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.

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.

Elastic and piezoelectric properties of ß-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 ß-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 ß-glycine were considered as functions of pressure before and after a phase transition into the ß'-phase in relation to the mechanism of this phase transition.

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.

Spiers Memorial Lecture: Mechanochemistry, tribochemistry, mechanical alloying - retrospect, achievements and challenges.

The paper presents a view on the achievements, challenges and prospects of mechanochemistry. The extensive reference list can serve as a good entry point to a plethora of mechanochemical literature.

From geology to biology: an interdisciplinary course in crystal growth.

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.

Deletion Variants of Autotransporter from Psychrobacter cryohalolentis Increase Efficiency of 10FN3 Exposure on the Surface of Escherichia coli Cells.

The autotransporter AT877 from Psychrobacter cryohalolentis belongs to the family of outer membrane proteins containing N-terminal passenger and C-terminal translocator domains that form the basis for the design of display systems on the surface of bacterial cells. It was shown in our previous study that the passenger domain of AT877 can be replaced by the cold-active esterase EstPc or the tenth domain of fibronectin type III (10Fn3). In order to increase efficiency of the 10Fn3 surface display in Escherichia coli cells, four deletion variants of the Fn877 hybrid autotransporter were obtained. It was demonstrated that all variants are present in the membrane of bacterial cells and facilitate binding of the antibodies specific against 10Fn3 on the cell surface. The highest level of binding is provided by the variants Δ239 and Δ310, containing four and seven beta-strands out of twelve that comprise the structure of the translocator domain. Using electrophoresis under semi-native conditions, presence of heat modifiability in the full-size Fn877 and its deletion variants was demonstrated, which indicated preservation of beta structure in their molecules. The obtained results could be used to optimize the bacterial display systems of 10Fn3, as well as of other heterologous passenger domains.

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 (Pc ≥ 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.

Clathrate Hydrates of Organic Solvents as Auxiliary Intermediates in Pharmaceutical Research and Development: Improving Dissolution Behaviour of a New Anti-Tuberculosis Drug, Perchlozon.

There is an urgent need for new drugs to overcome the challenge of the ever-growing drug resistance towards tuberculosis. A new, highly efficient anti-tuberculosis drug, Perchlozone (thioureidoiminomethylpyridinium perchlorate, Pz), is only available in an oral dosage form, though injectable forms and inhalation solutions could be better alternatives, offering higher bioavailability. To produce such forms, nano- and micro-particles of APIs would need to be prepared as dispersions with carriers. We use this case study to illustrate the principles of selecting solvents and excipients when preparing such formulations. We justify the choice of water-THF (19.1 wt % THF) as solvent and mannitol as carrier to prepare formulations of Pz-a poorly soluble compound-that are suitable for injection or inhalation. The formulations could be prepared by conventional freeze-drying in vials, making the proposed method suitable for industrial scaling. A similar strategy for selecting the organic solvent and the excipient can be applied to other compounds with low water solubility.

Relating Excited States to the Dynamics of Macroscopic Strain in Photoresponsive Crystals.

Exposure of a photoreactive single crystal to light with a wavelength offset from its absorption maximum can have two distinct effects. The first is the "direct" effect, wherein the excited state generated in individual chemical species is influenced. The second is the "indirect" effect, which describes the penetration of light into the crystal and hence the spatial propagation and completeness of transformation. We illustrate using the nitro-nitrito isomerization of [Co(NH3)5NO2]Cl(NO3) as an example that the direct and indirect effects can be independently determined. This is achieved by comparing the dynamics of macroscopic crystal deformation (bending curvature and crystal elongation) induced by the photochemical reaction when irradiating a crystal at the absorption maximum and at different band edges (above or below the maximum) of the same band. Quantitative description of the macroscopic strain dynamics in comparison with experiments allowed us to suggest that irradiation at different tails of the same absorption band causes isomerization to proceed via different excited states and an additional photochemical reaction (presumably, reverse nitrito-nitro isomerization) can occur on irradiation at the ligand-field band edges.

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, Tc = 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.

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 [Molcanov et al. (2019), Cryst. Growth Des. 19, 391-402].