to ex situ studies, where notable differences are observed. The process is monitored over a range of milling frequencies, and a nonlinear correlation between milling parameters and reaction rate is observed. Kinetic analysis of RI-XRPD allows, for the first time, observation of a mechanistic shift over the course of mechanical treatment, resulting from time evolving conditions within the mechanoreactor.

Crystal structure of 4-benzyl-carbamoyl-1-methyl-pyridin-1-ium iodide: an efficient multimodal anti-viral drug

In the title compound, [MeC₅H₄NCONHCH₂C₆H₅]I or C₁₄H₁₅N₂O⁺·I^-, a cation and an anion form an ionic pair linked by a strong N-H⋯I hydrogen bond. In the crystal, ionic pairs linked by weak C-H⋯I hydrogen bonds form infinite ribbons along the crystallographic a axis. Polymorphism screening varying crystallization solvents (water, acetone 90%-water, ethanol 90%-water, 2-propanol 90%-water, DMF, DMSO, methanol, aceto-nitrile) and conditions (solution temperature, heating and cooling protocols) did not reveal any other polymorphs than the one reported in this work.

Isostructural crystal hydrates of rare-earth metal oxalates at high pressure: from strain anisotropy to dehydration

The crystal structures of a series of isostructural rare-earth metal oxalates, (REE)2(C2O4)3·10H2O (REE=Sm, Y) and a 1:1 YSm(C2O4)3·10H2O solid solution, have been studied in situ by single-crystal X-ray diffraction and optical microscopy. The structures were followed from ambient pressure to 6 GPa in a DAC with paraffin as the hydrostatic fluid. Bulk compressibilities, anisotropic lattice strain on hydrostatic compression and the corresponding changes in the atomic coordinates were followed. Discontinuities/sharp changes in the slopes of the pressure dependences of volume and selected cell parameters have been observed for yttrium-containing salts at ~3.5 GPa. This may be related to the re-distribution of water molecules within the crystal structure. Y2(C2O4)3·10H2O undergoes a partial dehydration at 1 GPa, forming monoclinic Y2(C2O4)3·6H2O as single-crystalline inclusions in the original phase.

Large porous particles for respiratory drug delivery. Glycine-based formulations

Large porous particles are becoming increasingly popular as carriers for pulmonary drug delivery with both local and systemic applications. These particles have high geometric diameters (5-30μm) but low bulk density (~0.1g/cm³ or less) such that the aerodynamic diameter remains low (1-5μm). In this study salbutamol and budesonide serve as model inhalable drugs with poor water solubility. A novel method is proposed for the production of dry powder inhaler formulations with enhanced aerosol performance (e.g. for salbutamol-glycine formulation the fine particle fraction (FPF≤4.7μm) value is 67.0±1.3%) from substances that are poorly soluble in water. To overcome the problems related to extremely poor aqueous solubility of the APIs, not individual solvents are used for spray freeze-drying of API solutions, but organic-water mixtures, which can form clathrate hydrates at low temperatures and release APIs or their complexes as fine powders, which form large porous particles after the clathrates are removed by sublimation. Zwitterionic glycine has been used as an additive to API directly in solutions prior to spray freeze-drying, in order to prevent aggregation of powders, to enhance their dispersibility and improve air-flow properties. The clathrate-forming spray freeze-drying process in the multi-component system was optimized using low-temperature powder X-ray diffraction and thermal analysis.

Breakthrough in the high-pressure structures of Ba based on full exploitation of aperiodic symmetry

A breakthrough in the high-pressure structures of Ba based on a full exploitation of aperiodic symmetry is discussed in the general context of the 'complex structures of simple metals'.

New 1:1 and 2:1 salts in the `DL-norvaline–maleic acid' system as an example of assembling various crystal structures from similar supramolecular building blocks

Molecular salts and cocrystals of amino acids have potential applications as molecular materials with nonlinear optical, ferroelectric, piezoelectric, and other various target physical properties. The wide choice of amino acids and coformers makes it possible to design various crystal structures. The amino acid–maleic acid system provides a perfect example of a rich variety of crystal structures with different stoichiometries, symmetries and packing motifs built from the molecular building blocks, which are either exactly the same, or differ merely by protonation or as optical isomers. The present paper reports the crystal structures of two new salts of the DL-norvaline–maleic acid system with 1:1 and 2:1 stoichiometries, namely DL-norvalinium hydrogen maleate, C5H12NO2 +·C4H3O4 −, (I), and DL-norvalinium hydrogen maleate–DL-norvaline, C5H12NO2 +·C4H3O4 −·C5H11NO2, (II). These are the first examples of molecular salts of DL-norvaline with an organic anion. The crystal structure of (I) has the same C 2 2(12) structure-forming motif which is common for hydrogen maleates of amino acids. The structure of (II) has dimeric cations. Of special interest is that the single crystals of (I) which are originally formed on crystallization from aqueous solution transform into single crystals of (II) if stored in the mother liquor for several hours.

Pressure-driven phase transition mechanisms revealed by quantum chemistry: l-serine polymorphs

The present study delivers a computational approach for the understanding of the mechanism of phase transitions between polymorphs of small organic molecules.

A new solvate of furosemide with dimethylacetamide

The loop diuretic furosemide is used widely in the treatment of congestive heart failure and edema, and is practically insoluble in water. The physicochemical and pharmacokinetic properties of drugs can be modified by preparing the drug in an appropriate solid-state form. A new solvate of furosemide with dimethylacetamide (DMA) {systematic name: 4-chloro-2-[(furan-2-yl)methylamino]-5-sulfamoylbenzoic acid N,N-dimethylacetamide disolvate}, C₁₂H₁₁ClN₂O₅S·2C₄H₉NO, (I), is reported. The channeled structure formed on slow crystallization contains DMA solvent molecules in its channels. This structure adds to the evidence of varied conformations observed across all known structures, so supporting the idea that this flexible molecule has conformational lability. The current structure also differs from those of other previously known furosemide solvates in the number of solvent molecules per furosemide molecule, viz. 2:1 instead of 1:1. Desolvation of (I) gives the most stable form of furosemide, i.e. Form I.

Crystal structure of a 2:1 co-crystal of meloxicam with acetyl-endi-carb-oxy-lic acid

The pharmaceutical 2:1 co-crystal of meloxicam [MXM; systematic name: 4-hy-droxy-2-methyl-N-(5-methyl-thia-zol-2-yl)-2H-1,2-benzo-thia-zine-3-carboxamide 1,1-dioxide] with acetyl-enedi-carb-oxy-lic acid (ACA; systematic name: but-2-ynedioic acid), crystallizes with one MXM mol-ecule and half an ACA mol-ecule in the asymmetric unit, C₁₄H₁₃N₃O₄S₂·0.5C₄H₂O₄. The mid-point of the triple bond of ACA is located on an inversion centre. In the crystal, the two stereoisomers of MXM with respect to the N atom of the sulfonamide group are related by the inversion centre. The carbonyl and hy-droxy groups belonging to the MXM mol-ecule are involved in an intra-molecular O-H⋯O hydrogen bond. The structure-forming motif includes two MXM mol-ecules linked via an ACA conformer through N-H⋯O and O-H⋯N hydrogen bonds, similar to MXM co-crystals with other di-carb-oxy-lic acids.