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Organic molecular crystals constitute a class of materials of critical importance in numerous industries. Despite the ubiquity of these systems, our ability to predict molecular crystal structures starting only from a two-dimensional diagram of the constituent compound(s) remains a significant challenge. Most structure-prediction protocols require a customized interatomic interaction model on which the quality of the results can depend sensitively. To overcome this problem, we introduce a new topological approach to molecular crystal structure prediction. The approach posits that in a stable structure, molecules are oriented such that principal axes and normal ring plane vectors are aligned with specific crystallographic directions and that heavy atoms occupy positions that correspond to minima of a set of geometric order parameters. By minimizing an objective function that encodes these orientations and atomic positions, and filtering based on the vdW free volume and intermolecular close contact distributions derived from the Cambridge Structural Database, stable structures and polymorphs for a given crystal can be predicted entirely mathematically without reliance on an interaction model. Reliable prediction of the organic molecular crystal structures is critical across numerous industries yet remains a significant challenge. Here, the authors develop a mathematical workflow based on topological concepts that reduces solution time to mere hours. [ABSTRACT FROM AUTHOR]

We accelerate a key step in crystal structure prediction (CSP) using machine learning and report its robustness on a wide array of pharmaceutical molecules. The speedup achieved by our scheme allows for a scale-up in both the number of candidate drug molecules studied and the level of theory employed in their treatment, paving the way for tackling more complex crystal energy landscapes. [ABSTRACT FROM AUTHOR]

We report a simple synthesis of a new lead-free zero-dimensional (0D) hybrid halide compound, (5P1)InBr5·2H2O [(5P1) = NH3C6H12NH3], which hosts isolated and distorted octahedra of [InBr5(H2O)]2−, surrounded by bulky asymmetric organic cations [(5P1)2+] and H2O molecules. The hybrid crystals exhibit broad self trapped excitonic (STE) emission due to strong anharmonic soft structure. [ABSTRACT FROM AUTHOR]

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb2O5 with different crystal phases was studied. Nb2O5 particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb2O5 was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb2O5 spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb2O5 favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed. [ABSTRACT FROM AUTHOR]

The exploration of individual nanoclusters is rapidly advancing, despite stability concerns. To address this challenge, the assembly of cluster nodes through linker molecules has been successfully implemented. However, the linking of the cluster nodes itself introduces a multitude of possibilities, especially when additional factors come into play. While this method proves effective in enhancing material stability, the specific reasons behind its success remain elusive. In our laboratory, we have undertaken extensive studies on Ag cluster‐assembled materials. So, here our goal is to establish a model system that allows for the discernment of various factors, eliminating unnecessary complexities during the linking approach. So, we hope that the systematic discourse presented in here will contribute significantly to future endeavors, helping to set clear priorities, and provide solutions to concerns that arise when working with a model system. [ABSTRACT FROM AUTHOR]

A novel benzimidazole-1,2,3-triazole hybrid molecule, 4-(1H-benzo[d]imidazol-2-yl)-1-(2-methoxyphenyl)-1H-1,2,3-triazol-5-amine, was synthesized. Two concomitant polymorphs of the title compound were crystallized from the same solution simultaneously. Various quantum chemical methods were used to explain the formation of these polymorphic structures and predict their stability to external influence. Studying the possibility of changing the conformation by rotating aromatic rings around single bonds using the m06-2x/cc-pVTZ method and analyzing the molecular structure of the compound in the obtained crystal forms showed that the studied polymorphs differ in the conformation of the molecules. Both polymorphic structures have close lattice energies calculated in a plane wave approximation and energetic structures constructed using pairwise interaction energies. Two polymorphic forms can be classified as a columnar-layered packing of the dimeric building units. Quantum chemical modeling of the displacement of layers relative to each other allows us to state that both concomitant polymorphs are resistant to external mechanical influence. Thus, it can be assumed that the studied concomitant polymorphs were formed not due to kinetic and thermodynamic factors affecting the crystallization process, but due to the ability of two conformers with close energies to form crystals very similar in structure. [ABSTRACT FROM AUTHOR]

Materials exhibiting room temperature phosphorescence (RTP) have recently emerged as a subject of significant interest. In this study, we successfully created inclusion crystals by introducing halobenzenes as guests into a host molecule combining benzophenone with naphthalene diimide. This approach led to the creation of fascinating fluorescence and RTP properties dependent on the guest molecules. Notably, crystals containing chlorobenzene showed cyan fluorescence, while those with iodobenzene displayed red RTP. This difference highlights the impact of the guest molecule on the luminescent properties, with the significant external heavy‐atom effect of iodobenzene playing a key role in promoting efficient intersystem crossing between the excited singlet and triplet states. Crystals with bromobenzene exhibited a unique blend of fluorescence and RTP, both from benzophenone and naphthalene diimide, highlighting the moderate heavy‐atom effect. These findings reveal composite materials with remarkably diverse and interesting optical characteristics. [ABSTRACT FROM AUTHOR]

The supramolecular architectures of amide-containing compounds are highly dependent on the side-chain substituents, although the potential impact of isoxazole substituents on polymorph formation has not been thoroughly explored. Hence, three distinct forms of N1,N3-bis(5-methylisoxazol-3-yl)malonamide (1) were obtained and characterized: two polymorphic forms and one solvate. An in-depth analysis of the interactions and energy content of the crystals based on supramolecular clusters allowed us to propose crystallization mechanisms (crystal retrosynthesis). Specifically, the energy similarities between the interaction of the first sites NHamide⋯O＝Camide (form 1I) and the symmetric sites NHamide⋯Nisox (form 1II) were found to contribute to their formation. Nonetheless, the presence of DMSO resulted in the formation of form 1III, where the solvent molecule disrupted amide-amide interactions. The first nuclei are more stable than forms 1I and 1II. The compound of N1,N2-bis(5-methylisoxazol-3-yl)oxalamide (2) was used as a comparison, and through the absence of polymorphs, revealed that the central carbon in molecule 1 allows a flexible adaptation that leads to the three forms. These findings suggest that variations in solvents, flexibility, and the presence/absence of amide–amide interactions can modulate the competition between amide-containing isoxazole compounds. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis and characterization of seven different copper(II) coordination compounds, as well as the formation of a protonated ligand involving all compounds from the same reaction. Their synthesis required hydrothermal conditions, causing the partial in situ transformation of 5-fluoro uracil-1-acetic acid (5-FUA) into an oxalate ion (ox), as well as the protonation of the 4,4′-bipyridine (bipy) ligand through a catalytic process resulting from the presence of Cu(II) within the reaction. These initial conditions allowed obtaining the new coordination compounds [Cu2(5-FUA)2(ox)(bipy)]n·2n H2O (CP2), [Cu(5-FUA)2(H2O)(bipy)]n·2n H2O (CP3), as well as the ionic pair [(H2bipy)+2 2NO3−] (1). The mother liquor evolved rapidly at room temperature and atmospheric pressure, due to the change in concentration of the initial reagents and the presence of the new chemical species generated in the reaction process, yielding CPs [Cu(5-FUA)2(bipy)]n·3.5n H2O, [Cu3(ox)3(bipy)4]n and [Cu(ox)(bipy)]n. The molecular compound [Cu(5-FUA)2(H2O)4]·4H2O (more thermodynamically stable) ended up in the mother liquor after filtration at longer reaction times at 25 °C and 1 atm., cohabiting in the medium with the other crystalline solids in different proportions. In addition, the evaporation of H2O caused the single-crystal to single-crystal transformation (SCSC) of [Cu(5-FUA)2(H2O)(bipy)]n·2n H2O (CP3) into [Cu(5-FUA)2(bipy)]n·2n H2O (CP4). A theoretical study was performed to analyze the thermodynamic stability of the phases. The observed SCSC transformation also involved a perceptible color change, highlighting this compound as a possible water sensor. [ABSTRACT FROM AUTHOR]

This paper covers nineteen Pt(II) complexes of the composition Pt(η3-X1X2X3)(PR3), (X = N1, N2, N3; S1, S2, S3; or Te1, Te2, Te3). These complexes crystallized in three crystal classes: triclinic (eleven examples), monoclinic (six examples), and orthorhombic (two examples). Each tridentate ligand creates two metallocyclic rings with common N2, S2, or Te2 donor ligands of the types N1C2N2C2N3, N1C2N2NC2N3, S1C2S2C2S3, S1C3S2C3S3, and Te1CNTe2NCTe3. The homotridentate ligand with monodentate PR3 ligand builds up a distorted square planar geometry about Pt(II) atoms. The degree of distortion ranges from 0.029 to 0.092, and the reason for the distortion is discussed. There is an example that contains two crystallographically independent molecules within the same crystal. This is a classic example of distortion isomerism. [ABSTRACT FROM AUTHOR]

Crystals of the new trigonal borate Ва3Na0.9(OH)1.9[B9O16][B(OH)3] (sp. gr. P31c, a = 10.23684(15) Å, c = 8.72926(13) Å) were prepared by the mild hydrothermal synthesis. The filling of the channels in the framework of the polar nonaborate was found to differ from that determined previously. It is consistent with the main features of this structure type with the preservation of sassoline molecules in the channels. The structure contains an additional ОН group, which is involved in the coordination of Ва. [ABSTRACT FROM AUTHOR]

Crystals of the new trigonal borate Ва3Na0.9(OH)1.9[B9O16][B(OH)3] (sp. gr. P31c, a = 10.23684(15) Å, c = 8.72926(13) Å) were prepared by the mild hydrothermal synthesis. The filling of the channels in the framework of the polar nonaborate was found to differ from that determined previously. It is consistent with the main features of this structure type with the preservation of sassoline molecules in the channels. The structure contains an additional ОН group, which is involved in the coordination of Ва. [ABSTRACT FROM AUTHOR]

This report presents 'giant' and long-range premelting effects appearing in dielectric properties for the temperature and pressure paths of studies, with an explicit critical-like portrayal. The result was obtained for the 'classic' low molecular weight compound: nitrobenzene, tested in the solid and liquid phases. Dielectric studies enable the 'extraction' of the response from liquid layers between crystalline grains. Compressing increased the premelting effects, probably due to the 'crushing' of crystalline grains by isotropic squeezing and increasing the liquid layers between grains. This report indicates the significance of considering the melting/freezing phenomenon from the point of view of the 'solid crystalline grains and critical-type liquid layers in synergic interactions' concept. [ABSTRACT FROM AUTHOR]

Supramolecular aggregates featuring Se⋯N contacts have been identified in 88 crystals containing two, three or four selenium atoms, corresponding to 9% of crystals where Se⋯N contacts have the potential to form. Molecules with two selenium atoms make up the majority of examples (58) followed by molecules with three (12) and four (18) selenium atoms. A wide range of supramolecular aggregation patterns has been identified in the 88 crystals featuring Se⋯N contacts with one- (42%) and two- (31%) dimensional aggregation forming the majority compared with zero- (17%) and three- (10%) dimensional aggregation making up the rest. The overwhelming majority of Se⋯N contacts correspond to chalcogen-bonding interactions based on σ-hole interactions. Correlations in intermolecular separations were evident for isostructural crystals which showed that a comparable Te⋯N interaction was stronger than the equivalent Se⋯N interaction, and the Se⋯N interaction was always stronger than the equivalent S⋯N interaction. When compared to crystals of mono-nuclear selenium compounds, a very similar adoption rate was observed in their crystals but with a bias towards smaller aggregation patterns, i.e. 50, 44, 5 and 1% for zero-, one-, two- and three- dimensional, respectively. This observation is clearly consistent with the greater opportunity for multi-nuclear selenium molecules to form more interactions. However, as exemplified by the 18 tetra-nuclear molecules, not all selenium atoms participated in a Se⋯N contact as two, 10, two and four selenium atoms, out of a possible four, formed a Se⋯N contact in their crystals. [ABSTRACT FROM AUTHOR]

Co-crystallization of cyclic nitramines with sterically crowded molecules, i.e., ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20) with cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), is very difficult, but the co-agglomeration (slurry method) of their mixed micro-co-particles gives very good results. CL-20 is present in these co-agglomerates (CACs) in its β-form. Besides the medium of co-agglomeration, also the molar ratio is very important; it is possible to obtain β-CL-20/BCHMX (molar 1.8/1.0) with the impact sensitivity of 14.9 J. The density of these CACs approaches 99.6% of the density of the β-CL-20 crystals. Based on the application of the Raman, FTIR and PXRD techniques, it has been proved that the agglomeration of CL-20/BCHMX micro-co-particles leads to the formation of CACs mostly with the properties of co-crystals (CCs). This also seems to be confirmed by the relationships between the heat of formation and ring-deformation vibrations (in plane) and between the impact sensitivity and the difference in the asymmetric NO2 stretching vibrations in pure CL-20 and its CACs. The CACs studied have lower detonation energies than would be consistent with the percentage of individual coformers in these crystals. An examination of the most sensitive CACs (1.2 J) as a detonator primer has shown the absence of its required acceleration capabilities in the given detonator design. A comparison with literature data and our unpublished preliminary results indicates that the CACs and CCs of this type could have potential beneficial applications in propellants. [ABSTRACT FROM AUTHOR]

It is becoming evident that primary nucleation of crystals of organic molecules from solution is often anything but 'classical' in its complexity. It is also becoming increasingly clear that mesoscopic clusters of molecules are at least partly involved in the phenomenon. On-going advances are rapidly enabling these clusters to be investigated with ever more accuracy. However, despite numerous recent studies, fundamental knowledge of the properties, thermodynamics and kinetics of these clusters, and of their role in nucleation, is still limited. [ABSTRACT FROM AUTHOR]

The article titled "Ambiguous Faces of Water-Based Inclusion Compounds: L4(4)8(8) Intercalato-Clathrate Hydrate of Pt(II) Complex" explores the crystal structure of a PtII complex and its water layers that encapsulate guest molecules. The formation of these layers is driven by hydrophobic hydration and influenced by the size of the solute. The researchers compare this compound to similar water-based inclusion compounds to suggest parameters that characterize the corrugation of individual layers. The article provides more detailed information on this research and can be found in Chemistry - A European Journal. [Extracted from the article]

Fine-tuning of the ratio of two different states is important in controlling the structures and functions of crystalline materials. Here we report that clathrated guest molecules inside a tubular host crystal formed via halogen and hydrogen bonding exhibit reversible temperature-dependent orientational isomerisation in equilibrium. [ABSTRACT FROM AUTHOR]

A 3‐nm molecule comprising a cylindrical core and cross‐shaped rims was designed and synthesized by developing a modular synthetic route. By using a cyclic precursor from previous studies as a starting material, multiple carbazole units were installed at the rims of the defective cylinder. The defective cylinder was synthetically doped with two types of nitrogen atoms, that is, pyridinic and pyrrolic nitrogen atoms, which resulted in solvatochromic shifts in fluorescence by charge‐transfer interactions. The structure of the large, C552H496N24 molecule was fully disclosed by crystallographic analyses, and the unique helical arrangement of nitrogen‐doped cylinders in the crystal was revealed. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue is the group of Professor Bert Weckhuysen at Utrecht University. The image depicts the change in fluorescence color of a resorufin dye molecule when it is protonated and confined inside the micropores of zeolite‐β. Read the full text of the article at 10.1002/chem.202302553. [ABSTRACT FROM AUTHOR]

Orange (Cry-1O) and red (Cry-1R) emissive crystals with mechanical brittleness and elasticity, respectively, were obtained by modifying the crystallization conditions based on a green emissive molecule. The light transducing capability of Cry-1R in both the straight and bent states indicates the potential application of Cry-1R as an active optical waveguiding medium. [ABSTRACT FROM AUTHOR]

The computational prediction of atomistic structure is a long-standing problem in physics, chemistry, materials, and biology. Conventionally, force-fields or ab initio methods determine structure through energy minimization, which is either approximate or computationally demanding. This accuracy/cost trade-off prohibits the generation of synthetic big data sets accounting for chemical space with atomistic detail. Exploiting implicit correlations among relaxed structures in training data sets, our machine learning model Graph-To-Structure (G2S) generalizes across compound space in order to infer interatomic distances for out-of-sample compounds, effectively enabling the direct reconstruction of coordinates, and thereby bypassing the conventional energy optimization task. The numerical evidence collected includes 3D coordinate predictions for organic molecules, transition states, and crystalline solids. G2S improves systematically with training set size, reaching mean absolute interatomic distance prediction errors of less than 0.2 Å for less than eight thousand training structures — on par or better than conventional structure generators. Applicability tests of G2S include successful predictions for systems which typically require manual intervention, improved initial guesses for subsequent conventional ab initio based relaxation, and input generation for subsequent use of structure based quantum machine learning models. Accurate computational prediction of atomistic structure with traditional methods is challenging. The authors report a kernel-based machine learning model capable of reconstructing 3D atomic coordinates from predicted interatomic distances across a variety of system classes. [ABSTRACT FROM AUTHOR]

Crystals of [FeL2][BF4]2·nMeCN (L = N-(2,6-di{pyrazol-1-yl}pyrid-4-yl)acetamide; n = 1 or 2) and [FeL2][ClO4]2·MeCN are isomorphous. When n = 1 the compounds exhibit an abrupt, hysteretic spin-transition below 200 K, but when n = 2 the material remains high-spin on cooling. [FeL2]X2·EtCN (X− = BF4− or ClO4−) are isomorphous with the MeCN solvates and undergo their spin-transition at almost the same temperature. However this now occurs in two-steps via a re-entrant mixed-spin intermediate phase, which correlates with crystallographic ordering of the bent propionitrile molecule. [ABSTRACT FROM AUTHOR]

Luminescent small, all‐organic molecules are of tremendous interest in materials and life science applications. Nevertheless, targeted design requires a basic understanding of the excited state deactivation pathways of the molecules themselves, and the modulations of the processes that occur in the solid state. This particularly concerns crystalline molecular solids, as here not only solid‐state rigidification contributes to these modulations, but specific intermolecular interactions as well. Starting from the molecular properties, this work carefully disentangles all intramolecular and intermolecular factors to the radiative and nonradiative processes in crystalline all‐organic molecular solids to provide guidelines for targeted molecular materials design. [ABSTRACT FROM AUTHOR]

Ambient‐pressure trigonal phase α of selenourea SeC(NH2)2 is noncentrosymmetric, with high Z′ = 9. Under high pressure it undergoes several intriguing transformations, depending on the pressure‐transmitting medium and the compression or recrystallization process. In glycerine or oil, α‐SeC(NH2)2 transforms into phase β at 0.21 GPa; however in water, phase α initially increases its volume and can be compressed to 0.30 GPa due to the formation of α‐SeC(NH2)2·xH2O. The single crystals of α‐SeC(NH2)2 and of its partial hydrate α‐SeC(NH2)2·xH2O are shattered by pressure‐induced transitions. Single crystals of phase β‐SeC(NH2)2 were in situ grown in a diamond‐anvil cell and studied by X‐ray diffraction. The monoclinic phase β is centrosymmetric, with Z′ = 2. It is stable to 3.20 GPa at least, but it cannot be recovered at ambient conditions due to strongly strained NH...Se hydrogen bonds. No hydrogen‐bonding motifs present in the urea structures have been found in selenourea phases α and β. [ABSTRACT FROM AUTHOR]

Low-concentration alkali treatments at low temperatures facilitate the crystal transition of cellulose I to II. However, the transition mechanism remains unclear. Hence, in this study, we traced the transition using in situ solid-state 13C CP/MAS NMR, WAXS, and 23Na NMR relaxation measurements. In situ solid-state 13C CP/MAS NMR and WAXS measurements revealed that soaking cellulose in NaOH at low temperatures disrupts the intramolecular hydrogen bonds and lowers the crystallinity of cellulose. The dynamics of Na ions (NaOH) play a crucial role in causing these phenomena. 23Na NMR relaxation measurements indicated that the Na-ion correlation time becomes longer during the crystal transition. This transition requires the penetration of Na ions (NaOH) into the cellulose crystal and a reduction in Na-ion mobility, which occurs at low temperatures or high NaOH concentrations. The interactions between cellulose and NaOH disrupt intramolecular hydrogen bonds, inducing a conformational change in the cellulose molecules into a more stable arrangement. This weakens the hydrophobic interactions of cellulose, and facilitates the penetration of NaOH and water into the crystal, leading to the formation of alkali cellulose. Our findings suggest that a strategy to control NaOH dynamics could lead to the discovery of a novel preparation method for cellulose II. [Display omitted] [ABSTRACT FROM AUTHOR]

Disubstituted adamantanes having pyrogallol derivatives as V-shaped host molecules were synthesized to prepare complexes with carboranes, which are representative spherical guest molecules for macrocyclic compounds, including calixarenes and cyclotriveratrylenes. The crystallization of o-carborane (a) and 1,3-bis(3,4,5-trimethoxyphenyl)adamantane (1) in toluene resulted in the formation of inclusion crystals (1a) in a 1 : 1 ratio. X-ray crystallographic analysis revealed that two oxygen atoms in 1 interact with two hydrogen atoms of a through CH⋯O interactions to afford the complexes. In the case of 1,3-bis(3,4,5-triethoxyphenyl)adamantane (2), no inclusion crystal was obtained due to steric hindrance of the ethyl groups. Furthermore, the crystallization of 1 and a benzoquinone derivative (b) provided reddish crystals (1b) with a 1 : 2 host : guest complexation stoichiometry, where lone pair⋯π interactions in the complexes were observed in addition to donor–acceptor interactions. [ABSTRACT FROM AUTHOR]

Crystalline porous solids based on molecules with intrinsic porosities are a diverse group of materials that have been investigated in the context of adsorption-based separations and other applications. Novel computational approaches are being developed to identify structures with desired properties by sieving through large sets of candidates. Recently, both in silico synthesis of new porous molecular species and identification of alike in large molecular databases have become possible. However, assessing the porosity of the corresponding crystalline materials has been based on performing crystal structure prediction (CSP), followed by the characterization of the porosity of the resulting phases. CSP has a significant computational cost, which seriously limits the possibility of high-throughput computational screening applications. Herein, we present an avenue to circumvent the need for CSP for every investigated molecular structure by introduction of molecular-based crystalline material porosity estimators. In particular, our analysis of previously-reported crystalline porous materials involving porous molecules uncovered the correlations between the molecular porosity descriptors and the porosity descriptors of the corresponding crystalline phases. We exploit these correlations by building random forest classifiers and regressors to estimate the material porosity based on the structure of its porous molecular building block. [ABSTRACT FROM AUTHOR]

The design of molecular compounds that exhibit flexibility is an emerging area of research. Although a fair amount of success has been achieved in the design of plastic or elastic crystals, realizing multidimensional plastic and elastic bending remains challenging. We report herein a naphthalidenimine–boron complex that showed size‐dependent dual mechanical bending behavior whereas its parent Schiff base was brittle. Detailed crystallographic and spectroscopic analysis revealed the importance of boron in imparting the interesting mechanical properties. Furthermore, the luminescence of the molecule was turned‐on subsequent to boron complexation, thereby allowing it to be explored for multimode optical waveguide applications. Our in‐depth study of the size‐dependent plastic and elastic bending of the crystals thus provides important insights in molecular engineering and could act as a platform for the development of future smart flexible materials for optoelectronic applications. [ABSTRACT FROM AUTHOR]

A crystalline rhombic dodecahedral shape with a size up to 23.7 μm via the self-assembly of a C3-symmetric triaminoguanidinium derivative has been reported. Structural evidence confirms the preferential occupancy of the solvent molecules in the (110) crystal facet over (100), favouring the growth direction for realizing such morphology. [ABSTRACT FROM AUTHOR]

The growth of spontaneously twisted crystals is a common but poorly understood phenomenon. An analysis of the formation of twisted crystals of a metastable benzamide polymorph (form II) crystallizing from highly supersaturated aqueous and ethanol solutions is given here. Benzamide, the first polymorphic molecular crystal reported (1832), would have been the first helicoidal crystal observed had the original authors undertaken an analysis by light microscopy. Polymorphism and twisting frequently concur as they are both associated with high thermodynamic driving forces for crystallization. Optical and electron microscopies as well as electron and powder X‐ray diffraction reveal a complex lamellar structure of benzamide form II needle‐like crystals. The internal stress produced by the overgrowth of lamellae is shown to be able to create a twist moment that is responsible for the observed non‐classical morphologies. [ABSTRACT FROM AUTHOR]

Nitrogen has unique bonding ability to form single, double, and triple bonds, similar to that of carbon. However, a molecular crystal formed by an aromatic polynitrogen similar to a carbon system has not been found yet. Herein, a new form of stable all‐nitrogen molecular crystals consisting of only bispentazole N10 molecules with exceedingly high energy density is predicted. The crystal structures and the conformation of N10 molecules are strongly correlated, both depending on the applied external pressure. These molecular crystals can be recovered upon the release of the pressure. The first‐principles molecular dynamics simulations reveal that these all‐nitrogen materials decompose at temperatures much higher than room temperature. The decompositions always start from breaking off N2 molecules from the nitrogen ring and can release a large amount of energy. These new polynitrogens are aromatic and are more stable than all the other polynitrogen crystals reported previously, providing a new green strategy to get all‐nitrogen, nonpolluting high energy density materials without introducing any metal or other guest stabilizer. [ABSTRACT FROM AUTHOR]

Nitrogen has unique bonding ability to form single, double, and triple bonds, similar to that of carbon. However, a molecular crystal formed by an aromatic polynitrogen similar to a carbon system has not been found yet. Herein, a new form of stable all‐nitrogen molecular crystals consisting of only bispentazole N10 molecules with exceedingly high energy density is predicted. The crystal structures and the conformation of N10 molecules are strongly correlated, both depending on the applied external pressure. These molecular crystals can be recovered upon the release of the pressure. The first‐principles molecular dynamics simulations reveal that these all‐nitrogen materials decompose at temperatures much higher than room temperature. The decompositions always start from breaking off N2 molecules from the nitrogen ring and can release a large amount of energy. These new polynitrogens are aromatic and are more stable than all the other polynitrogen crystals reported previously, providing a new green strategy to get all‐nitrogen, nonpolluting high energy density materials without introducing any metal or other guest stabilizer. [ABSTRACT FROM AUTHOR]

An approach to constructing semiempirical equations of state of molecular crystals of nitro compounds is suggested allowing one to describe isothermal compression of the crystal of triaminotrinitrobenzene (1,3,5-triamino-2,4,6- trinitrobenzene) by the familiar modulus of three-dimensional compression and sublimation heat of the crystal obtained from experiments not related to isothermal compression. A comparative analysis of experimental data on isothermal compression of the molecular crystal of triaminotrinitrobenzene and calculations by the proposed equation of state have shown that the experimental and calculated values of pressure are within the limits of experimental uncertainty. [ABSTRACT FROM AUTHOR]

Combining first-principles calculations and non-Condon charge transfer rates proposed by us recently [Y. Zhao and W. Z. Liang, J. Chem. Phys. 130, 034111 (2009)], we investigated non-Condon effect on charge carrier mobility of organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF) crystal. The first-principles results reveal that only several high-frequency intramolecular vibrational modes dominate the reorganization energy, and the nuclear-coordinate dependence of electronic coupling prefers to perform an exponential or Gaussian property for most intermolecular modes rather than a linear one as assumed in conventional models. Furthermore, the electronic coupling of an isolated DT-TTF dimer is indeed affected by the surrounding molecules. The predicted non-Condon mobilities with use of the obtained structure parameters are always greater than those from Condon approximation, and the non-Condon dynamic disorder is not important for DT-TTF, which is also confirmed by molecular dynamics simulation. More interestingly, the bandlike property can be predicted under the hopping mechanism when the nuclear tunneling is incorporated. [ABSTRACT FROM AUTHOR]

Fatty acids constitute one of the main components of the lipid lamellae in the top layer of the skin, known as the stratum corneum, which acts as a barrier to foreign substances entering the body and to water leaving the body. To better understand the mechanics of the skin, a molecular-level understanding of the structure of the lamellae needs to be investigated. As a first step toward this goal, the current work involves the development of a coarse-grained model for fatty acids in an amorphous and a crystalline state. In order to retain the structural details of the atomistic molecules, radial distribution functions have been used to provide target data against which the coarse-grained force field is optimized. The optimization was achieved using the method developed by Reith, Pütz, and Müller-Plathe with a damping factor introduced into the updating scheme to facilitate the convergence against the crystalline radial distribution functions. Using this approach, a transferable force field has been developed for both crystalline and amorphous systems that can be used to describe fatty acids of different chain lengths. We are unaware of any other coarse-grained model in the literature that has been developed to study solid phases. Additionally, the amorphous force field has been shown to accurately model mixtures of different free fatty acids based on the potentials derived from pure lipid systems. [ABSTRACT FROM AUTHOR]

The hindered rotational states of molecules confined in crystal fields of octahedral symmetry, and their time-dependent alignment obtained by pulsed nonresonant laser fields, are studied computationally. The control over the molecular axis direction is discussed based on the evolution of the rotational wave packet generated in the cubic crystal-field potential. The alignment degree obtained in a cooperative case, where the alignment field is applied in a favorable crystal-field direction, or in a competitive direction, where the crystal field has a saddle point, is presented. The investigation is divided into two time regimes where the pulse duration is either ultrashort, leading to nonadiabatic dynamics, or long with respect to period of molecular libration, which leads to synchronous alignment due to nearly adiabatic following. The results are contrasted to existing gas phase studies. In particular, the irregularity of the crystal-field energies leads to persistent interference patterns in the alignment signals. The use of nonadiabatic alignment for interrogation of crystal-field energetics and the use of adiabatic alignment for directional control of molecular dynamics in solids are proposed as practical applications. [ABSTRACT FROM AUTHOR]

The interaction energy and minimum energy structure for different geometries of the benzene dimer have been calculated using the recently developed nonlocal correlation energy functional for calculating dispersion interactions. The comparison of this straightforward and relatively quick density functional based method with recent calculations provides a promising first step to elucidate how the former, quicker method might be exploited in larger more complicated biological, organic, aromatic, and even infinite systems such as molecules physisorbed on surfaces and van der Waals crystals. [ABSTRACT FROM AUTHOR]

We have investigated the dynamics of ferrocene in the channels of single crystals of AlPO4-5, using nuclear forward scattering. Around 150 K, rotational dynamics sets in, which is strongly anisotropic up to 235 K. Assuming planar rotation of the ferrocene molecules within the channels we obtained an activation energy of (8.2±1.0) kJ mol-1. Between 235 K and room temperature, the rotation becomes isotropic. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In search of low-energy excitations in rigid molecular crystals, the available heat capacity, C[sub p], data of 85%C[sub 60]–15%C[sub 70] (wt %) mixture at temperatures in the 2–30 K range have been analyzed. It is found that its C[sub p]/T[sup 3] against T plot has an asymmetric peak centered at 4.5 K, which has the features of both the Boson peak and of the peak attributed to librations of guest molecules in clathrates. Appearance of a peak in the C[sub p]/T[sup 3] against T plot is a characteristic of the Einstein equation for random phase atomic motions. Most of the C[sub p] of fullerenes at T<10 K is attributed to random phase librations of C[sub 60] and C[sub 70] molecules at their crystal sites. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rotational dynamics of a nondipolar solute, 2,5-dimethyl-1,4-dioxo-3, 6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and a dipolar solute, coumarin 6 (C6) has been studied in the isotropic phase of a liquid crystal, 4′-methoxybenzylidene-4-n-butylaniline (MBBA) to understand the influence of pseudonematic domains on the dynamics of dopant molecules. The reorientation times of both DMDPP and C6 follow the Stokes–Einstein–Debye hydrodynamic model instead of the Landau–de Gennes model, which is used to describe the rotational relaxation of neat isotropic liquid crystals. However, comparison of the data for both DMDPP and C6 in MBBA to that in an isotropic solvent, 1-decanol reveals that the probes are rotating considerably slower in the liquid crystal. These results indicate that ordered local structures of the liquid crystal exert more friction on the rotating solute molecule compared to an isotropic liquid. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Chirality of optically active liquid crystal molecules has become an important research topic and the subject of a number of theoretical and experimental studies. We present here the results of the application of a newly developed scaling method of a chiral index to a range of chiral molecules. Good agreement is found between the scaled chiral index and the helical twisting power for relatively rigid molecules. Two flexible TADDOL (α, α, α', α'-tetraaryl-1,3-dioxolan-4,5-dimethanol) molecules are studied to determine which conformations may give rise to their high experimental helical twisting powers. A variety of links between the moment of inertia tensor, the dihedral angles, the scaled chiral indices, the minimum energy of the optimized geometry and the experimental helical twisting power are discussed. The scaled chiral and steric indices and dihedral angles are promising as predictors of experimental helical twisting power, in particular for relatively rigid molecules, in cases where all the relevant interactions are determined by the molecular structure. [ABSTRACT FROM AUTHOR]

The stream of photons emitted by a single quantum system such as a molecule or a nanocrystal is often statistically characterized by the distribution of delays between consecutive photons, or by the autocorrelation function of the intensity, or by the distributions of on- and off-times. We derive and discuss general relations between their Laplace transforms, addressing the influence of detection yield and background. Our analytical treatment applies to any distribution of delays and to random telegraph signals, including nonexponential distributions. We examine the special case of systems switching between two states characterized by different distributions of delays, where the switching can obey various statistics. We show that the second-order autocorrelation function keeps track of long-time fluctuations which are obviously lost in averaging the distributions of delays. We apply our formalism to random telegraphs, in particular to those with power-law distributions of onand/or of off-times, which are encountered in the blinking of single semiconductor nanocrystals. [ABSTRACT FROM AUTHOR]

To directly observe the behavior of single molecules in real time and space, the x-ray methodology, diffracted x-ray tracking, has been proposed. This system monitors the spots of a diffracted x ray from individual nanocrystals, which are labeled with the individual single molecules. To operate single molecular detection systems with x rays, it is necessary to fabricate dispersive nanocrystals and observe the diffracted spots from the nanocrystals. We succeeded in fabrications of dispersive one-dimensional (Mo/Si) nanocrystals with diameters of approximately 25 nm using reactive ion etching. Furthermore, we monitored well-defined diffracted x-ray spots from Mo/Si nanocrystals (2.5 bilayers: Mo/Si/Mo/Si/Mo, d-space = 5.0 nm) in real time (2.0 ms). [ABSTRACT FROM AUTHOR]

Proposes a method to calculate the free energy of a crystal of rigid molecules. Application of the method to the ice phase of the TIP4P model for H[sub 2]O; Calculation of the free energy of the liquid and gas phases; Details of the molecular dynamics simulation.

Transient self‐assembling systems often suffer from accumulation of chemical wastes that interfere with the formation of pristine self‐assembled products in subsequent cycles. Herein, we report the transient crystallization of a cucurbit[8]uril‐based host‐guest complex, preventing the accumulation of chemical wastes. Base‐catalyzed thermal decarboxylation of trichloroacetic acid that chemically fuels the crystallization process dissolves the crystals, and produces volatile chemical wastes that are spontaneously removed from the solution. With such self‐clearance process, no significant damping in the formation of the crystals was observed. The morphology and structural integrity of the crystals was also maintained in subsequent cycles. The concept may be further extended to obtain other temporally functional materials, quasicrystals, etc. based on stimuli‐responsive guest molecules. [ABSTRACT FROM AUTHOR]