Discovery of a polymorph of tris(p-tolyl)antimony(III) reveals solid-state supramolecular dimers connected through short, attractive Sb∙∙∙Sb contacts that, based on theoretical calculations and a systematic screen of the Cambridge Structural Database (CSD), could be an overlooked hallmark of the solid-state and supramolecular chemistry of trivalent organoantimony(III) compounds. While the previously reported crystal structure of tris(p-tolyl)antimony(III) is known to exhibit phenyl embrace motifs, resembling the arsenic or phosphorus analogs, the new polymorph exhibits supramolecular dimers characterized by direct Sb∙∙∙Sb contacts shorter than the sum of the van der Waals radii, and stabilized by a significant dimer dissociation energy of ca. -26 kJ mol-1 established by periodic density-functional calculations. Theoretical analysis indicates that the contacts are attractive and dispersion-dominated, with an overview of the CSD showing that such direct Sb···Sb contacts are not unique to this polymorphic form of tris(p-tolyl)antimony(III) but appear to be a more general feature of trivalent organoantimony in the solid state. Specifically, the CSD shows that dimers based on short Sb···Sb contacts are found across a number of organoantimony structures, including some of the simplest representatives of the series, such as triphenyl- and trimethylantimony, for which the dimer interaction energy is herein calculated to be ca. -13 kJ mol-1.

Low-frequency Raman, also known as terahertz-Raman (THz-Raman), spectroscopy offers a laboratory benchtop-based alternative to synchrotron X-ray diffraction for real-time, in situ monitoring of ball-milling mechanochemical reactions. Although direct monitoring of the long-range structure of materials during mechanochemical reactions is generally challenging by conventional Raman spectroscopy, and typically requires synchrotron X-ray diffraction, here we use THz-Raman spectroscopy to monitor mechanosynthesis of cocrystals, stoichiomorphs, and polymorphs, detect multi-step sequences, and discover solid-state phases in systems difficult to differentiate using fingerprint-region Raman spectroscopy—all through real-time observation of changes in lattice vibrational models. The methodology is augmented by periodic density functional theory (DFT), which enables structural interpretation of spectroscopic changes, notably the identification of THz-Raman bands associated with halogen bond transformations. Simultaneous monitoring of mechanochemical processes in both the fingerprint and low-frequency Raman regions enables real-time observation of changes to extended as well as molecular structure during milling, in a single laboratory benchtop experiment, without synchrotron radiation.

Cocrystallization of a cis-azobenzene dye with volatile cocrystal former molecules, such as pyrazine and dioxane, leads to materials that exhibit at least three different light intensity-dependent responses upon irradiation with low-energy visible light. Specifically, the halogen bond-driven assembly of cis-(p-iodoperfluorophenyl)azobenzene with volatile halogen bond acceptors produces cocrystals whose light-induced behaviour varies significantly depending on the intensity of the light applied. Low-intensity (<1 mW∙cm-2) light irradiation leads to a colour change due to low levels of cis-trans isomerization. Irradiation at higher intensities (150 mW∙mm-2) produces photo-mechanical bending, caused by more extensive azo dye isomerization. At still higher irradiation intensities (2.25 W∙mm-2) the cocrystals undergo photo-carving, i.e. they are readily shaped, punctured, and cut with micrometer precision using laser light. This work demonstrates how the recently reported photo-carving behaviour can be combined with different types of photo-responses, providing a design for multi-responsive materials that can respond to different levels of irradiation with optical colour change, photo-mechanical bending, or photo-carving, as laser power is increased.

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.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Enantioenriched heterocyclic and rigidified bioisosteres of amino acids are valuable building blocks in drug discovery, particularly in the design of peptidomimetic drugs. The rigidified bioisostere of phenylalanine, 1,2,3,4-tetrahydroquinoline-2-carboxylic acid, is found in a number of biologically active compounds. However, only a small number of successful methodologies have been reported for its asymmetric synthesis. In an effort to develop an environmentally benign and metal-free organocatalytic process for the preparation of this compound, a number of novel P-chiral, N-phosphoryl sulfonamide Brønsted acids were synthesized and evaluated in a biomimetic transfer hydrogenation reaction of quinoline-2-carboxylates to give the (R)-1,2,3,4-tetrahydroquinoline-2-carboxylates.

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. Here, we propose and validate a different paradigm for the reliable assembly of carbon-only aromatic systems into predictable supramolecular architectures: not through non-directional π-stacking, but via specific and directional halogen bonding. We present a systematic experimental, theoretical and database study of halogen bonds to carbon-only π-systems (C–I⋯πC bonds), focusing on the synthesis and structural analysis of cocrystals with diversely-sized and -shaped non-derivatised arenes, from one-ring (benzene) to 15-ring (dicoronylene) polycyclic atomatic hydrocarbons (PAHs), and fullerene C60, along with theoretical calculations and a systematic analysis of the Cambridge Structural Database. This study establishes C–I⋯πC bonds as directional interactions to arrange planar and curved carbon-only aromatic systems into predictable supramolecular motifs. In >90% of herein presented structures, the C–I⋯πC bonds to PAHs lead to a general ladder motif, in which the arenes act as the rungs and halogen bond donors as the rails, establishing a unique example of a supramolecular synthon based on carbon-only molecules. Besides fundamental importance in the solid-state and supramolecular chemistry of arenes, this synthon enables access to materials with exciting properties based on simple, non-derivatised aromatic systems, as seen from large red and blue shifts in solid-state luminescence and room-temperature phosphorescence upon cocrystallisation.

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)2, and potassium dicyanocuprate(I) KCu(CN)2. In particular, manual grinding or ball milling of commercial samples of KAu(CN)2 led to the formation of a novel polymorph of the salt, herein termed m-KAu(CN)2, evident by a significant change in color of the fluorescence emission of the solid material from orange to violet. The formation of m-KAu(CN)2 is reversible upon addition of small amounts of solvents, and powder X-ray diffraction analysis indicates that the structure of m-KAu(CN)2 might be related to that of pristine KAu(CN)2 through a change in ordering of Au(CN)2- ions in a layered structure. Thermal treatment of KAu(CN)2 led to the discovery of another polymorph of this well-known salt, herein termed t-KAu(CN)2, making KAu(CN)2 a rare example of a system in which thermochemical and mechanochemical treatments lead to the formation of different, in each case previously not reported, polymorphic forms. The thermally-induced transformation from KAu(CN)2 to t-KAu(CN)2 takes place around 250 °C and proceeds in a crystal-to-crystal fashion, which enabled the preliminary structural characterisation through single crystal X-ray diffraction, revealing the retention of the layered structure and a change in ordering of Au(CN)2- ions. Milling of the simple salt KAu(CN)2 in the presence of equimolar amounts or less of its copper(I)-based analogue coordination polymer KCu(CN)2 leads to the formation of a series of solid solution materials, isostructural to m-KAu(CN)2 and with visible fluorescence emission distinct from KCu(CN)2 or any herein investigated forms of KAu(CN)2.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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 arenes, has almost exclusively been limited to π-stacking of aromatic systems, or derivatization with heteroatoms as sites for molecular recognition. Here, we demonstrate that C-I···Cπ halogen bonds to carbon-based π-systems can be reliably used as direction-al interactions for the creation of extended structures based on planar, as well as curved aromatic systems, without any need for derivatization or π-stacking. Specifically, we describe the first systematic study of a series of cocrystals containing non-derivatized carbon-only aromatic systems of different sizes and shapes, including polycyclic aromatic hydrocarbons (PAHs) and fullerene C60, which are held together by directional halogen bonds to aromatic carbon atoms. In a large majority (~90%) of structures, the C-I···Cπ halogen bonding with PAHs leads to a supramolecular ladder-like motif, in which the PAHs act as the rungs and halogen bond donors as rails, demonstrating this motif as the first example of a supramolecular synthon based on carbon. These results, supported by novel cocrystal structures, theoretical calculations, and a systematic analysis of the Cambridge Structural Database, offer a new, previously overlooked paradigm for the assembly of carbon-only aromatic systems, not based on π-stacking, but via specific, directional halogen bonding. This new ability to use a car-bon-based supramolecular synthon to direct the assembly aromatic systems provides an exciting opportunity to create materials with new and modified properties based on non-derivatized aromatic systems, as seen from large red and blue shifts in solid-state luminescence for cocrystals of pyrene, coronene and perylene, as well as the appearance of room-temperature phosphorescence upon cocrystal formation.

The formation of co-crystals by the assembly of molecules with complementary molecular recognition functionalities is a popular strategy to design or improve a range of solid-state properties, including those relevant for pharmaceuticals, photo- or thermoresponsive materials and organic electronics. Here, we report halogen-bonded co-crystals of a fluorinated azobenzene derivative with a volatile component—either dioxane or pyrazine—that can be cut, carved or engraved with low-power visible light. This cold photo-carving process is enabled by the co-crystallization of a light-absorbing azo dye with a volatile component, which gives rise to materials that can be selectively disassembled with micrometre precision using low-power, non-burning laser irradiation or a commercial confocal microscope. The ability to shape co-crystals in three dimensions using laser powers of 0.5–20 mW—substantially lower than those used for metals, ceramics or polymers—is rationalized by photo-carving that targets the disruption of weak supramolecular interactions, rather than the covalent bonds or ionic structures targeted by conventional laser beam or focused ion beam machining processes.

Cocrystallisation of a fluorinated azobenzene with volatile cocrystal components dioxane or pyrazine yields halogen-bonded cocrystals that can be cut, carved or engraved with low-powered visible laser light. This process, termed cocrystal laser micro-shaping (CLMS), is enabled by cocrystallisation of a visible light dye with a volatile component, giving rise to materials that can be selectively disassembled with micrometer precision using gentle, non-burning irradiation in a commercial confocal microscope setup. The ability to shape and even machine cocrystals in 3D using laser powers between 0.5 and 20 mW, which are 2-4 orders of magnitude lower compared to laser powers used for machining metals, ceramics or polymers, is rationalized by CLMS targeting the disruption of weak supramolecular interactions between cocrystal components, rather than the breaking of covalent bonds in polymers or disruption of ionic structures required for conventional laser beam or focused ion beam machining processes, mainly by high-power laser heating.

We report the first X-ray single crystal structures of hypochlorite (ClO - ) and hypobromite (BrO - ) salts, including hydrated sodium hypochlorite - a staple of the chlorine industry and ubiquitous bleaching and disinfection agent for almost 200 years. The structures, supported by variable-temperature Raman spectroscopy on individual crystals and periodic density-functional theory (DFT) calculations, provide insight into solid-state geometry and supramolecular chemistry of hypohalite ions.

Unlike the closely related and widely investigated amidino-substituted benzimidazoles and benzothiazoles with a range of demonstrated biological activities, the matching benzoxazole analogues still remain a largely understudied and not systematically evaluated class of compounds. To address this challenge, we utilized the Pinner reaction to convert isomeric cyano-substituted 2-aminophenols into their amidine derivatives, which were isolated as hydrochlorides and/or zwitterions, and whose structure was confirmed by single crystal X-ray diffraction. The key step during the Pinner synthesis of the crucial carboximidate intermediates was characterized through mechanistic DFT calculations, with the obtained kinetic and thermodynamic parameters indicating full agreement with the experimental observations. The obtained amidines were subjected to a condensation reaction with aryl carboxylic acids that allowed the synthesis of a new library of 5- and 6-amidino substituted 2-arylbenzoxazoles. Their antiproliferative features against four human tumour cell lines (SW620, HepG2, CFPAC-1, HeLa) revealed sub-micromolar activities on SW620 for several cyclic amidino 2-naphthyl benzoxazoles, thus demonstrating the usefulness of the proposed synthetic strategy and promoting amidino substituted 2-aminophenols as important building blocks towards biologically active systems.

Strong intermolecular interactions serve as vital tools in cocrystal assembly.Halogen bonding (XB) [1], a highly directional interaction, is most often observed between a halogen-atom donor and electron-rich acceptors, such as oxygen or nitrogen.However, XBs can also be used for the organization of arenes in the solid state through interactions with aromatic -systems, as previously explored in the dichroic and pleochroic cocrystals of naphthalene or azulene, respectively.[2] This presentation will outline our study of XB cocrystal structures containing various polycyclic aromatic hydrocarbons (PAHs), and evaluate the reliability of halogen bonding to carbon as an overlooked tool for crystal engineering.

Laser beam machining (LBM) of ceramics, polymers, or metals is usually performed using high-power femtosecond lasers (4-20 W).Using LBM, micro-or nano-sized patterns can be machined into surfaces of these materials to alter their properties for various applications.A drawback of such high-power techniques is the possibility of considerable chemical damage to the surface of the machined materials.We now report the use of halogen bonding to generate new dye-based cocrystals with volatile cocrystal-forming molecules (coformers) that can be etched, cut, and punctured with micrometer-scale precision using low-powered laser beams (for example, between 0.5 and 20 mW).[1] This unique phenomenon, shown to be wavelength-tunable and powerdependent, can be utilized to machine molecular crystals by forming holes or cuts of controllable sizes.Using a microscope-guided low-power laser beam numerical control of this process can be achieved, enabling a variety of complex patterns to be inscribed onto the surface of molecular cocrystals.A mechanism is proposed with the volatile conformer acting as a leaving group, giving the ability to gently inscribe patterns using a low-power laser beam, without chemical decomposition of the cocrystals.This has not been previously reported in small molecule organic solids and appears to be a new emergent property achievable through crystal engineering by halogen bonding, opening a new type of materials to micrometer-scale shaping and machining applications.