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.

Hysteretic Room-Temperature Magnetic Bistability of the Crystalline 4,7-Difluoro-1,3,2-Benzodithiazolyl Radical.

The title radical R⋅, synthesized by reduction of the corresponding cation R+, is thermally stable up to ~380 K in the crystalline state under anaerobic conditions. With SQUID magnetometry, single-crystal and powder XRD, solid-state EPR and TG-DSC, reversible spin-Peierls transition between diamagnetic and paramagnetic states featuring ~10 K hysteretic loop is observed for R⋅ in the temperature range ~310-325 K; ΔH=~2.03 kJ mol-1 and ΔS=~6.23 J mol-1 K-1. The transition is accompanied by mechanical movement of the crystals, i. e., by thermosalient behavior. The low-temperature diamagnetic P-1 polymorph of R⋅ consists of R⋅2 π-dimers arranged in (…R⋅2…)n π-stacks; whereas the high-temperature paramagnetic P21/c polymorph, of uniform (…R⋅…)n π-stacks. With the XRD geometries, CASSCF and broken-symmetry DFT jointly suggest strong antiferromagnetic (AF) interactions within R⋅2 and weak between R⋅2 for the (…R⋅2…)n stacks; and moderate AF interactions between R⋅ for the (…R⋅…)n stacks. The fully hydrocarbon archetype of R⋅ does not reveal the aforementioned properties. Thus, the fluorinated 1,3,2-benzodithiazolyls pave a new pathway in the design and synthesis of metal-less magnetically-bistable materials.

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.

Two new bismuth salts with succinic acid: synthesis, structural, spectroscopic and thermal characterization.

Two novel bismuth succinate hydrates, namely, poly[[diaqua(µ3-butane-1,4-dicarboxylato)hemi(µ-butane-1,4-dicarboxylato)bismuth] monohydrate], {[Bi(C4H4O4)1.5(H2O)2]·H2O}n (1), and poly[[µ-aqua-aqua(µ3-butane-1,4-dicarboxylato)(µ-butane-1,4-dicarboxylato)-µ-oxido-dibismuth] monohydrate], {[Bi2(C4H4O4)2O(H2O)2]·H2O}n (2), have been synthesized. Their crystal structures were determined by single-crystal X-ray diffraction and the compounds were characterized by IR and Raman spectroscopy, powder X-ray diffraction and thermal analysis. The crystal structure analysis revealed that the compounds are coordination polymers, with 1 having a two-dimensional layered structure and 2 displaying a three-dimensional (3D) framework. Fully deprotonated succinate anions (C4H4O42-) in two different conformations (trans and gauche) are included in their composition. The Bi3+ cations are surrounded by O atoms from the carboxylate groups of succinate anions and aqua ligands. BiO9 coordination polyhedra in 1 are connected in pairs by edges. These pairs are bound together by bridging succinate ligands to form layers. Bismuth coordination polyhedra of two different types (BiO9 and BiO7) in 2 are connected by edges to form infinite ribbons. Ribbons of polyhedra with bridging succinate ligands form a 3D polymeric structure.

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.

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.

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].

Protein/Ice Interaction: High-Resolution Synchrotron X-ray Diffraction Differentiates Pharmaceutical Proteins from Lysozyme.

Protein/ice interactions are investigated by a novel method based on measuring the characteristic features of X-ray diffraction (XRD) patterns of hexagonal ice (Ih). Aqueous solutions of four proteins and other solutes are studied using high-resolution synchrotron XRD. Two pharmaceutical proteins, recombinant human albumin and monoclonal antibody (both at 100 mg/mL), have a pronounced effect on the properties of ice crystals, reducing the size of the Ih crystalline domains and increasing the microstrain. Lysozyme (100 mg/mL) and an antifreeze protein (1 mg/mL) have much weaker impact on Ih. Neither of the proteins studied exhibit preferred interactions with specific crystalline faces of Ih. It is proposed that the pharmaceutical proteins interact with ice crystals indirectly by accumulating in the quasi-liquid layer next to ice crystallization front, rather than directly, via a sorption on ice crystals. This is the first report, to the best of our knowledge, of major difference in the protein/ice interaction between non-antifreeze proteins. Another important finding is a detection of a second (minor) population of ice crystals, which is tentatively identified as a high-pressure form of ice, possibly IceIII or IceIX. This finding highlights a potential role of mechanical stresses in freeze-induced destabilization of proteins.

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.

Quantification of photoinduced bending of dynamic molecular crystals: from macroscopic strain to kinetic constants and activation energies.

Photomechanically reconfigurable elastic single crystals are the key elements for contactless, timely controllable and spatially resolved transduction of light into work from the nanoscale to the macroscale. The deformation in such single-crystal actuators is observed and usually attributed to anisotropy in their structure induced by the external stimulus. Yet, the actual intrinsic and external factors that affect the mechanical response remain poorly understood, and the lack of rigorous models stands as the main impediment towards benchmarking of these materials against each other and with much better developed soft actuators based on polymers, liquid crystals and elastomers. Here, experimental approaches for precise measurement of macroscopic strain in a single crystal bent by means of a solid-state transformation induced by light are developed and used to extract the related temperature-dependent kinetic parameters. The experimental results are compared against an overarching mathematical model based on the combined consideration of light transport, chemical transformation and elastic deformation that does not require fitting of any empirical information. It is demonstrated that for a thermally reversible photoreactive bending crystal, the kinetic constants of the forward (photochemical) reaction and the reverse (thermal) reaction, as well as their temperature dependence, can be extracted with high accuracy. The improved kinematic model of crystal bending takes into account the feedback effect, which is often neglected but becomes increasingly important at the late stages of the photochemical reaction in a single crystal. The results provide the most rigorous and exact mathematical description of photoinduced bending of a single crystal to date.

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.

Crystal structure and proton conductivity of a new Cs3(H2PO4)(HPO4)·2H2O phase in the caesium di- and monohydrogen orthophosphate system.

The MxHy(AO4)z acid salts (M = Cs, Rb, K, Na, Li, NH4; A = S, Se, As, P) exhibit ferroelectric properties. The solid acids have low conductivity values and are of interest with regard to their thermal properties and proton conductivity. The crystal structure of caesium dihydrogen orthophosphate monohydrogen orthophosphate dihydrate, Cs3(H1.5PO4)2·2H2O, has been solved. The compound crystallizes in the space group Pbca and forms a structure with strong hydrogen bonds connecting phosphate tetrahedra that agrees well with the IR spectra. The dehydration of Cs3(H1.5PO4)2·2H2O with the loss of two water molecules occurs at 348-433 K. Anhydrous Cs3(H1.5PO4)2 is stable up to 548 K and is then converted completely into caesium pyrophosphate (Cs4P2O7) and CsPO3. Anhydrous Cs3(H1.5PO4)2 crystallizes in the monoclinic C2 space group, with the unit-cell parameters a = 11.1693 (4), b = 6.4682 (2), c = 7.7442 (3) Šand ß = 71.822 (2)°. The conductivities of both compounds have been measured. In contrast to crystal hydrate Cs3(H1.5PO4)2·2H2O, the dehydrated form has rather low conductivity values of ∼6 × 10-6-10-8 S cm-1 at 373-493 K, with an activation energy of 0.91 eV.

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.

Ice Recrystallization in a Solution of a Cryoprotector and Its Inhibition by a Protein: Synchrotron X-Ray Diffraction Study.

Ice formation and recrystallization is a key phenomenon in freezing and freeze-drying of pharmaceuticals and biopharmaceuticals. In this investigation, high-resolution synchrotron X-ray diffraction is used to quantify the extent of disorder of ice crystals in binary aqueous solutions of a cryoprotectant (sorbitol) and a protein, bovine serum albumin. Ice crystals in more dilute (10 wt%) solutions have lower level of microstrain and larger crystal domain size than these in more concentrated (40 wt%) solutions. Warming the sorbitol-water mixtures from 100 to 228 K resulted in partial ice melting, with simultaneous reduction in the microstrain and increase in crystallite size, that is, recrystallization. In contrast to sorbitol solutions, ice crystals in the BSA solutions preserved both the microstrain and smaller crystallite size on partial melting, demonstrating that BSA inhibits ice recrystallization. The results are consistent with BSA partitioning into quasi-liquid layer on ice crystals but not with a direct protein-ice interaction and protein sorption on ice surface. The study shows for the first time that a common (i.e., not-antifreeze) protein can have a major impact on ice recrystallization and also presents synchrotron X-ray diffraction as a unique tool for quantification of crystallinity and disorder in frozen aqueous systems.

Isoenergetic Polymorphism: The Puzzle of Tolazamide as a Case Study.

In the present case study of tolazamide we illustrate how many seemingly contradictory results that have been obtained from experimental observations and theoretical calculations can finally start forming a consistent picture: a "puzzle put together". For many years, tolazamide was considered to have no polymorphs. This made this drug substance unique among the large family of sulfonylureas, which was known to be significantly more prone to polymorphism than many other organic compounds. The present work employs a broad and in-depth analysis that includes the use of optical microscopy, single-crystal and powder X-ray diffraction, IR and Raman spectroscopies, DSC, semiempirical PIXEL calculations and DFT of three polymorphs of tolazamide. This case study shows how the polymorphs of a molecular crystal can be overlooked even if discovered serendipitously on one of numerous crystallizations, and how very different molecular packings can be practically isoenergetic but still crystallize quite selectively and transform one into another irreversibly upon heating.

L-Argininium phosphite - a new candidate for NLO materials.

In order to investigate the possibility of salt formation in the L-Arg-H3PO3-H2O system, single crystals of L-argininium phosphite, C6H15N4O2(+)·H2PO3(-), were prepared by evaporation of an aqueous solution containing equimolar quantities of L-arginine and phosphorous acid. The asymmetric unit contains one L-argininium(+) cation and one phosphite [HPO2(OH)](-) anion. The phosphite anions form chains parallel to [010] by O-H...O hydrogen bonding, with an O...O distance of 2.630 (3) Å. The protonated amine and guanidyl groups of the L-argininium(+) cations form N-H...O hydrogen bonds with the carboxylate groups and anions. The IR and Raman spectra are discussed in relation to the crystal structure. The salt displays nonlinear optical (NLO) properties. Another salt was obtained from a solution with a 1:2 molar ratio of components, but was characterized by vibrational spectra only.

Synthesis and structure-activity relationship of novel 1,4-diazabicyclo[2.2.2]octane derivatives as potent antimicrobial agents.

A series of new quaternary 1,4-diazabicyclo[2.2.2]octane derivatives was synthesized and evaluated for activity against several strains of both Gram positive and Gram negative bacteria and one strain of fungus under different inoculum size. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against six species of microorganisms were tested. Results show a clear structure-activity relationship between alkyl chain length of substitutions of 1,4-diazabicyclo[2.2.2]octane tertiary amine sites and antimicrobial activity. In the case of compounds 4a-4k, MIC was found to decrease with the increase of the alkyl chain length from ethyl to dodecyl and then to increase at higher chain length (n > 14). The MIC values were found to be low for the compounds 4f and 4g with alkyl chains ranging from 10 to 12 carbons in length (1.6 µg/ml) and were comparable to the reference drug Ciprofloxacin. Also, time-kill assay was performed to examine the bactericidal kinetics. Results indicated that 4f and 4g had rapid killing effects against Staphylococcus aureus, and eliminated 100% of the initial inoculum of bacteria in 2.5 h at the concentration of 10 µg/ml. In addition, compound 4g eliminate more than 99.9% of the initial inoculum of Ps. aeruginosa after 2.5 h of interaction but the activity of compound 4f against this species seems to be weak. Thus, 4g had strong bactericidal activity and could rapidly kill Gram positive S. aureus, as well as Gram negative Ps. aeruginosa at low and high inoculum size.

Dynamic single crystals: kinematic analysis of photoinduced crystal jumping (the photosalient effect).

Crystals on the move: If they are subjected to a strong light stimulus, crystals of the cobalt coordination compound [Co(NH3)5(NO2)]Cl(NO3) undergo sudden jumps and leap over distances 10(2)-10(5) times their own size to release the strain that accumulates in their interior. The first quantitative kinematic analysis of this phenomenon is reported. The observed effect could be employed for actuation on the macroscopic scale.