From liquid to crystal via mechanochemical grinding: unique host-guest (HOF) cocrystal.

Mechanochemical synthesis via grinding of trimesic acid (TA, C9H6O6) and 4-chlorophenyl diphenyl phosphate (4CDP, C18H14ClO4P) (liquid at room temperature) in a 1:1 ratio resulted in the formation of an inclusion type of cocrystal. The crystallization of this phase via slow evaporation at low temperature (276-277 K) from methanol resulted in a rare `stairstep morphology' during the process of crystal growth. This morphology was not observed after crystallization of the compound from other solvents like toluene, dichloromethane, acetone, hexane and isooctane, and hence this was characteristically observed in methanol only. The characterization from single-crystal X-ray diffraction revealed the formation of a cocrystal with five molecules of TA and two molecules of 4CDP in the asymmetric unit. The trimesic acid molecules form hydrogen-bonded dimers resulting in hexagonal rings, and these rings are stacked through π-π intermolecular interactions to make a hexagonal honeycomb-like structure. The phosphate molecules, 4CDP, were found to be trapped as guests in these hexagonal channels. The similarity in the packing of trimesic acid is compared in the cocrystal and the free acid quantitatively via Xpac analysis, which establishes the relationship of a `2D supramolecular construct' between them. This signifies a unique type of arrangement in which the voids created by the trimesic acid moiety do not undergo distortion by the inclusion of the guest molecules. The quantitative analysis of the intermolecular interactions using Hirshfeld surfaces and fingerprint plots deciphers the role of both strong O-H...O hydrogen bonds and weak intermolecular interactions in the crystal packing.

Quantitative evaluation of the electronic features involving "nucleophilic-electrophilic" character in the chalcogen sulfur.

This study investigates the crystal structures of substituted thiophenes and isothiocyanates by utilizing the method of in situ cryo-crystallization to gain quantitative insights into the electronic features of sulfur-centered interactions. This work reveals that the role of sulfur as a "nucleophilic" or "electrophilic" species during non-covalent interaction is significantly influenced by its immediate chemical and electronic surroundings.

Plastic Deformation in a Molecular Crystal Enables a Piezoresistive Response.

Organic materials are promising candidates for the development of efficient sensors for many medicinal and materials science applications. Single crystals of a small molecule, 4-trifluoromethyl phenyl isothiocyanate (4CFNCS), exhibit plastic deformation when bent, twisted, or coiled. Synchrotron micro-focus X-ray diffraction mapping of the bent region of the crystal confirms the mechanism of deformation. The crystals are incorporated into a flexible piezoresistive sensor using a composite constituting PEDOT: PSS/4CFNCS, which shows an impressive performance at high-pressure ranges (sensitivity 0.08 kPa-1 above 44 kPa).

A direct entry to polycyclic quinoxaline derivatives via I2-DMSO mediated oxidative decarboxylation of α-amino acids and the subsequent Pictet-Spengler cyclization reaction.

A facile and highly efficient iodine-promoted strategy has been delineated for the synthesis of indolo and pyrrolo[1,2-a]quinoxaline derivatives via an oxidative Pictet-Spengler type amino cyclo-annulation reaction using ∝-amino acids as aldehyde surrogates. The concomitant benzylic oxidation and the compatibility of different starting materials under standard conditions made the current method versatile. The salient features of the protocol such as readily available starting materials, inexpensive promoters, environmental benignity, broad substrate scope, scalability, and good to excellent yield make the method more attractive to practitioners of organic synthesis.

Investigation of crystal structures, energetics and isostructurality in halogen-substituted phosphoramidates.

A total of 14 compounds, one unsubstituted and 13 halogen-substituted phosphoramidates, have been synthesized from unsubstituted and halogenated (fluoro-, difluoro-, chloro-, bromo-, iodo-substituted) aniline and diphenyl phosphoryl chloride to investigate their molecular assembly in solid-state structures. Amongst them, six groups were formed based on similarities in unit-cell dimensions, space group and molecular assembly of the crystal. The analysis reveals that all the crystal structures contain robust N-H...O hydrogen bonds which are the primary building blocks with ancillary interactions such as C-H...O, C-H...π, C-H...F/Cl/Br/I, F...F, F...π, I...π, Br...π, I...O and Br...O. The role of short and directional C-H...O and C-H...π interactions providing significant stabilization to the densely packed crystalline arrangement is discussed. The contribution of these interactions in stabilizing the crystalline assembly was deduced via computing total interaction energy between dimers and the overall lattice energies using the computer programs Crystal Explorer 17.5 and PIXELC, respectively. Additionally, the occurrence of 3D isostructurality in phosphoradimates and their halogenated analogs was investigated using the XPac program. A comparison of the magnitudes of the torsion angles in the compounds substantiates the role of conformational flexibility in the solid state.

Isolation and Structural Characterization of Regioisomers of Dibrominated Terrylene Diimides.

Diverse applications of rylenediimides are attributed to the accessibility of simple methodologies to obtain versatile halogenated precursors. Terrylene diimides are important molecular platforms to achieve materials with NIR absorption and emission. In this work, we present a simple synthesis for the hitherto unknown di- and tribromo-TDIs. Regioisomerically pure dibromo TDIs, including an elusive 1,14-derivative, could be successfully isolated and structurally characterized along with tribromo-TDI. The utility of these bromo derivatives has also been demonstrated with a redox anchoring.

Interplay of Halogen and Hydrogen Bonding through Co-Crystallization in Pharmacologically Active Dihydropyrimidines: Insights from Crystal Structure and Energy Framework.

A solvent-assisted grinding method has been used to prepare co-crystals in substituted dihydropyrimidines (DHPM) that constitutes pharmacologically active compounds. These were characterized using FT-IR, PXRD, and single-crystal X-ray diffraction. In order to explore the possibility of formation of halogen (XB) and hydrogen bonding (HB) synthons in the solid state, co-crystallization attempts of differently substituted DHPM molecules, containing nitro, hydoxy, and chloro substituents, with different co-formers, such as 1,4-diiodo tetrafluorobenzene (1,4 DITFB) and 3-nitrobenzoic acid (3 NBA) were performed. The XB co-crystals (C2aXB, C2bXB, and C2cXB) prefer the formation of C-I⋅⋅⋅O/C-I⋅⋅⋅S XB synthon, whereas the HB co-crystal (C2dHB) is stabilized by N-H⋅⋅⋅O H-bond formation. Hirshfeld surface analysis revealed that the percentage contribution of intermolecular interactions for XB co-crystals prefer equal contribution of XB synthon along with HB synthon. Furthermore, the interaction energy was analyzed using energy frameworks, which suggests that their stability, a combination of electrostatics and dispersion, is enhanced through XB/HB in comparison to the parent DHPMs.

Structural investigation of methyl 3-(4-fluoro-benzo-yl)-7-methyl-2-phenyl-indolizine-1-carboxyl-ate, an inhibitory drug towards Mycobacterium tuberculosis.

The title compound, C24H18FNO3, crystallizes in the monoclinic centrosymmetric space group P21/n and its mol-ecular conformation is stabilized via C-H⋯O intra-molecular inter-actions. The supra-molecular network mainly comprises C-H⋯O, C-H⋯F and C-H⋯π inter-actions, which contribute towards the formation of the crystal structure. The different inter-molecular inter-actions have been further analysed via Hirshfeld surface analysis and fingerprint plots.

Exploring concomitant/conformational dimorphism in a difluoro-substituted phosphoramidate derivative.

The concomitant occurrence of dimorphs of diphenyl (3,4-difluorophenyl)phosphoramidate, C18H14F2NO3P, was observed via a solution-mediated crystallization process with variation in the symmetry-free molecules (Z'). The existence of two forms, i.e. Form I (block, Z' = 1) and Form II (needle, Z' = 2), was characterized by single-crystal X-ray diffraction, differential scanning calorimetry and powder X-ray diffraction. Furthermore, a quantitative analysis of the energetics of the different intermolecular interactions was carried out via the energy decomposition method (PIXEL), which corroborates with inputs from the energy framework and looks at the topology of the various intermolecular interactions present in both forms. The unequivocally distinguished contribution of strong N-H...O hydrogen bonds along with other interactions, such as C-H...O, C-H...F, π-π and C-H...π, mapped on the Hirshfeld surface is depicted by two-dimensional fingerprint plots. Apart from the major electrostatic contribution from N-H...O hydrogen bonds, the crystal structures are stabilized by contributions from the dispersion energy. The closely related melting points and opposite trends in the calculated lattice energies are interesting to investigate with respect to the thermodynamic stability of the observed dimorphs. The significant variation in the torsion angles in both forms helps in classifying them in the category of conformational polymorphs.