Green and Scalable Preparation of Highly Conductive Alkali Metal-dhta Coordination Polymers.

2,5-Dihydroxyterephthalic acid (H) is well-known for its use in the construction of functional metal-organic frameworks (MOFs). Among them, simple coordination polymers (CPs), such as lithium and sodium coordination polymers with H, have been used successfully to synthesize electrically conductive MOFs and have also demonstrated great potential as positive or negative electrode materials on their own. However, there has been little exploration of the structure and physicochemical properties of these and other alkali complexes of H.

The seventh blind test highlights exciting developments in crystal structure prediction.

Two reports on the seventh blind test on crystal structure prediction extensively discuss the cutting-edge avant-garde methods of structure generation and energy ranking.

Perhalogenated Anilines as Bifunctional Donors of Hydrogen and Halogen Bonds in Cocrystals with Ditopic Nitrogen-Containing Acceptors.

In this study, we examine the experimental and theoretical capabilities of two perhalogenated anilines, 2,3,5,6-tetrafluoro-4-bromoaniline () and 2,3,5,6-tetrafluoro-4-iodoaniline () as hydrogen and halogen bond donors. A series of 11 cocrystals derived from the two anilines and selected ditopic nitrogen-containing acceptors (4,4'-bipyridine, 1,2-bis(4-pyridyl)ethane, and 1,4-diazabicyclo[2.2.

Influence of N-protonation on electronic properties of acridine derivatives by quantum crystallography.

Applications of 9-aminoacridine (9aa) and its derivatives span fields such as chemistry, biology, and medicine, including anticancer and antimicrobial activities. Protonation of such molecules can alter their bioavailability as weakly basic drugs like aminoacridines exhibit reduced solubility at high pH levels potentially limiting their effectiveness in patients with elevated gastric pH. In this study, we analyse the influence of protonation on the electronic characteristics of the molecular organic crystals of 9-aminoacridine.

Halogen bonding with carbon: directional assembly of non-derivatised aromatic carbon systems into robust supramolecular ladder architectures.

Carbon, although the central element in organic chemistry, has been traditionally neglected as a target for directional supramolecular interactions. The design of supramolecular structures involving carbon-rich molecules, such as arene hydrocarbons, has been limited almost exclusively to non-directional π-stacking, or derivatisation with heteroatoms to introduce molecular assembly recognition sites. As a result, the predictable assembly of non-derivatised, carbon-only π-systems using directional non-covalent interactions remains an unsolved fundamental challenge of solid-state supramolecular chemistry.

Illuminating milling mechanochemistry by tandem real-time fluorescence emission and Raman spectroscopy monitoring.

In pursuit of accessible and interpretable methods for direct and real-time observation of mechanochemical reactions, we demonstrate a tandem spectroscopic method for monitoring of ball-milling transformations combining fluorescence emission and Raman spectroscopy, accompanied by high-level molecular and periodic density-functional theory (DFT) calculations, including periodic time-dependent (TD-DFT) modelling of solid-state fluorescence spectra. This proof-of-principle report presents this readily accessible dual-spectroscopy technique as capable of observing changes to the supramolecular structure of the model pharmaceutical system indometacin during mechanochemical polymorph transformation and cocrystallisation. The observed time-resolved spectroscopic and kinetic data are supported by X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements.

Three-in-One: Dye-Volatile Cocrystals Exhibiting Intensity-Dependent Photochromic, Photomechanical, and Photocarving Response.

Cocrystallization of a -azobenzene dye with volatile molecules, such as pyrazine and dioxane, leads to materials that exhibit at least three different light-intensity-dependent responses upon irradiation with low-power visible light. The halogen-bond-driven assembly of the dye -(-iodoperfluorophenyl)azobenzene with volatile halogen bond acceptors produces cocrystals whose light-induced behavior varies significantly depending on the intensity of the light applied. Low-intensity (<1 mW·cm) light irradiation leads to a color change associated with low levels of → isomerization.

Elucidating mechanochemical reactivity of a ternary halogen-bonded cocrystal system by computational and calorimetric studies.

Discovery of a halogen-bonded ternary cocrystal of 1,3,5-trifluoro-2,4,6-triiodobenzene with pyrazine and triphenylphosphine sulfide has revealed a complex landscape of multicomponent phases, all achievable by mechanochemical interconversion. The observed solid-state reaction pathways were explained by periodic density-functional calculations and comprehensive intermolecular interaction analysis, supported by dissolution calorimetry measurements.

Experimental and Theoretical Evaluation of the Thermodynamics of the Carbonation Reaction of ZIF-8 and Its Close-Packed Polymorph with Carbon Dioxide.

We report the first experimental and theoretical evaluation of the thermodynamic driving force for the reaction of metal-organic framework (MOF) materials with carbon dioxide, leading to a metal-organic carbonate phase. Carbonation upon exposure of MOFs to CO is a significant concern for the design and deployment of such materials in carbon storage technologies, and this work shows that the formation of a carbonate material from the popular SOD-topology framework material ZIF-8, as well as its dense-packed -topology polymorph, is significantly exothermic. With knowledge of the crystal structure of the starting and final phases in the carbonation reaction, we have also identified periodic density functional theory approaches that most closely reproduce the measured reaction enthalpies.

Hirshfeld atom refinement of metal-organic frameworks for accurate positioning of hydrogen atoms and disorder analysis.

The application of Hirshfeld atom refinement (HAR) fragmentation is demonstrated for the refinement of metal-organic framework (MOF) crystal structures. The presented method enables anisotropic refinement of imidazolate hydrogen atoms, as well as complex analysis of solvent disorder within MOF pores. The data used were derived from standard resolution in-house single crystal X-ray diffraction measurements, demonstrating that high quality structural analysis of MOFs no longer requires access to neutron or synchrotron facilities.

Computational evaluation of halogen-bonded cocrystals enables prediction of their mechanochemical interconversion reactions.

Periodic density-functional theory (DFT) calculations were used to predict the thermodynamic stability and the likelihood of interconversion between a series of halogen-bonded cocrystals. The outcomes of mechanochemical transformations were in excellent agreement with the theoretical predictions, demonstrating the power of periodic DFT as a method for designing solid-state mechanochemical reactions prior to experimental work. Furthermore, the calculated DFT energies were compared with experimental dissolution calorimetry measurements, marking the first such benchmark for the accuracy of periodic DFT calculations in modelling transformations of halogen-bonded molecular crystals.

Experimentally Validated Ab Initio Crystal Structure Prediction of Novel Metal-Organic Framework Materials.

First-principles crystal structure prediction (CSP) is the most powerful approach for materials discovery, enabling the prediction and evaluation of properties of new solid phases based only on a diagram of their underlying components. Here, we present the first CSP-based discovery of metal-organic frameworks (MOFs), offering a broader alternative to conventional techniques, which rely on geometry, intuition, and experimental screening. Phase landscapes were calculated for three systems involving flexible Cu(II) nodes, which could adopt a potentially limitless number of network topologies and are not amenable to conventional MOF design.

Low-Dimensional Magnetism in Multivariate Copper/Zinc MOF-74 Materials Formed via Different Mechanochemical Methods.

MOF-74 is an archetypal magnetic metal-organic framework (MOF) family, with metal nodes bridged by 2,5-dioxido-1,4-benzenedicarboxylic acid (Hdobdc) and arranged into one of the simplest representations of the 1D Ising magnetic model. Recently, a novel mechano-synthetic approach opened a pathway toward a series of bimetallic multivariate (1:1) M1M2-MOF-74 materials, with the uniform distribution of metal cations in the oxometallic chains, offering a unique opportunity to investigate low-dimensional magnetism in these heterometallic MOFs. We explore here how different mechanochemical procedures affect the interaction between the metal nodes of the model system of three multivariate copper(II)/zinc(II)-MOF-74 materials, two of which were obtained through a template-controlled procedure, and the third one was obtained by recently developed mechanical MOF-alloying combined with subsequent accelerated aging.

Polymorphs and solid solutions: materials with new luminescent properties obtained through mechanochemical transformation of dicyanoaurate(I) salts.

We report the use of mechano- and thermochemical methods to create new solid-state luminescent materials from well-known inorganic salts, potassium dicyanoaurate(I) KAu(CN), and potassium dicyanocuprate(I) KCu(CN). In particular, manual grinding or ball milling of commercial samples of KAu(CN) led to the formation of a novel polymorph of the salt, herein termed -KAu(CN), evident by a significant change in color of the fluorescence emission of the solid material from orange to violet. The formation of -KAu(CN) is reversible upon addition of small amounts of solvents, and powder X-ray diffraction analysis indicates that the structure of -KAu(CN) might be related to that of pristine KAu(CN) through a change in ordering of Au(CN) ions in a layered structure.

Effect of Vehicle Composition on the Preparation of Different Types of Dapsone Crystals for Topical Drug Delivery.

Topical formulations composed of API-pure crystals have been increasingly studied, especially in regards to the impact of particle size in penetration efficiency. Less attention, however, has been devoted to the solid-state properties of drugs delivered to the skin. In this study, we address the effect of formulation composition on the crystal form existing in topical products.

Metal-organic frameworks as hypergolic additives for hybrid rockets.

Hybrid rocket propulsion can contribute to reduce launch costs by simplifying engine design and operation. Hypergolic propellants, igniting spontaneously and immediately upon contact between fuel and oxidizer, further simplify system integration by removing the need for an ignition system. Such hybrid engines could also replace currently popular hypergolic propulsion approaches based on extremely toxic and carcinogenic hydrazines.

Mechanochemical Synthesis of Polymorphic Urea ⋅ Adipic Acid Cocrystal as a Sustained-Release Nitrogen Source.

A 2 : 1 urea ⋅ adipic acid cocrystal was obtained in two polymorphic forms (Form I reported earlier, and Form II synthesized in this study) using mechanochemistry as well as solution crystallization. Lower solubility and leaching study showed the newly synthesized urea ⋅ adipic acid 2 : 1 cocrystal to be an efficient sustained-release nitrogen fertilizer compared to commercially available urea.

Simplifying and expanding the scope of boron imidazolate framework (BIF) synthesis using mechanochemistry.

Mechanochemistry enables rapid access to boron imidazolate frameworks (BIFs), including ultralight materials based on Li and Cu(i) nodes, as well as new, previously unexplored systems based on Ag(i) nodes. Compared to solution methods, mechanochemistry is faster, provides materials with improved porosity, and replaces harsh reactants (-butylithium) with simpler and safer oxides, carbonates or hydroxides. Periodic density-functional theory (DFT) calculations on polymorphic pairs of BIFs based on Li, Cu and Ag nodes reveals that heavy-atom nodes increase the stability of the open SOD-framework relative to the non-porous dia-polymorph.

Mechanochemical Synthesis and Physicochemical Characterization of Previously Unreported Praziquantel Solvates with 2-Pyrrolidone and Acetic Acid.

Two new solvates of the widely used anthelminthic Praziquantel (PZQ) were obtained through mechanochemical screening with different liquid additives. Specifically, 2-pyrrolidone and acetic acid gave solvates with 1:1 stoichiometry (PZQ-AA and PZQ-2P, respectively). A wide-ranging characterization of the new solid forms was carried out by means of powder X-ray diffraction, differential scanning calorimetry, FT-IR, solid-state NMR and biopharmaceutical analyses (solubility and intrinsic dissolution studies).

Real-Time Observation of "Soft" Magic-Size Clusters during Hydrolysis of the Model Metallodrug Bismuth Disalicylate.

Colloidal bismuth therapeutics have been used for hundreds of years, yet remain mysterious. Here we report an X-ray pair distribution function (PDF) study of the solvolysis of bismuth disalicylate, a model for the metallodrug bismuth subsalicylate (Pepto-Bismol). This reveals catalysis by traces of water, followed by multistep cluster growth.

Mechanochemical reactivity inhibited, prohibited and reversed by liquid additives: examples from crystal-form screens.

We demonstrate that liquid additives can exert inhibitive or prohibitive effects on the mechanochemical formation of multi-component molecular crystals, and report that certain additives unexpectedly prompt the dismantling of such solids into physical mixtures of their constituents. Computational methods were employed in an attempt to identify possible reasons for these previously unrecognised effects of liquid additives on mechanochemical transformations.

Challenging the Ostwald rule of stages in mechanochemical cocrystallisation.

Mechanochemistry provides an efficient, but still poorly understood route to synthesize and screen for polymorphs of organic solids. We present a hitherto unexplored effect of the milling assembly on the polymorphic outcome of mechanochemical cocrystallisation, tentatively related to the efficiency of mechanical energy transfer to the milled sample. Previous work on mechanochemical cocrystallisation has established that introducing liquid or polymer additives to milling systems can be used to direct polymorphic behavior, leading to extensive studies how the amount and nature of grinding additive affect reaction outcome and polymorphism.

Linker Substituents Control the Thermodynamic Stability in Metal-Organic Frameworks.

We report the first systematic experimental and theoretical study of the relationship between the linker functionalization and the thermodynamic stability of metal-organic frameworks (MOFs) using a model set of eight isostructural zeolitic imidazolate frameworks (ZIFs) based on 2-substituted imidazolate linkers. The frameworks exhibit a significant (30 kJ·mol) variation in the enthalpy of formation depending on the choice of substituent, which is accompanied by only a small change in molar volume. These energetics were readily reproduced by density functional theory (DFT) calculations.

Mechanochemical reactions of cocrystals: comparing theory with experiment in the making and breaking of halogen bonds in the solid state.

Mechanochemical re-investigation of the halogen-bonded cocrystallisation of 1,4-diazabicyclo[2.2.2]-octane and 1,2-diiodotetrafluorobenzene revealed an unexpectedly complex system with three distinct cocrystal compositions, one of which also exhibits temperature-dependent polymorphism.