A bis(acetylacetonato-O,O′)(imidazole)nitrocobalt(III) coordination compound was synthesized and characterized toward photoswitching properties. The compound exists as two isomers, cis and trans, depending on the relative arrangement of the two acetylacetone ligands chelating the metal center. Crystals of both isomers were obtained. The cis form was proven to be photoswitchable in the solid state at room temperature and also to a lesser extent at lower temperatures down to 10 K, upon near-UV irradiation (365–405 nm LED light). Based on the IR spectroscopic results, the photo-reaction is very efficient under ambient conditions with the maximum nitro-to-nitrito conversion reaching ca. 80%. The reaction is reversible. The photo-induced isomer is stable at 100 K, whereas at room temperature, full sample relaxation is observed 7 h after irradiation. Photocrystallographic experiments indicated the formation of the exo-nitrito isomer under continuous illumination of the sample with the 405 nm LED light at room temperature. The achieved conversion amounted to around 60%. In turn, the trans analogue does not exhibit photoswitching properties under such conditions. The experimental solid-state spectroscopic and X-ray diffraction results were supported by theoretical modeling and physicochemical analyses. The differences in photoactivity of the examined cis and trans isomers of the studied compound in the solid state can be explained based on steric and energetic factors.

The rational design and control of crystal structures of organic semiconductors remain critical challenges in the development of superior organic semiconductors, yet few studies have focused on these topics. In the present work, we demonstrate that the methylthiolation of acenes at the peri-positions of the terminal benzene rings is a rational and possibly general approach to realize the rubrene-like pitched π-stacking structure. Among the newly synthesized anthracene and tetracene derivatives, bis(methylthio)anthracene, bis(methylthio)tetracene, and tetrakis(methylthio)tetracene (1, 3, and 4), but not tetrakis(methylthio)anthracene (2), were found to have pitched π-stacking crystal structures. Hirshfeld surface analysis of these crystal structures, in comparison with the parent anthracene and tetracene crystal structures, revealed that the methylthiolation effectively disrupts the CH−π interactions in the parent system and induces the π-stacking. The analysis of the crystal structures of the corresponding chlorinated anthracenes and tetracenes revealed that, although the chlorination of acenes similarly disrupts the CH−π interactions and induces π-stacking, the resulting crystal structures significantly differ from those of 1–4. The results of natural bond orbital analysis highlight the active role of the methylthio groups of 1–4 in inducing the pitched π-stacking structures via attractive intermolecular interactions through S–H intermolecular interactions. The observed effects of the methylthio groups, which were regioselectively introduced to acenes, will help guide the design of organic semiconductors with controlled crystal structures.

Natural gas purification and biogas recovery require efficient separation of CO2 from CH4, as CH4 is increasingly being recognized as a promising substitute for petroleum due to its environmentally sustainable nature, abundance in natural resources, and economic benefits. In the present work, a 3D Cd-based metal–organic framework, [Cd2(DBrTPA)2(DMF)3] (MUT-11) 2,5-[dibromoterephthalic acid (DBrTPA) and dimethyl formamide (DMF)] was synthesized using a combination of different synthetic methods and fully characterized via several techniques. Additionally, a variety of organic solvents were employed to perform the solvent stability test. The MUT-11 structure was subjected to Grand Canonical Monte Carlo and molecular dynamics simulations to study the adsorption characteristics of CO2 and CH4 gases in both pure and binary states. The results acquired through the simulation-based analysis revealed that the adsorption of CO2 is dominant in all pressure and temperature conditions.

The drug/(PEG/γ-CD-PPRX) complex is a unique multicomponent supramolecular structure where the drug molecules are incorporated in the intermolecular spaces of the polypseudorotaxane (PPRX) prepared from polyethylene glycol (PEG) and γ-cyclodextrin (γ-CD). Herein, we report a sealed-heating preparation method to obtain an unanticipated polymorphic form of the drug/(PEG/γ-CD-PPRX) complex, which is the hexagonal-columnar (HC) form. The encapsulation efficiency of the six guest drugs was evaluated. The crystalline structural changes and the guest encapsulation monitored by powder X-ray diffraction revealed that a low sealed-heating temperature with a small amount of water was the optimal preparation condition for obtaining the HC form complex. The solution-state 1H nuclear magnetic resonance measurement demonstrated that stoichiometric complexation was dependent on the cross-sectional area of the guest drug molecule. However, stoichiometric complexation could not be achieved with all guest drugs, and the encapsulation efficiency was found to be governed by the guest drug properties, such as vapor pressure and molecular size. The findings of this study would contribute to understanding the complexation behavior of guest molecules in multicomponent supramolecular complexes and offer new insights into the fabrication of novel ordered supramolecular structures.

Three isomers of an arylpiperazine derivative with different positioning of the amide group to the labile alkyl chain, showing varied affinity to the serotonin 5-HT1A receptor, are discussed. Using experimental studies (X-ray, NMR, and ssNMR), quantum chemical calculations (for gaseous and solid phases), and modern cheminformatics methods, the molecular and crystal structures of three regioisomers (ortho, meta, and para) were meticulously analyzed. The results showed that for the best activity, the proper positioning of the hydrogen bond active group is essential, the energy of the H-bonds, and the propensity to aromatic interactions. Crystal data, although the best tool for obtaining knowledge about the spatial distribution of active molecular fragments, most often refers to one point in space determined by the number of degrees of freedom of the molecule. In order to recognize other conformations, e.g., when performing simulations of receptor–ligand complexes, it is worth applying modern knowledge-based methods using big data (in this case, crystallographic databases). In the discussed case, the conformation of the ortho isomer found in the crystal and in the previously performed docking studies differs in terms of the amide group orientation. We were curious if we could explain this observation by analyzing the molecular and crystal structures in detail. Our studies have shown that the ortho isomer conformation in the crystal might not be optimal, and the observed intramolecular hydrogen bond with an estimated energy of approximately 30 kJ/mol, poorly represented in the entire Cambridge Structural Database, can be easily broken in a protein environment. In the crystal, this isomer forms the weakest intermolecular interactions. In comparison, the least active para isomer molecule is too prolate and creates the strongest intermolecular H-bonds between amide fragments, although the geometry of these interactions is statistically unusual. On the other hand, the meta isomer, the best of the ligands, shows medium asphericity and creates the most effective intermolecular interactions in the crystal and in the modeled ligand–receptor complex.

The thermodynamics of partitioning of an organic structure-directing agent (OSDA) between water and an organic solvent such as chloroform or trichloroethane serve as a proxy for energetic interactions during zeolite synthesis. Using several newly synthesized OSDAs, we have extended our earlier calorimetric and partitioning studies of the thermodynamics of transfer to separate effects of charge (C/N+ ratio) and structure in a series of structurally related OSDAs. The Gibbs free energies of transfer are close to zero, resulting from a balance of strongly exothermic and relatively similar enthalpies and strongly negative and relatively similar entropies of transfer. There is no obvious correlation between the thermodynamics of transfer and the efficacy of a given OSDA in the zeolite synthesis. One must conclude that with bulk energetics of transfer being similar in most cases studied, the critical factors in OSDA function in zeolite synthesis are kinetically rather than thermodynamically controlled and arise from differences in activation energies related to details of OSDA structure and interactions during nucleation of possible zeolite precursors.

Dotinurad, a novel selective urate reabsorption inhibitor, was studied for preformulation beneficiation by supramolecular methods. Two polymorphic forms (form I, form II), a monohydrate, and four solvates were prepared and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis, which enabled the respective molecular conformation, intermolecular interactions, and packing arrangements to be determined. Combined with Hirshfeld surface analysis and energy networks, the stability and conformations of the above seven solid forms were studied by thermal analysis, crystal structure, and experimental results of solvent-mediated transitions and heat-treated transitions. Interestingly, form I and five solvates were transformed to form II under solvent suspension easily and quickly. The desolvation of DT solvates resulted in form II, which is mainly related to the hydrogen bonds between DT molecules and solvents.

Three FeIII-MI heterometallic complexes with anions of cyclobutane-1,1-dicarboxylic acid (H2cbdc) dianions [MIFe(cbdc)2(H2O)2]n (MI = Na (1), Rb (2) or Cs (3)) were obtained, with the compounds being two-dimensional (2D)-coordination polymers built of bischelate moieties {Fe(cbdc)2(H2O)2}− bound with alkali metal ions. In 1, the two coordinated water molecules are in the cis-position, while in 2 and 3 they are in the trans-position. The DC magnetic data and ab initio calculations demonstrate that Fe3+ ions in 1 possess a negative D value, while those in 2 and 3 have a positive D value. The easy-axis anisotropy found for 1 is a rare example for Fe3+ ions. A topological analysis of the compounds synthesized and a series of known mononuclear octahedrally coordinated Fe3+ complexes (from Cambridge Structural Database) that are interconnected into a crystal structure by alkali metal cations in a way similar to complexes 1–3 was carried out.

Copper joints have replaced solder interconnects in integrated circuits due to their great electrical properties and lower-temperature processing. To isolate Cu from oxidizing during bonding processes, a (111)-oriented nanotwinned Ag (NT-Ag) thin layer was electroless-deposited on a (111)-oriented NT-Cu film. Such a method outperforms the sputtering approach in terms of expenditure, environmental impact, and deposition rate. The microstructures of the Ag films were then analyzed. Results show that columnar NT-Ag grains epitaxially grew along the columnar NT-Cu grains. Additionally, two types of joints (Cu–Ag and Ag–Ag) were fabricated and characterized. We found that the bonding strength of the Cu–Ag joints was higher than that of the Ag–Ag joints. This could be attributed to the greater diffusion rate of Ag atoms in Cu than the self-diffusion of Ag.

Studying weak intermolecular interactions in molecular crystals is key to a better understanding of crystalline polymorphism and structure formation principles. Dibenzyldiphenylsilane (1) was synthesized as a hydrocarbon-patterned molecular model compound. Three polymorphic crystal structures, one with Z′ = 1 (1-t, triclinic, P1̅), one with Z′ = 2 (1-o, orthorhombic, Pna21), and another with Z′ = 4 (1-m, monoclinic, Pc), were analyzed by single-crystal X-ray diffraction analysis. Subtle differences in the weak intermolecular interactions between the three polymorphic crystal packing arrangements were thoroughly investigated by Hirshfeld surface analysis along with two-dimensional fingerprint plots. The highest Z′ polymorph (1-m) has the lowest packing density but exhibits the shortest intermolecular H···H and C–H···π contacts. Conformational differences and the contribution of dispersion interactions to the stability of the three polymorphic crystal structures were investigated by means of density functional theory (DFT) calculations, comparing different functionals. The Z′ > 1 polymorphs undergo phase transitions into the triclinic form 1-t (Z′ = 1) at room temperature.

With the perspective of using two-dimensional materials as growth substrates for semiconductors, we explore the nucleation of GaN nanostructures on graphene. Using plasma-assisted molecular beam epitaxy, we investigate what happens during the long incubation time which precedes the epitaxy of the first GaN islands. After 30 min of nitrogen plasma exposure with no deposition, we find that graphene is modified, and we identify C–N bonds. We measure and model the variation of the incubation time with the growth parameters. These data support the idea that graphene must be modified before GaN nucleation becomes possible. We then test the adhesion at the interface between graphene and the GaN nanostructures. Our studies converge on the conclusion that GaN nanostructures nucleate on graphene from pyridinic N atoms incorporated in the lattice, which are responsible for strong binding between the two materials.

There is a growing consensus that numerous crystallization processes occur via a ”nonclassical” mechanism, that is, involve transient noncrystalline structures (molecular clusters, solid nanoparticles, liquid nanodroplets, etc.). Because these transient noncrystalline structures have been so far overlooked in chemical engineering approaches, their impact on reactor-scale models of precipitation processes still needs assessment. Here we show that standard incubation-counting methods underestimate nucleation rates of cerium oxalate by 1 to more than 3 orders of magnitude at concentrations between 1 and ca. 100 mmol L–1. Because the transient nanoparticles and nanodroplets have lifetimes in the 100 ms to 100 s range, it becomes impossible to choose a priori an incubation time that allows complete crystallization without aggregation or ripening. This discrepancy calls for a revision of databases of nucleation rates, using instead in situ, time-resolved techniques with resolutions at the nanometer scale able to count and discriminate between crystals and noncrystalline objects, such as X-ray scattering used in this report.

Organic cocrystals based on H-bonding as well as π-stacking interactions between 4,4′-bipyridine–pyromellitic acid (1) and 4,4′-bipyridine–phthalic acid (2) are reported. Cocrystals 1 and 2 were fully characterized by single-crystal X-ray diffraction and NMR and IR spectroscopy. The single-crystal X-ray diffraction shows the H stacking pattern of the adjacent 4,4′-bipyridine molecules in the construction of a 3D chain structure for cocrystal 1. Cocrystal 2, however, formed a zigzag 3D chain where the adjacent 4,4′-bipyridyl molecules are involved in a J-stacking mode. Experimental conductivity measurements of the cocrystals 1 and 2 with a Keithley 4200 SCS parameter analyzer showed the temperature-dependent semiconducting behavior in the case of cocrystal 1, whereas cocrystal 2 remained as an insulator. The favorable H-stacking interaction of 4,4′-bipyridine molecules which is the prime origin of semiconductivity in cocrystal 1 may become out of phase due to the free rotation along the C–C bond of 4,4′-bipyridine with an increase in temperature. Although the semiconducting behavior of a material increases with increasing temperature and decreases in resistivity, in the case of cocrystal 1 due to the probable phase transition of the 4,4′-bipyridyl molecules the material became an insulator with an increase in temperature from 20 °C to higher temperature, whereas the semiconducting behavior was restored after cooling the crystals to 20 °C again. The theoretical study conducted with the optimized structures of 1 and 2 showed the higher electron hopping rate in the case of cocrystal 1 as compared to 2 which can account for the charge conduction in the case of 1.

To achieve new breakthroughs in the development of synergistic antiviral medication cocrystals of acyclovir (AYL) with phenolic acids, a cocrystallization-driven strategy for optimizing the physicochemical properties and increasing the antiviral efficacy is proposed. This method emphasizes the structural features and medicinal value together with the dominant properties of gallic acid (GLA) to promote both solubility and permeability of AYL by cocrystallizing GLA into AYL’s lattice; meanwhile, the antiviral ability of ALY can be greatly increased by activating the antiviral potential of GLA and utilizing the synergistic antiviral activity of both in cocrystal formation. Guided by this idea, the first AYL-phenolic acid cocrystal, AYL-GLA-2H2O, is orientationally constructed and fully characterized. The accurate cocrystal structure revealed by single-crystal X-ray diffraction indicates that the entry of GLA into the AYL lattice has disrupted the homodimer of AYL itself, leading to the formation of a hydrophobic heterodimer between AYL and GLA molecules, coupled with an aqueous tetramer, thus endowing the cocrystal with both hydrophilic and hydrophobic characteristics. Such structural feature induces a concurrent enhancement in dissolubility and permeability of the cocrystal compared with the parent medicine. These observations can be strongly supported by density functional theory-based theoretical investigations involving molecular electrostatic potential, Hirshfeld surface, frontier molecular orbital, and Gibbs solvation free energy. Interestingly, the perfected AYL’s properties along with the stimulated antiviral activity of GLA enable the two ingredients in the cocrystal to display synergistic antiviral activity against the herpes simplex virus with a cooperativity index of less than 1, contributing to enhancing the antiviral ability. Thus, this contribution not only highlights the effectiveness of combining theory with experiment to solve AYL’s issues via the cocrystallization-driven method but fills in the gaps from previous studies on AYL-phenolic acid cocrystals with synergistic antiviral effects.

Quercetin, a naturally occurring bioflavonoid substance widely used in the nutraceutical and food industries, exists in various solid forms that can have different physicochemical properties, thus impacting this compound’s performance in various applications. In this work, we will clarify the complex solid-form landscape of this molecule. Two elusive isostructural solvates of quercetin were obtained from ethanol and methanol. The obtained crystals were characterized experimentally, but the crystallographic structure could not be solved due to their high instability. Nevertheless, the desolvated structure resulting from a high-temperature treatment (or prolonged storage at ambient conditions) of both these two labile crystals was characterized and solved via powder X-ray diffraction and solid-state nuclear magnetic resonance (SSNMR). This anhydrous crystal structure was compared with another anhydrous quercetin form obtained in our previous work, indicating that, at least, two different anhydrous polymorphs of quercetin exist. Navigating the solid-form landscape of quercetin is essential to ensure accurate control of the functional properties of food, nutraceutical, or pharmaceutical products containing crystal forms of this substance.

Photocyclization reactions are a useful tool for modulating the properties of metal–organic frameworks (MOFs). Fully characterizing these structural transitions is an important step in the development and deployment of MOF-based photoactive devices and smart materials. At present the quantitative measurement and modeling of photocyclization reactions in MOF materials has received relatively limited attention. In this work two different solid-state kinetic models are used to charactrerize a thermally reversible [2 + 2] photocyclization in [Cd2(bpdc)2(Py2TTF)2] (bpdc = biphenyl-4,4′-dicarboxylic acid Py2TTF = 2,6-bis(4′-pyridyl)-tetrathiafulvalene). Significant differences in the goodness-of-fit dependent on the reaction rate were observed between the two models, with the Finke–Watzky model providing a more accurate fit for the data.

Interactions between molecular modifiers and crystal surfaces govern numerous processes and structural outcomes of natural, biological, and synthetic crystallization. An efficient method of tailoring modifier–crystal interactions involves the design of imposters with structures and chemical functionalities that closely match those of the solute with subtle changes that preserve molecular recognition for modifier binding to crystal surfaces. Modifiers can function as inhibitors, promoters, or combinations of both to alter processes of crystal nucleation and growth. Here, we examine molecular modifiers that perturb the crystallization of ammonium urate (NH4HU), a pathological component of kidney stones, and a model system for assessing modifier–crystal interactions. Bulk crystallization assays were used to identify effective inhibitors and promoters of NH4HU crystallization. Two potent inhibitors, methyluric acid (MA) and poly(ethyleneimine) (PEIM), were identified where PEIM completely suppresses crystal growth at concentrations above 1.0 μg/mL, and MA displays a maximum growth inhibition of 60%. Time-resolved studies using a combination of microfluidics and atomic force microscopy elucidated the mechanisms by which each modifier influences layer generation and spreading on crystal surfaces. We used these techniques for select modifiers to quantify their effects on the anisotropic rates of crystallization and concomitant impact on crystal size and morphology. In situ characterization revealed that subtle changes in modifier functionality determine whether these imposters operate by either step pinning or kink blocking mechanisms. We demonstrated that molecular imposters of NH4HU crystallization operate by multiple, and sometimes opposing, roles of promotion and inhibition depending on the judicious selection of growth conditions. Collectively, our findings uncover trends among molecular imposters that are unique in relation to previously reported cases of crystal growth modification.

This study presents the development of novel supramolecular structures based on custom-designed porphyrin linker Zn(II)-5,10,15,20-tetra(4-bromo-2,6-difluoro phenyl) porphyrin (Zn–BFP). The porphyrin skeleton was specifically designed to introduce electron-withdrawing fluorine atoms near bromine atoms. The inclusion of fluorine atoms at 2,6-positions increases the polarizability of bromine atoms to participate more actively in halogen bonding interactions. The porphyrin Zn–BFP was synthesized by Adler’s method and fully characterized by 1H NMR. The absorbance, emission, and electrochemical studies of Zn–BFP were conducted to reveal the influence of fluorine substituents on the optical and electrochemical properties. Three new supramolecular solids [Zn(BFP)(H2O)]·acetone (1), [Zn(BFP)(NA)]·2DCM (2), and [Zn(BFP)(5-Br-NA)2] (3) in crystalline forms were synthesized by employing Zn–BFP with axial linkers nicotinic acid and 5-bromonicotinic acid. The axial linkers provided additional interaction sites in the form of COOH groups to involve in hydrogen bonding. Detailed single-crystal X-ray diffraction analyses revealed the existence of diverse halogen bonding contacts Br···Br, Br···O, and Br···π and hydrogen bonding motifs O–H···O between the metalloporphyrin units leading to 1D chains and 2D supramolecular sheets. The findings of particular interest are the existence of relatively shortest Br···Br interactions in compound 2. Hirshfeld surface analyses revealed the contributions of various interactions toward the stability of the extended architectures. Morphological studies supported distinct supramolecular features exhibited by the fluorine-appended porphyrins. Electrostatic potential isosurfaces with the aid of density functional theory indicated that fluorine atom substitution at the 2,6-positions of the bromo phenyl moiety enhances the σ-hole potential by 5.2 kcal/mol, clearly suggesting the expansion of the σ-hole.

The influence of the solution environment on the solution thermodynamics, crystallizability, and nucleation of tolfenamic acid (TFA) in five different solvents (isopropanol, ethanol, methanol, toluene, and acetonitrile) is examined using an integrated workflow encompassing both experimental studies and intermolecular modeling. The solubility of TFA in isopropanol is found to be the highest, consistent with the strongest solvent–solute interactions, and a concomitantly higher than ideal solubility. The crystallizability is found to be highly dependent on the solvent type with the overall order being isopropanol < ethanol < methanol < toluene < acetonitrile with the widest solution metastable zone width in isopropanol (24.49 to 47.41 °C) and the narrowest in acetonitrile (8.23 to 16.17 °C). Nucleation is found to occur via progressive mechanism in all the solvents studied. The calculated nucleation parameters reveal a considerably higher interfacial tension and larger critical nucleus radius in the isopropanol solutions, indicating the higher energy barrier hindering nucleation and hence lowering the nucleation rate. This is supported by diffusion coefficient measurements which are lowest in isopropanol, highlighting the lower molecular diffusion in the bulk of solution compared to the other solutions. The TFA concentration and critical supersaturation at the crystallization onset is found to be directly correlated with TFA/isopropanol solutions having the highest values of solubility and critical supersaturation. Intermolecular modeling of solute–solvent interactions supports the experimental observations of the solubility and crystallizability, highlighting the importance of understanding solvent selection and solution state structure at the molecular level in directing the solubility, solute mass transfer, crystallizability, and nucleation kinetics.

The synthesis and experimental testing of energetic materials can be hazardous, but their many industrial and military applications necessitate their constant research and development. We evaluate computational methods for predicting the crystal structures of energetic molecular organic crystals from their molecular structure as a first step in computationally evaluating materials, which could guide experimental work. Crystal structure prediction (CSP) is evaluated on a test set of 10 energetic materials with known crystal structures, initially using a rigid-molecule, anisotropic atom–atom force-field approach, followed by reoptimization of predicted crystal structures using dispersion-corrected solid-state density functional theory (DFT). CSP using the force field was found to provide good results for some molecules, whose known crystal structures are reproduced by one of the lowest-energy predictions, but are more variable than typical results for other small organic molecules. Reoptimization of predicted crystal structures using solid-state DFT leads to reliable predictions, demonstrating CSP as an approach that can be applied in the area of energetic materials discovery and development.