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A new polymorph of 1,3-diacetylpyrene has been obtained from its melt and thoroughly characterized using single-crystal X-ray diffraction, steady-state UV–Vis spectroscopy and periodic density functional theory calculations. Experimental studies covered the temperature range from 90 to 390 K and the pressure range from atmospheric to 4.08 GPa. Optimal sample placement in a diamond anvil cell according to our previously presented methodology ensured over 80% data coverage up to 0.8 Å for a monoclinic sample. Unrestrained Hirshfeld atom refinement of the high-pressure crystal structures was successful and anharmonic behavior of carbonyl oxygen atoms was observed. Unlike the previously characterized polymorph, the structure of 2°AP-β is based on infinite π-stacks of antiparallel 2°AP molecules. 2°AP-β displays piezochromism and piezofluorochromism which are directly related to the variation in interplanar distances within the π-stacking. The importance of weak intermolecular interactions is reflected in the substantial negative thermal expansion coefficient of −55.8 (57) MK−1 in the direction of C—H...O interactions.

Crystallography is a quintessential method for determining the atomic structure of crystals. The most common implementation of crystallography uses single crystals that must be of sufficient size, typically tens of micrometres or larger, depending on the complexity of the crystal structure. The emergence of serial data-collection methods in crystallography, particularly for time-resolved experiments, opens up opportunities to develop new routes to structure determination for nanocrystals and ensembles of crystals. Fluctuation X-ray scattering is a correlation-based approach for single-particle imaging from ensembles of identical particles, but has yet to be applied to crystal structure determination. Here, an iterative algorithm is presented that recovers crystal structure-factor intensities from fluctuation X-ray scattering correlations. The capabilities of this algorithm are demonstrated by recovering the structure of three small-molecule crystals and a protein crystal from simulated fluctuation X-ray scattering correlations. This method could facilitate the recovery of structure-factor intensities from crystals in serial crystallography experiments and relax sample requirements for crystallography experiments.

In the search for new active pharmaceutical ingredients, the precise control of the chemistry of cocrystals becomes essential. One crucial step within this chemistry is proton migration between cocrystal coformers to form a salt, usually anticipated by the empirical ΔpKa rule. Due to the effective role it plays in modifying intermolecular distances and interactions, pressure adds a new dimension to the ΔpKa rule. Still, this variable has been scarcely applied to induce proton-transfer reactions within these systems. In our study, high-pressure X-ray diffraction and Raman spectroscopy experiments, supported by DFT calculations, reveal modifications to the protonation states of the 4,4′-bipyridine (BIPY) and malonic acid (MA) cocrystal (BIPYMA) that allow the conversion of the cocrystal phase into ionic salt polymorphs. On compression, neutral BIPYMA and monoprotonated (BIPYH+MA−) species coexist up to 3.1 GPa, where a phase transition to a structure of P21/c symmetry occurs, induced by a double proton-transfer reaction forming BIPYH22+MA2−. The low-pressure C2/c phase is recovered at 2.4 GPa on decompression, leading to a 0.7 GPa hysteresis pressure range. This is one of a few studies on proton transfer in multicomponent crystals that shows how susceptible the interconversion between differently charged species is to even slight pressure changes, and how the proton transfer can be a triggering factor leading to changes in the crystal symmetry. These new data, coupled with information from previous reports on proton-transfer reactions between coformers, extend the applicability of the ΔpKa rule incorporating the pressure required to induce salt formation.

Since its founding in 2013, the Young Crystallographers (YC) have become one of the most active working groups not only within their parent organization, the German Crystallographic Society (DGK), but also among other young crystallographers' groups in Europe and the world. The aim of the YC is and always has been to support early-career researchers in the diverse fields of crystallography and the rejuvenation of the field on a national scale. Over the past decade, we have curated events, platforms, and educational content tailored to foster collaboration and knowledge transfer among young crystallographers. In this article, we introduce our group and show how this active and diverse community has shaped the rejuvenation of crystallography in Germany, strengthened by the support of our national society. [ABSTRACT FROM AUTHOR]

Many technologically important material properties are underpinned by disorder and short-range structural correlations; therefore, elucidating structure–property relationships in functional materials requires understanding both the average and the local structures. The latter information is contained within diffuse scattering but is challenging to exploit, particularly in single-crystal systems. Separation of the diffuse scattering into its constituent components can greatly simplify analysis and allows for quantitative parameters describing the disorder to be extracted directly. Here, a deep-learning method, DSFU-Net, is presented based on the Pix2Pix generative adversarial network, which takes a plane of diffuse scattering as input and factorizes it into the contributions from the molecular form factor and the chemical short-range order. DSFU-Net was trained on 198 421 samples of simulated diffuse scattering data and performed extremely well on the unseen simulated validation dataset in this work. On a real experimental example, DSFU-Net successfully reproduced the two components with a quality sufficient to distinguish between similar structural models based on the form factor and to refine short-range-order parameters, achieving values comparable to other established methods. This new approach could streamline the analysis of diffuse scattering as it requires minimal prior knowledge of the system, allows access to both components in seconds and is able to compensate for small regions with missing data. DSFU-Net is freely available for use and represents a first step towards an automated workflow for the analysis of single-crystal diffuse scattering.

From its conception, X-ray crystallography has provided a unique understanding of the structure, bonding and electronic state of materials, which, in turn, unlocks a means of examining the properties and function of crystalline systems. Using state-of-the-art single-crystal X-ray diffraction, along with UV–Vis spectroscopy and DFT calculations, Zwolenik et al. [(2024). IUCrJ, 11, 519–527] have provided a comprehensive study of the structure–optical property relationship of 1,3-diacetylpyrene with methodologies that are increasingly accessible to non-specialist laboratories.

An increasing variety of crystal structures has been observed in soft condensed matter over the past two decades, surpassing most expectations for the diversity of arrangements accessible through classical driving forces. Here, we survey the structural breadth of mesoscopic crystals—formed by micellar systems, nanoparticles, colloids, etc.—that have been observed in both soft matter experiments and coarse-grained self-assembly simulations. We review structure types that were found to mimic crystals on the atomic scale, as well as those that do not correspond to known geometries and seem to only occur on the mesoscale. While the number of crystal structure types observed in soft condensed matter still lags behind what is known from hard condensed matter, we hypothesize that the high tunability and diversity of building blocks that can be created on the nano- and microscale will render a structural variety that far exceeds that of atomic compounds, which are inevitably restricted by the "limitations" imposed by the periodic table of elements and by the properties of the chemical bond. An infusion of expertise in structural analysis from the field of crystallography into the soft condensed matter community will establish the common language necessary to report, compare, and organize the rapidly accruing structural knowledge gathered from simulations and experiments. The prospect of new materials created in soft matter and new, length-scale-spanning insights into the formation of ordered structures in both hard and soft condensed matter promise exciting new developments in the area of self-assembled mesoscale materials. [ABSTRACT FROM AUTHOR]

The microstructure and impact toughness in an ultra-high-strength casing were investigated, attempting to reveal the reason for toughness fluctuations along the casing in terms of crystallography. The morphological structures at the head of the casing are lath bainite, while those at the end are granular bainite and lath bainite. The head exhibits a higher density of high-angle grain boundaries dominated by block boundaries and a higher impact toughness than the end, showing an inhomogeneous microstructure and causing toughness fluctuations in the casing. The higher density of block boundaries in the head resulted from weaker variant selection because of its higher cooling rate than the end. Therefore, the underlying reason for the toughness fluctuations lies in the varying densities of the block boundaries along the casing triggered by uneven cooling. [ABSTRACT FROM AUTHOR]

The calculation of intermolecular interactions in molecular crystals using model energies provides a unified route to understanding the complex interplay of driving forces in crystallization, elastic properties and more. Presented here is a new single-parameter interaction energy model (CE-1p), extending the previous CrystalExplorer energy model and calibrated using density functional theory (DFT) calculations at the ωB97M-V/def2-QZVP level over 1157 intermolecular interactions from 147 crystal structures. The new model incorporates an improved treatment of dispersion interactions and polarizabilities using the exchange-hole dipole model (XDM), along with the use of effective core potentials (ECPs), facilitating application to molecules containing elements across the periodic table (from H to Rn). This new model is validated against high-level reference data with outstanding performance, comparable to state-of-the-art DFT methods for molecular crystal lattice energies over the X23 set (mean absolute deviation 3.6 kJ mol−1) and for intermolecular interactions in the S66x8 benchmark set (root mean-square deviation 3.3 kJ mol−1). The performance of this model is further examined compared to the GFN2-xTB tight-binding model, providing recommendations for the evaluation of intermolecular interactions in molecular crystal systems.

Single-crystal XRD crystallography discloses a new class of vdWs molecular crystals, long-chain tin(IV) alkanethiolates (Sn(SCnH2n+1)4, n ≥ 12). They exhibit a lamellar structure formed from molecular self-assembly due to the vdWs interactions of long all-trans alkyl chains, a nearly planar and rigid molecular geometry resulting from the coexistence of two trans and two gauche S–C bonds, and a variety of chain-length dependent physicochemical properties. [ABSTRACT FROM AUTHOR]

Hesperetin (HES) is a weakly acidic flavonoid of topical interest owing to its antiviral properties. Despite the presence of HES in many dietary supplements, its bioavailability is hindered by poor aqueous solubility (1.35 µg ml−1) and rapid first-pass metabolism. Cocrystallization has evolved as a promising approach to generate novel crystal forms of biologically active compounds and enhance the physicochemical properties without covalent modification. In this work, crystal engineering principles were employed to prepare and characterize various crystal forms of HES. Specifically, two salts and six new ionic cocrystals (ICCs) of HES involving sodium or potassium salts of HES were studied using single-crystal X-ray diffraction (SCXRD) or powder X-ray diffraction and thermal measurements. Structures of seven of the new crystalline forms were elucidated by SCXRD, which revealed two families of isostructural ICCs in terms of their crystal packing and confirmed the presence of phenol...phenolate (PhOH...PhO−) supramolecular heterosynthons. Diverse HES conformations were observed amongst these structures, including unfolded and folded (previously unreported) conformations. One ICC, HES with the sodium salt of HES (NESNAH), was scalable to the gram scale and found to be stable after accelerated stability testing (exposure to elevated heat and humidity). HESNAH reached Cmax after 10 min in PBS buffer 6.8 compared with 240 min in pure HES. In addition, relative solubility was observed to be 5.5 times greater, offering the possibility of improved HES bioavailability.

Lower-density polymorphs of dl-menthol were nucleated and crystallized in their high-pressure stability regions. Up to 0.30 GPa, the triclinic dl-menthol polymorph α, which is stable at atmospheric pressure, is less dense than a new β polymorph, which becomes stable above 0.40 GPa, but is less dense than the α polymorph at this pressure. The compression of polymorph α to at least 3.37 GPa is monotonic, with no signs of phase transitions. However, recrystallizations of dl-menthol above 0.40 GPa yield the β polymorph, which is less compressible and becomes less dense than α-dl-menthol. At 0.10 MPa, the melting point of the β polymorph is 14°C, much lower compared with those of α-dl-menthol (42–43°C) and l-menthol (36–38°C). The structures of both dl-menthol polymorphs α and β are very similar with respect to the lattice dimensions, the aggregation of OH...O molecules bonded into Ci symmetric chains, the presence of three symmetry-independent molecules (Z′ = 3), their sequence ABCC′B′A′, the disorder of the hydroxyl protons and the parallel arrangement of the chains. However, the different symmetries relating the chains constitute a high kinetic barrier for the solid–solid transition between polymorphs α and β, hence their crystallizations below or above 0.40 GPa, respectively, are required. In the structure of polymorph α, the directional OH...O bonds are shorter and the voids are larger compared with those in polymorph β, which leads to the reverse density relation of the polymorphs in their stability regions. This low-density preference reduces the Gibbs free-energy difference between the polymorphs: when polymorph α is compressed to above 0.40 GPa, the work component pΔV counteracts the transition to the less dense polymorph β, and on reducing the pressure of polymorph β to below 0.40 GPa, its transition to the less dense polymorph α is also hampered by the work contribution.

A new compound, C23H20BrN3OS, containing a quinoline-based iminothiazoline with a thiazoline ring, was synthesized and its crystal and molecular structures were analyzed through single crystal X-ray analysis. The compound belongs to the triclinic system P − 1 space group, with dimensions of a = 9.2304 (6) Å, b = 11.1780 (8) Å, c = 11.3006 (6) Å, α = 107.146 (5)°, β = 93.701 (5)°, γ = 110.435 (6)°, Z = 2 and V = 1025.61 (12) Å3. The crystal structure showed that C–H···N and C–H···O hydrogen bond linkages, forming infinite double chains along the b-axis direction, and enclosing R22(14) and R22(16) ring motifs. The Hirshfeld surface analysis revealed that H...H (44.1%) and H...C/C...H (15.3%) interactions made the most significant contribution. The newly synthesized (Z)-4-bromo-N-(4-butyl-3 (quinolin-3-yl)thiazol-2(3H)-ylidene)benzamide, in comparison to oleanolic acid, exhibited more strong potential against elastase with an inhibition value of 1.21 µM. Additionally, the derivative was evaluated using molecular docking and molecular dynamics simulation studies, which showed that the quinoline based iminothiazoline derivative has the potential to be a novel inhibitor of elastase enzyme. Both theoretical and experimental findings suggested that this compound could have a number of biological activities. [ABSTRACT FROM AUTHOR]

DNA has been used as a robust material for the building of a variety of nanoscale structures and devices owing to its unique properties. Structural DNA nanotechnology has reported a wide range of applications including computing, photonics, synthetic biology, biosensing, bioimaging, and therapeutic delivery, among others. Nevertheless, the foundational goal of structural DNA nanotechnology is exploiting DNA molecules to build three‐dimensional crystals as periodic molecular scaffolds to precisely align, obtain, or collect desired guest molecules. Over the past 30 years, a series of 3D DNA crystals have been rationally designed and developed. This review aims to showcase various 3D DNA crystals, their design, optimization, applications, and the crystallization conditions utilized. Additionally, the history of nucleic acid crystallography and potential future directions for 3D DNA crystals in the era of nanotechnology are discussed. [ABSTRACT FROM AUTHOR]

We have selected a set of ten 'golden oldies', diverse crystallography articles to illustrate important moments in the development of our field of science and which form landmark papers in crystallography. They are a mixture of 'science pull and technology push'. For each of our choices, we firstly created a new title that emphasizes how the paper's importance worked out from today's perspective. Then we describe the core details and impacts of each paper, with some quotations and a selected figure or two. Ten is an arbitrary number of highlights and our choice is personal. [ABSTRACT FROM AUTHOR]

NpO2(NO3)2 units are connected by bis(2-pyrrolidone) linker molecules with the trans-1,4-cyclohexyl bridging part (L1) to form a one-dimensional coordination polymer, [NpO2(NO3)2(L1)]n. Molecular and crystal structures of this compound are nearly identical to that of the UO22+ analogue, while its aqueous solubility is greatly enhanced, probably owing to weaker thermodynamic stability of the complexation in NpO22+ compared with that in UO22+. [ABSTRACT FROM AUTHOR]

Identifying whether two experimental crystal structures determined under different experimental conditions correspond to the same polymorph is a challenging problem in crystallography, and its solution has practical (and even legal) implications for various technological fields as well as for molecular crystal structure prediction. In this work, we assess the popular COMPACK method vis a vis powder X-ray diffraction (PXRD)-based comparison methods using a dataset of 44 939 structure pairs employed in a previous study [CrystEngComm, 2020, 22, 7170–7185]. We propose a new PXRD-based similarity index and comparison method (VC-PWDF, variable-cell powder difference) that substantially improves the agreement with COMPACK (2.84% total disagreement), compared to the CCDC packing similarity PXRD-based comparison tool (12.35%). By analysing the structure pairs for which COMPACK and VC-PWDF disagree, we evaluated the strengths and weaknesses of each method. COMPACK has a counter-intuitive dependence on its tolerance parameters, by which structures that are considered the same at a given tolerance are viewed as different at a looser tolerance. COMPACK's RMSD(N) can also increase with increasing tolerance values at fixed number of matching molecules (N). We demonstrated a few additional weaknesses of COMPACK: a) extremely costly or incorrect comparisons in molecules with highly-branched substituents (possibly due to its use of Ullmann's method), b) failure to match structures when the molecular connectivity is incorrectly determined, c) difficulties with molecules presenting helical chirality, and d) very large cluster sizes (up to 50 molecules) are sometimes needed to correctly identify unequal polymorphs. In turn, VC-PWDF has difficulty differentiating structures with similar packings, such as polytypes, and conformational and isomorphous phases. It is shown that the proposed VC-PWDF is at least as robust as COMPACK for comparing molecular crystal structures. Although a grey area of difficult-to-compare structures still exists, using both COMPACK and VC-PWDF in combination may be successful at narrowing it. [ABSTRACT FROM AUTHOR]

• Synthesis of novel nitrogen-rich purine-based heterocyclic compound. • Structural analysis through X-ray crystallography. • Multi-approach quantum mechanics (QM) analysis of noncovalent interactions. • Conceptual density functional theory (CDFT) study of chemical reactivity. • ADMET and in silico docking simulations on bioactivity behaviours. We introduce the synthesis and characterization of a novel purine derivative, 2-amino-6‑chloro-N,N-diphenyl-7H-purine-7-carboxamide. X-ray crystallography was utilized to elucidate its molecular and crystal structure. A comprehensive crystal packing analysis uncovered a network of diverse intermolecular interactions, including classical and unconventional hydrogen bonding. Remarkably, a unique halogen···π (C—Cl···π(ring)) interaction was identified and theoretically analyzed within a multi-approach quantum mechanics (QM) framework, revealing its lone-pair⋯π (n→π*) nature. Furthermore, insights into the electronic and chemical reactivity properties are provided by means of Conceptual Density Functional Theory (CDFT) at wB97X-D/aug-cc-pVTZ level. The compound's drug-likeness, pharmacokinetics, and toxicology profiles are assessed using ADMETlab 2.0. Finally, molecular docking simulations were conducted to evaluate its bioactivity as a potential cyclooxygenase-2 (COX-2) inhibitor. This study significantly advances our understanding of purine structure and reactivity, offering valuable insights for the development of targeted purine-based COX-2 inhibitors and anticancer therapeutics. [Display omitted] [ABSTRACT FROM AUTHOR]

Sufficiently high completeness of diffraction data is necessary to correctly determine the space group, observe solid-state structural transformations or investigate charge density distribution under pressure. Regrettably, experiments performed at high pressure in a diamond anvil cell (DAC) yield inherently incomplete datasets. The present work systematizes the combined influence of radiation wavelength, DAC opening angle and sample orientation in a DAC on the completeness of diffraction data collected in a single-crystal high-pressure (HP) experiment with the help of dedicated software. In particular, the impact of the sample orientation on the achievable data completeness is quantified and proved to be substantial. Graphical guides for estimating the most beneficial sample orientation depending on the sample Laue class and assuming a few commonly used experimental setups are proposed. The usefulness of these guides has been tested in the case of luminescent 1,3-diacetylpyrene, suspected to undergo transitions from the α phase (Pnma) to the γ phase (Pn21a) and δ phase (P1121/a) under pressure. Effective sample orientation has ensured over 90% coverage even for the monoclinic system and enabled unrestrained structure refinements and access to complete systematic extinction patterns.

Room‐temperature biological crystallography has seen a resergence in recent years and a collection of articles recently published in IUCrJ, Acta Cryst. D Structural Biology and Acta Cryst. F Structural Biology Communications, have been collected together to produce a virtual special issue at https://journals.iucr.org/special_issues/2022/RT/. [ABSTRACT FROM AUTHOR]

As the first step in the crystallization process, nucleation has been studied by many researchers. In this work, phenacetin (PHEN) was selected as a model compound to investigate the relationship between the solvent and nucleation kinetics. Induction times at different supersaturation in six solvents were measured. FTIR and NMR spectroscopy were employed to explore the solvent–solute interactions and the self-association properties in solution. Density functional theory (DFT) was adopted to evaluate the strength of solute–solvent interactions and the molecular conformations in different solvents. Based on these spectroscopy data, molecular simulation and nucleation kinetic results, a comprehensive understanding of the relationship between molecular structure, crystal structure, solution chemistry and nucleation dynamics is discussed. Both the solute–solvent interaction strength and the supramolecular structure formed by the self-association of solute molecules affect the nucleation rate. The findings reported here shed new light on the molecular mechanism of nucleation in solution.

An extensive characterization of [Ti(C22H18N2O6)]·H2O was performed by topological analysis according to Bader's quantum theory of atoms in molecules (QTAIM) from the experimentally (multipole model) and theoretically (DFT) determined electron density. To the best of our knowledge, this study is the first example of an experimental electronic structure of a coordination compound in which a peroxo anion is bonded to a 3d central atom. The titanium coordination polyhedron could be described as a deformed tetrahedral pyramid if the midpoint of the peroxide O—O bond (side-on mode) is considered to be in the quasi-apical position. According to the multipole model (MM) results, the titanium atom has a positive QTAIM charge of 2.05 e− which does not correspond to the formal Ti (IV) oxidation state. On the other hand, the peroxo oxygen atoms O(1) and O(2) have MM QTAIM charges of −0.27 and −0.12, respectively. This asymmetric charge density distribution on the peroxo oxygens is in agreement with the distorted orientation of the O2 moiety with respect to the titanium atom. Despite the fact that the overall MM charge of the O2 moiety is more remote from the formal −2 charge than from neutral O2, the O—O distance remains close to that in the peroxo O22− anion. In the case of DFT results, the titanium atom charge is also found to be close to +2, the O2x− moiety charge is around −1, the optimized O—O distance is shorter by only ca 0.04 Å than the experimental value of 1.5005 (16) Å, and the DFT d-populations on titanium are found to be lower than the experimental MM value. This study is the first experimental electronic structure of a transition metal peroxo complex.

This work reports reversible, single-crystal-to-single-crystal phase transitions of commensurately modulated sodium saccharinate 1.875-hydrate [Na(sac)(15/8)H2O]. The phases were studied in the temperature range 298 to 20 K. They exhibit complex disordered states. An unusual reentrant disorder has been discovered upon cooling through a phase transition at 120 K. The disordered region involves three sodium cations, four water molecules and one saccharinate anion. At room temperature, the structure is an eightfold superstructure that can be described by the superspace group C2/c(0σ20)s0 with q = (0, 3/4, 0). It demonstrates maximum disorder with the disordered chemical entities having slightly different but close to 0.50:0.50 disorder component ratios. Upon cooling, the crystal tends to an ordered state, smoothly reaching a unified disorder component ratio of around 0.90:0.10 for each of the entities. Between 130 and 120 K a phase transition occurs involving a sudden increase of the disorder towards the disorder component ratio 0.65:0.35. Meanwhile, the space group and general organization of the structure are retained. Between 60 and 40 K there is another phase transition leading to a twinned triclinic phase. After heating the crystal back to room temperature its structure is the same as before cooling, indicating a complete reversibility of the phase transitions.

Consider a projector matrix P, representing the first order reduced density matrix ρ1DETr,r′=2trPψrψ†r′ in a basis of orthonormal atom‐centric basis functions. A mathematical question arises, and that is, how to break P into its natural component kernel projector matrices, while preserving N‐representability of ρ1DETr,r′. The answer relies upon 2‐projector triple products, P′jPP′j. The triple product solutions, applicable within the quantum crystallography of large molecules, are determined by a new form of the Clinton equations, which—in their original form—have long been used to ensure N‐representability of density matrices consistent with X‐ray diffraction scattering factors. As such, the goal of this paper is to outline a possible pathway for the application of quantum crystallography to crystals of large molecular systems. [ABSTRACT FROM AUTHOR]

Among all possible NMR crystallography approaches for crystal‐structure determination, crystal structure prediction – NMR crystallography (CSP‐NMRX) has recently turned out to be a powerful method. In the latter, the original procedure exploited solid‐state NMR (SSNMR) information during the final steps of the prediction. In particular, it used the comparison of computed and experimental chemical shifts for the selection of the correct crystal packing. Still, the prediction procedure, generally carried out with DFT methods, may require important computational resources and be quite time‐consuming, especially if there are no available constraints to use at the initial stage. Herein, the successful application of this combined prediction method, which exploits NMR information also in the input step to reduce the search space of the predictive algorithm, is presented. Herein, this method was applied on mebendazole, which is characterized by desmotropism. The use of SSNMR data as constraints for the selection of the right tautomer and the determination of the number of independent molecules in the unit cell led to a considerably faster process, reducing the number of calculations to be performed. In this way, the crystal packing was successfully predicted for the three known phases of mebendazole. To evaluate the quality of the predicted structures, these were compared to the experimental ones. The crystal structure of phase B of mebendazole, in particular, was determined de novo by powder diffraction and is presented for the first time in this paper. [ABSTRACT FROM AUTHOR]

In the light of NASA's New Horizons mission, the solid-phase behaviour of methane and nitrogen has been re-examined and the thermal expansion coefficients of both materials have been determined over their whole solid temperature range for the first time. Neutron diffraction results indicate that the symmetric Pa3 space group is the best description for the α-nitrogen structure, rather than the long-accepted P213. Furthermore, it is also observed that β-nitrogen and methane phase I show changes in texture on warming, indicating grain growth.

Although a plethora of metal complexes have been characterized, those having multifunctional properties are very rare. This article reports three isotypical complexes, namely [Cu(benzoate)L2], where L = 4-styrylpyridine (4spy) (1), 2′-fluoro-4-styrylpyridine (2F-4spy) (2) and 3′-fluoro-4-styrylpyridine (3F-4spy) (3), which show photosalient behavior (photoinduced crystal mobility) while they undergo [2+2] cycloaddition. These crystals also exhibit anisotropic thermal expansion when heated from room temperature to 200°C. The overall thermal expansion of the crystals is impressive, with the largest volumetric thermal expansion coefficients for 1, 2 and 3 of 241.8, 233.1 and 285.7 × 10−6 K−1, respectively, values that are comparable to only a handful of other reported materials known to undergo colossal thermal expansion. As a result of the expansion, their single crystals occasionally move by rolling. Altogether, these materials exhibit unusual and hitherto untapped solid-state properties.

The data quality requirements for charge density studies on actinide compounds are extreme. Important steps in data collection and reduction required to obtain such data are summarized and evaluated. The steps involved in building an augmented Hansen–Coppens multipole model for an actinide pseudo-atom are provided. The number and choice of radial functions, in particular the definition of the core, valence and pseudo-valence terms are discussed. The conclusions in this paper are based on a re-examination and improvement of a previously reported study on [PPh4][UF6]. Topological analysis of the total electron density shows remarkable agreement between experiment and theory; however, there are significant differences in the Laplacian distribution close to the uranium atoms which may be due to the effective core potential employed for the theoretical calculations.

In this work, two methods of high-resolution X-ray data refinement: multipole refinement (MM) and Hirshfeld atom refinement (HAR) – together with X-ray wavefunction refinement (XWR) – are applied to investigate the refinement of positions and anisotropic thermal motion of hydrogen atoms, experiment-based reconstruction of electron density, refinement of anharmonic thermal vibrations, as well as the effects of excluding the weakest reflections in the refinement. The study is based on X-ray data sets of varying quality collected for the crystals of four quinoline derivatives with Cl, Br, I atoms and the -S-Ph group as substituents. Energetic investigations are performed, comprising the calculation of the energy of intermolecular interactions, cohesive and geometrical relaxation energy. The results obtained for experimentally derived structures are verified against the values calculated for structures optimized using dispersion-corrected periodic density functional theory. For the high-quality data sets (the Cl and -S-Ph compounds), both MM and XWR could be successfully used to refine the atomic displacement parameters and the positions of hydrogen atoms; however, the bond lengths obtained with XWR were more precise and closer to the theoretical values. In the application to the more challenging data sets (the Br and I compounds), only XWR enabled free refinement of hydrogen atom geometrical parameters, nevertheless, the results clearly showed poor data quality. For both refinement methods, the energy values (intermolecular interactions, cohesive and relaxation) calculated for the experimental structures were in similar agreement with the values associated with the optimized structures – the most significant divergences were observed when experimental geometries were biased by poor data quality. XWR was found to be more robust in avoiding incorrect distortions of the reconstructed electron density as a result of data quality issues. Based on the problem of anharmonic thermal motion refinement, this study reveals that for the most correct interpretation of the obtained results, it is necessary to use the complete data set, including the weak reflections in order to draw conclusions.

The investigation of molecular crystals at high pressure is a sought-after trend in crystallography, pharmaceutics, solid state chemistry, and materials sciences. The di-p-tolyl disulfide (CH3−C6H4−S−)2 system is a bright example of high-pressure polymorphism. It contains “conventional” solid–solid transition and a “hidden” form which may be obtained only from solution at elevated pressure. In this work, we apply force field and periodic DFT computational techniques to evaluate the thermodynamic stability of three di-p-tolyl disulfide polymorphs as a function of pressure. Theoretical pressures and driving forces for polymorphic transitions are defined, showing that the compressibility of the γ phase is the key point for higher stability at elevated pressures. Transition state energies are also estimated for α → β and α → γ transitions from thermodynamic characteristics of crystal structures, not exceeding 5 kJ/mol. The β → γ transition does not occur experimentally in the 0.0–2.8 GPa pressure range because transition state energy is greater than 18 kJ/mol. Relations between free Gibbs energy (in assumption of enthalpy) of phases α, β, and γ, as a function of pressure, are suggested to supplement and refine experimental data. A brief discussion of the computational techniques used for high-pressure phase transitions is provided.

Two new derivatives of calix[4]arene bearing on the upper rim 2-thiopenyl (Thicalix) or 2-pyridyl (Pycalix) Schiff-base substituents have been synthesised and characterised by IR, NMR, MS, and single crystal X-ray diffraction techniques. It was shown that the interaction of Thicalix with the copper(II) and palladium(II) ions is accompanied by hydrolysis of the azomethine bonds with subsequent oxidation of the aminophenolic fragment to diquinone Diquin, while the reaction of potassium tetrachloropalladate(II) with Pycalix results in the formation of metallocompex with 1:2 calix[4]arene/Pd(II) ratio. The single crystal X-ray diffraction analysis of Thicalix (1), the complex [(PdCl2)2(Pycalix)] (2) and Diquin (3) revealed that all compounds form molecular crystals as a result of numerous supramolecular interactions involving C − H···O, C − H···Cl, and C − H···π contacts. For 1 and 3 such interactions result in formation of dimers, while in 2 the dodecanuclear palladium aggregates composed of six calix[4]arene moieties are formed. [ABSTRACT FROM AUTHOR]

A hybrid discrete-continuous physical and mathematical model is used to study what deformation characteristics cause the rolling effect of C60 fullerene in a fullerite crystal. The interaction of fullerene atoms with surrounding molecules is described using a centrally symmetric interaction potential, in which the surrounding molecules are considered as a spherical surface of uniformly distributed carbon atoms. The rotational motion of fullerene is described by the Euler dynamic equations. The results of a numerical study of the influence of the rate, magnitude, and direction of strain on the dynamic characteristics of the rotational and translational motion of C60 fullerene in a crystalline fragment are presented.

This paper reports on the polymorphism of 2-propyl-1H-benzimidazole (2PrBzIm) induced by temperature change. Upon heating, an irreversible reconstructive-type phase transition at T = 384 K from the ordered form I (P212121) to a new polymorph, form IIHT (Pcam), was observed. The structural transformation between forms I and II involves significant changes in the crystal packing, as well as a key conformational variation around the propyl chain of the molecule. After the first irreversible phase transition, the IIHT form undergoes two further (reversible) phase transitions upon cooling at 361 K (IIRT) and 181 K (IILT). All three phases (forms IIHT, IIRT and IILT) have almost identical crystal packing and, given the reversibility of the conversions as a function of temperature, they are referred to as form II temperature phases. They differ, however, with respect to conformational variations around the propyl chain of 2PrBzIm. Energy calculations of the gas-phase conformational energy landscape of this compound about its flexible bonds allowed us to classify the observed conformational variations of all forms into changes and adjustments of conformers. This reveals that forms I and II are related by conformational change, and that two of the form II phases (HT and RT) are related by conformational adjustment, whilst the other two (RT and LT) are related by conformational change. We introduce the term `conformational phases' for different crystal phases with almost identical packing but showing changes in conformation.

The question of whether intermolecular interactions in crystals originate from localized atom...atom interactions or as a result of holistic molecule...molecule close packing is a matter of continuing debate. In this context, the newly introduced Roby–Gould bond indices are reported for intermolecular `σ-hole' interactions, such as halogen bonding and chalcogen bonding, and compared with those for hydrogen bonds. A series of 97 crystal systems exhibiting these interaction motifs obtained from the Cambridge Structural Database (CSD) has been analysed. In contrast with conventional bond-order estimations, the new method separately estimates the ionic and covalent bond indices for atom...atom and molecule...molecule bond orders, which shed light on the nature of these interactions. A consistent trend in charge transfer from halogen/chalcogen bond-acceptor to bond-donor groups has been found in these intermolecular interaction regions via Hirshfeld atomic partitioning of the electron populations. These results, along with the `conservation of bond orders' tested in the interaction regions, establish the significant role of localized atom...atom interactions in the formation of these intermolecular binding motifs.

In this study, the nature and characteristics of a short Br...π interaction observed in an ebselen derivative, 2-(2-bromophenyl)benzo[d][1,2]selenazol-3(2H)-one, has been explored. The electronic nature of this Br...π interaction was investigated via high-resolution X-ray diffraction and periodic density functional theory calculations using atoms-in-molecules (AIM) analysis. This study unravels the simultaneous presence of σ-hole and π-hole bonding characteristics in the same interaction. The dual characteristics of this unique Br...π interaction are further established via molecular electrostatic potentials (MESPs) and natural bond orbitals (NBOs).

Halogen bonds have emerged as noncovalent forces that govern the assembly of molecules in organic solids with a degree of reliability akin to hydrogen bonds. Although the structure-directing roles of halogen bonds are often compared to hydrogen bonds, general knowledge concerning the fundamental structural behavior of halogen bonds has had limited opportunity to develop. Following an investigation of solid-state reactions involving organic syntheses and the development of photoresponsive materials, this work demonstrates the ability of the components of intermolecular N...I halogen bonding – a `workhorse' interaction for the crystal engineer – to support a single-crystal-to-single-crystal [2+2] photodimerization. A comparison is provided of the geometric changes experienced by the halogen-bonded components in the single-crystal reaction to the current crystal landscape of N...I halogen bonds, as derived from the Cambridge Structural Database. Specifically, a linear-to-bent type of deformation of the halogen-bonded components was observed, which is expected to support the development of functional halogen-bonded materials containing molecules that can undergo movements in close-packed crystal environments.

The origin of unknown polymorphic phases within thin films is still not well understood. This work reports on crystals of the molecule terthiophene which were grown by thermal gradient crystallization using glass-plate substrates. The crystalline domains displayed a plate-like morphology with an extended lateral size of about 100 µm, but a thickness of only a few µm. Specular X-ray diffraction patterns confirmed the presence of a new polymorph of terthiophene. Crystal structure solution from a single crystal peeled from the film revealed a structure with an extremely large unit-cell volume containing 42 independent molecules. In contrast to the previously determined crystal structure of terthiophene, a herringbone packing motif was observed where the terminal ends of the molecules are arranged within one plane (i.e. the molecular packing conforms to the flat substrate surface). This type of molecular packing is obtained by 180° flipped molecules combined with partially random (disordered) occupation. A densely packed interface between terthiophene crystallites and the substrate surface is obtained, this confirms that the new packing motif has adapted to the flat substrate surface.

A mixed-valence conducting cation radical salt of the unsymmetrically substituted o-Me2TTF donor molecule (TTF is tetrathiafulvalene) was obtained upon electrocrystallization in the presence of the non-centrosymmetric NO3− anion. It crystallizes at room temperature in the monoclinic P21/c space group, with the anion disordered on an inversion centre. The donor molecules are stacked along the a axis. A 90° rotation of the longest molecular axis of o-Me2TTF generates a chessboard-like structure, preventing lateral S...S contacts between stacks and providing a strongly one-dimensional electronic system, as confirmed by overlap interaction energies and band structure calculations. A strong dimerization within the stacks explains the semiconducting behaviour of the salt, with σroom temp = 3–5 S cm−1 and Eactivated = 0.12–0.14 eV. An X-ray diffuse scattering survey of reciprocal space, combined with full structure resolutions at low temperatures (250, 85 and 20 K), evidenced the succession of two structural transitions: a ferroelastic one with an anion-ordering (AO) process and the establishment of a (0, ½, ½) superstructure below 124 (±3) K, also visible via resistivity thermal dependence, followed by a stack tetramerization with the establishment of a (½, ½, ½) superstructure below 90 (±5) K. The latter ground state is driven by a spin-Peierls (SP) instability, as demonstrated by the temperature dependence of the magnetic susceptibility. Surprisingly, these two kinds of instability appear to be fully decoupled here, at variance with other tetramethyltetrathiafulvalene (TMTTF) or tetramethyltetraselenafulvalene (TMTSF) salts with such non-centrosymmetric counter-ions.

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structure to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.

Direct observation and structural characterization of a kinetic product and a thermodynamic product for complexes with an NO2S2 macrocycle (L) are reported. L reacts with copper(I) iodide to give a mononuclear complex [Cu(L)]2(Cu2I4)·2CH2Cl2 (1), featuring three separate units. When cadmium(II) iodide was reacted with L, an anion-coordinated complex [Cd(L)I]2(Cd2I6)·4CH3CN (2) with a needle-type crystal shape was formed as the kinetic product. Interestingly, when the needle-type kinetic product was left undisturbed in the mother solution it gradually transformed to the pseudo-dimer complex [Cd2(L)2I2](Cd2I6) (3) with a brick-type crystal shape as the thermodynamic product. The dissolution–recrystallization process resulted in the elimination of the lattice solvent molecules (acetonitrile) in 2 and the contraction of two neighboring macrocyclic complex units [Cd(L)I]+, forming the pseudo-dimer 3 via an intermolecular Cd...I interaction between two monomers. For the entire process from kinetic to thermodynamic products, it was possible to obtain sequential photographic snapshots, single-crystal X-ray structures and powder X-ray diffraction patterns. For the copper(I) and cadmium(II) complexes, competitive NMR results agree with the solid-state data that show copper(I) has a higher affinity for L than does cadmium(II).

Fullerenes and cubane (C8H8) can be arranged to form heteromolecular crystals that exhibit interesting crystal phases. Experimental measurements indicate a rotor-stator phase for C60-cubane crystals in which the C60 molecules rotate freely whereas cubane molecules are essentially static. A similar phase is found for C70-cubane crystals but, due to C70's asymmetry, hindered rotations can be observed in specific crystal phases. Details of the rotational dynamics of the fullerenes in these heteromolecular crystals are difficult to be completely assessed by experiments. To this end, we have performed classical molecular dynamics simulations of C70-cubane crystals to investigate the behavior of C70 fullerenes and cubanes in the face-centered cubic and body-centered tetragonal crystallographic phases. Our simulations show that, in the cubic phase, C70 molecules are allowed to freely rotate whereas cubanes act as molecular bearings. In the tetragonal phase, the cubane molecules also remain practically fixed and the rotation of C70 fullerenes becomes hindered. In this phase, C70 molecules rotate around the fivefold axis, which in turn precesses about the c crystallographic direction of the unit cell. Details regarding the dynamics (e.g., energy barriers, reorientational relaxation processes, and phonon-libration coupling) of the C70 molecules in both crystal phases are discussed. In general, our results agree with previous experimental findings for C70-cubane crystals. [ABSTRACT FROM AUTHOR]

Using multiple computational tools, we examine five candidate crystal structures for β-carbonic acid, a molecular crystal of environmental and astrophysical significance. These crystals comprise of hydrogen bonded molecules in either sheetlike or chainlike topologies. Gas phase quantum calculations, empirical force field based crystal structure search, and periodic density functional theory based calculations and finite temperature simulations of these crystals have been carried out. The infrared spectrum calculated from density functional theory based molecular dynamics simulations compares well with experimental data. Results suggest crystals with one-dimensional hydrogen bonding topologies (chainlike) to be more stable than those with two-dimensional (sheetlike) hydrogen bonding networks. We predict that these structures can be distinguished on the basis of their far infrared spectra. [ABSTRACT FROM AUTHOR]

The propagation of shock waves normal to (111) in the energetic molecular crystal cyclotrimethylene trinitramine (RDX) has been studied using large-scale molecular dynamics simulations. Partial dislocation loops with Burgers vector 0.16[010] are nucleated homogeneously on (001) at Rankine–Hugoniot shock pressures greater than 1.3 GPa. Calculations of the [010] cross-section of the (001) generalized stacking fault energy surface as a function of applied pressure along [001] reveals that the stacking fault enclosed by the partial dislocation loops is rendered metastable by a stress-induced change in molecular conformation. Furthermore, large-scale molecular dynamics simulations performed on quasi-two-dimensional (111)-oriented single crystals show a two-wave elastic-plastic response with a “galloping” plastic wave. We propose that the onset of homogeneous dislocation nucleation accounts for the abrupt change in the elastic-plastic response of macroscopic (111)-oriented RDX single crystals observed in recent experiments by giving rise to an anomalous plastic hardening. [ABSTRACT FROM AUTHOR]

A microscopic theory is presented for piezoelectricity, electrostriction, and pyroelectricity in molecular crystals. The required coefficients are derived by combining a theoretical treatment of the dependence of molecular dipole moments on molecular displacement and a generalized elastic theory for internal strain. [ABSTRACT FROM AUTHOR]

We consider the process of establishing thermal equilibrium behind an ideal shock front in molecular crystals and its possible role in initiating chemical reaction at high shock pressures. A new theory of equilibration via multiphonon energy transfer is developed to treat the scattering of shock-induced phonons into internal molecular vibrations. Simple analytic forms are derived for the change in this energy transfer at different Hugoniot end states following shock compression. The total time required for thermal equilibration is found to be an order of magnitude or faster than proposed in previous work; in materials representative of explosive molecular crystals, equilibration is predicted to occur within a few picoseconds following the passage of an ideal shock wave. Recent molecular dynamics calculations are consistent with these time scales. The possibility of defect-induced temperature localization due purely to nonequilibrium phonon processes is studied by means of a simple model of the strain field around an inhomogeneity. The specific case of immobile straight dislocations is studied, and a region of enhanced energy transfer on the order of 5 nm is found. Due to the rapid establishment of thermal equilibrium, these regions are unrelated to the shock sensitivity of a material but may allow temperature localization at high shock pressures. Results also suggest that if any decomposition due to molecular collisions is occurring within the shock front itself, these collisions are not enhanced by any nonequilibrium thermal state. [ABSTRACT FROM AUTHOR]

We have studied the thermal behavior of orientationally disordered phase of caffeine molecular crystal using variable shape variable size Monte Carlo simulations in isothermal-isobaric ensemble. We have investigated the structure, especially the nature of orientational disorder of caffeine molecules as a function of temperature in the range of 400–550 K. Experimentally this system is known to undergo a phase transition at 426 K (considered to be an orientational order-disorder transition) and melt at 512 K. Our simulations reproduce these two transitions in excellent agreement with experiment. We find that the in-plane reorientational motion of molecules is restricted to small angles below 425 K, and above this temperature, molecules undergo essentially free rotations in molecular plane, and we find the melting to occur between 525 and 550 K. In the high temperature disordered phase, the disorder is mostly attributable to the in-plane orientational motion of the molecules. The potential energy profile for the in-plane reorientational rotation has six wells as a consequence of specific packing of molecules in the ab crystallographic plane. Also we find considerable out-of-plane reorientational disorder for the molecules in the high temperature disordered phase. We have also studied the structure and orientational disorder of the system that is quenched from 450 to 300 K. We find that in the quenched phase, the molecular orientational arrangement remains partially frozen. [ABSTRACT FROM AUTHOR]

The symmetry adapted cluster (SAC)/symmetry adapted cluster configuration interaction (SAC-CI) methodology for the ground, excited, ionized, and electron-attached states of molecules was extended to giant molecular systems. The size extensivity of energy and the size intensivity of excitation energy are very important for doing quantitative chemical studies of giant molecular systems and are designed to be satisfied in the present giant SAC/SAC-CI method. The first extension was made to giant molecular crystals composed of the same molecular species. The reference wave function was defined by introducing monomer-localized canonical molecular orbitals (ml-CMO’s), which were obtained from the Hartree-Fock orbitals of a tetramer or a larger oligomer within the electrostatic field of the other part of the crystal. In the SAC/SAC-CI calculations, all the necessary integrals were obtained after the integral transformation with the ml-CMO’s of the neighboring dimer. Only singles and doubles excitations within each neighboring dimer were considered as linked operators, and perturbation selection was done to choose only important operators. Almost all the important unlinked terms generated from the selected linked operators were included: the unlinked terms are important for keeping size extensivity and size intensivity. Some test calculations were carried out for the ring crystals of up to 10 000-mer, confirming the size extensivity and size intensivity of the calculated results and the efficiency of the giant method in comparison with the standard method available in GAUSSIAN 03. Then, the method was applied to the ring crystals of ethylene and water 50-mers, and formaldehyde 50-, 100-, and 500-mers. The potential energy curves of the ground state and the polarization and electron-transfer-type excited states were calculated for the intermonomer distances of 2.8–100 Å. Several interesting behaviors were reported, showing the potentiality of the present giant SAC/SAC-CI method for molecular engineering. [ABSTRACT FROM AUTHOR]

Spin-lattice and spin-spin-relaxation times, one- and two-dimensional spectra as well as two- and four-time correlation functions were measured for the molecular crystals ortho- and meta-carborane using deuteron nuclear magnetic resonance. It is found that in their noncubic phases these crystals exhibit highly anisotropic motions. In order to allow for a quantitative description of the motional geometry of the carboranes several stochastic models are formulated. By comparison of the model calculations with the experimental results it is found that the dynamics of these quasi-icosahedrally shaped molecules is governed by a composite reorientation process. Here the molecules perform threefold jumps around a molecule-fixed axis which itself can be tilted in four different directions with respect to a crystal-fixed axis. The tilt angle increases significantly with increasing temperature. On the basis of measurements of four-time stimulated-echo functions, implications for dynamic heterogeneity also in comparison with that of supercooled liquids are discussed. [ABSTRACT FROM AUTHOR]