Evaluating structure-property relationship in a new family of mechanically flexible co-crystals.

A structure-property analysis of ten compositionally and chemically similar co-crystals of -(pyridin-2-yl)alkylamides and carboxylic acids shows that three co-crystals of targets bearing a methyl chain were brittle, while the remaining co-crystals of targets bearing ethyl or propyl chains were flexible. Five of these displayed elastic deformation while two displayed plastic deformation. Compounds with different mechanical behaviour (brittle, plastic, and elastic deformation) in response to external mechanical stimuli could be organized into structurally similar groups based on the presence of specific intermolecular interactions and packing features in each crystal structure.

The Balance between Hydrogen Bonds, Halogen Bonds, and Chalcogen Bonds in the Crystal Structures of a Series of 1,3,4-Chalcogenadiazoles.

In order to explore how specific atom-to-atom replacements change the electrostatic potentials on 1,3,4-chalcogenadiazole derivatives, and to deliberately alter the balance between intermolecular interactions, four target molecules were synthesized and characterized. DFT calculations indicated that the atom-to-atom substitution of Br with I, and S with Se enhanced the σ-hole potentials, thus increasing the structure directing ability of halogen bonds and chalcogen bonds as compared to intermolecular hydrogen bonding. The delicate balance between these intermolecular forces was further underlined by the formation of two polymorphs of 5-(4-iodophenyl)-1,3,4-thiadiazol-2-amine; Form I displayed all three interactions while Form II only showed hydrogen and chalcogen bonding.

Establishing Halogen-Bond Preferences in Molecules with Multiple Acceptor Sites.

The interplay between hydrogen bonds (HBs) and halogen bonds (XBs), has been addressed by co-crystallizing two halogen bond donors, 1,4-diiodotetrafluorbenzene(DITFB) and 1,3,5-trifluoro-2,4,6-triiodobenzene(TITFB) with four series of targets; N-(pyridin-2-yl)benzamide (Bz-X), N-(pyridin-2-yl)picolinamides (2Pyr-X), N-(pyridin-2-yl)nicotinamides (3Pyr-X), N-(pyridin-2-yl)isonicotinamides (4Pyr-X); X=H/Cl/Br/I. The structural outcomes were compared with interactions in the targets themselves. 13 co-crystals were analysed by single-crystal X-ray diffraction (SCXRD).

The Impact of Halogen Substituents on the Synthesis and Structure of Co-Crystals of Pyridine Amides.

Strategies for co-crystal synthesis tend to employ either hydrogen- or halogen-bonds between different molecules. However, when both interactions are present, the structural influence that they may exert on the resulting assembly is difficult to predict a priori. To shed some light on this supramolecular challenge, we attempted to co-crystallize ten aliphatic dicarboxylic acids (co-formers) with three groups of target molecules; -(pyridin-2-yl)picolinamides (2Pyr-), -(pyridin-2-yl)nicotinamides (3Pyr-), -(pyridin-2-yl)isonicotinamides (4Pyr-); X=Cl/ Br/ I.

Modulating the physical properties of solid forms of urea using co-crystallization technology.

The solid-form landscape of urea was explored using full interaction maps (FIMs) and data from the CSD to develop optimum protocols for synthesizing co-crystals of urea. As a result, 49 of the 60 attempted reactions produced new co-crystals, and the crystal structures of four of these are presented. Moreover, the goal of reducing the solubility and lowering the hygroscopicity of the parent compound was achieved, which in turn offers new opportunities for application as a slow-release fertilizer with limited hygroscopicity, thereby reducing many current problems of transport, handling, and storage of urea.

Structural Examination of Halogen-Bonded Co-Crystals of Tritopic Acceptors.

A series of tritopic -heterocyclic compounds containing electrostatically and geometrically equivalent binding sites were synthesized and subjected to systematic co-crystallizations with selected perfluoroiodoarenes in order to map out their structural landscapes. More than 70% of the attempted reactions produced a co-crystal as indicated by IR spectroscopy. Four new crystal structures are reported and in all of them, at least one potential binding site on the acceptor is left vacant.

Enantioselective copper catalysed C-H insertion reaction of 2-sulfonyl-2-diazoacetamides to form γ-lactams.

The first examples of asymmetric copper-catalysed intramolecular C-H insertion reactions of 2-sulfonyl-2-diazoacetamides are described; trans γ-lactams with up to 82% ee are achieved with the CuCl2-bisoxazoline-NaBARF catalyst system. The reactions generally display high efficiency and high trans selectivity, and also a strong regiochemical preference for insertion to lead to the formation of 5-membered rings over 4-membered rings. In cases where there are competing C-H insertion pathways available, to form sulfolanes or thiopyrans, only the insertion into the amide chain to form γ-lactams is observed.

A versatile and green mechanochemical route for aldehyde-oxime conversions.

A robust, facile and solvent-free mechanochemical path for aldehyde-oxime transformations using hydroxylamine and NaOH is explored; the method is suitable for aromatic and aliphatic aldehydes decorated with a range of substituents.

Halogen bonding or close packing? Examining the structural landscape in a series of Cu(II)-acac complexes.

A series of four bifunctional ligands based on β-diketonate moieties bearing methyl (2), chloro (3), bromo (4) and iodo (5) substituents and their corresponding Cu(II) complexes have been synthesized and crystallographically characterized in order to explore the possibility of using halogen bonds for the directed assembly of predictable architectures in coordination chemistry. The four ligands have characteristic O-H···O intramolecular hydrogen bonds and the structure of ligand 2 is close packed whereas, ligands 3, 4 and 5 contain extended 1-D architectures based on C=O···X halogen bonds. In each case, the halogen-bond donor seeks out the most powerful halogen-bond acceptor (based on electrostatic considerations).