Quantitative Investigation of Polymorphism in 3-(Trifluoromethyl)-N-[2-(trifluoromethyl) phenyl] benzamide

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Assessing the Significance of Hexafluorobenzene as a Unique Guest Agent through Stacking Interactions in Substituted Ethynylphenyl Benzamides

A series of differently substituted host molecules have been employed to systematically investigate the nature and strength of the stacking interactions with hexafluorobenzene in the solid state. The hexafluorobenzene guest binds to the crystal lattice of the parent compound, the <i>N</i>-ethynylphenyl benzamide host and its nine other halogenated (-F/-CF3/-Cl/-Br at ortho/meta/para positions individually) analogues via stacking of aromatic rings. The geometrical and energetic features of intermolecular interactions in host–guest molecules have been investigated, and the results elucidate the dominancy of dispersion in the stabilization of the aryl-hexafluorobenzene stacking, while the electrostatic component also plays an important role. The plots of the molecular electrostatic potential provide a fundamental basis of the electrostatic complementarity that exists in between the host and the guest. The topological characterization reveals unambiguous evidence for the direct participation of the substituents in closed-shell bonding interactions with the aromatic rings at the local geometry, which remarkably controls the nature and energetics of such motifs. Additionally, the observed upfield 19F NMR chemical shifts for perfluorinated guest upon complexation with the host compounds provide evidence for the existence of the host–guest stacking interaction also in the solution state

Structural mapping of mechanically flexible photoluminescent and photodynamic molecular crystals

Mechanically flexible luminescent organic crystals have become an essential part of modern technologies like optoelectronics, while photoluminescent crystals, able to transform light energy into mechanical motions, are a promising choice for actuating and photonic devices. Here, we present our findings on how quantitative structural mapping can rationalize the change in phosphorescence emission, as a function of the flexibility of elastic single crystals of dibenzothiophene and its brominated derivate. The dibenzothiophene crystals show dual fluorescence (FL) and room temperature phosphorescence (RTP), while the bromo derivative only shows RTP. We further present how the photosalient behavior of room temperature phosphorescent molecular crystals, based on organoboron containing Lewis acid-base adducts, can be explained by crystal-to- crystal [2+2] cycloaddition reactions as the driving force. The latter crystals display short-lived room temperature phosphorescence, while the photodynamic events are accompanied by enhancement of their phosphorescence intensity

Silicone Oil Induced Spontaneous Single-Crystal-to-Single-Crystal Phase Transitions in Ethynyl Substituted <i>ortho</i>- and <i>meta</i>-Fluorinated Benzamides

We present an unusual observation of facile single-crystal-to-single-crystal phase transition induced in hydrophobic silicone oil at ambient conditions which is fast in <i>ortho</i>-fluoro substituted ethynyl phenyl benzamide and relatively slow for the <i>meta</i>-isomer. These phase transitions are also observed in crystals, on heating, at high temperature, and in the absence of silicone oil. The extensive thermal and structural analyses reveal that the phase transition between the two polymorphs of the <i>ortho</i>-isomer is monotropic in nature and involves large supramolecular rearrangements, wherein for the <i>meta</i>-isomer the same is enantiotropic and is driven by altered molecular conformations. The structural features demonstrate the absence of prevalent and strong NH···OC hydrogen bonds in the crystal structures of both polymorphs of the <i>ortho</i>-fluoro substituted benzamide. A plausible molecular mechanism based on energetically favored “structural motifs” has been proposed which depicts that rotational and translational motion between the molecules present in the crystal relates molecular motifs and provides a rationale for the origin of the nucleation and growth process during the phase transition

Observation of Rapid Desolvation of Hexafluorobenzene Involving Single-Crystal-to-Single-Crystal Phase Transition in a Nonporous Organic Host

We report an unusual occurrence of an extremely fast single-crystal-to-single-crystal phase transition induced by rapid desolvation of hexafluorobenzene at room temperature mediated by a subtle interplay of π···π stacking interactions in <i>N</i>-(3-ethynylphenyl)-4-fluorobenzamide. The nature of the host–guest stacking interaction has been explored in terms of interaction energy, electrostatic complementarity, and topological analysis with the inputs from reduced density gradient-noncovalent interactions fingerprint descriptor. Furthermore, the compound also exists in two other nonsolvated polymorphic forms

Effect of chemical substitution on the construction of boroxine-based supramolecular crystalline polymers featuring B←N dative bonds

We report the mechanochemical synthesis of five single-crystalline phenylboroxine and 1,4-diazabicyclo[2.2.2]octane (DABCO) ligand-based adducts, directed by boron-nitrogen dative bonds. By tuning the electronic features of the phenylboroxines by chemical modifications (-H/-OMe/-F/-Cl/-Br) at the para-position, the formation of the resulting bicomponent adducts can be controlled to obtain molecular to 1D polymeric crystalline materials. The electrostatic and quantum topological aspects of the B <- N bonds reveal the origin for the different binding modes of the boroxine-DABCO adducts yielding molecular to polymeric structures

Photomechanical Motions in Organoboron-Based Phosphorescent Molecular Crystals Driven by a Crystal-State [2 + 2] Cycloaddition Reaction

Photoluminescent molecular crystals integrated with the ability to transform light energy into macroscopic mechanical motions are a promising choice of materials for both actuating and photonic devices. However, such dynamic photomechanical effects, based on molecular organoboron compounds as well as phosphorescent crystalline materials, are not yet known. Here we present an intriguing example of photomechanical molecular single crystals of a newly synthesized organoboron containing Lewis acid–base molecular adduct (BN1, substituted triphenylboroxine and 1,2-di(4-pyridyl)ethylene) having a capsule shape molecular geometry. The single crystals of BN1 under UV light exhibit controllable rapid bending–shape recovery, delamination, violent splitting–jumping, and expanding features. The detailed structural investigation by single-crystal X-ray diffraction and 1H NMR spectroscopy reveals that the photosalient behavior of the BN1 single crystals is driven by a crystal-to-crystal [2 + 2] cycloaddition reaction, supported by four donor–acceptor type B←N bonds. The instant photomechanical reaction in the BN1 crystals occurs under UV on account of sudden release of stress associated with the strained molecular geometry, significant solid-state molecular movements (supramolecular change), and cleavage of half intermolecular B←N linkages to result in a complete photodimerized single-crystalline product via the existence of two other intermediate photoproducts. In addition, the BN1 crystals display short-lived room temperature phosphorescence, and the photodynamic events are accompanied by the enhancement of their phosphorescence intensity to yield the photoproduct. Interestingly, the molecular crystals of the final photoproduct polymerize at ambient conditions when recrystallized from the solution forming a 2D supramolecular crystalline polymer stabilized by the retention of all B←N coordination modes

Quantitative Investigation of Polymorphism in 3‑(Trifluoromethyl)‑<i>N</i>‑[2-(trifluoromethyl)phenyl]benzamide

The occurrence of concomitant dimorphism has been observed in the case of trifluoromethyl substituted benzanilide, namely, 3-(trifluoromethyl)-<i>N</i>-[2-(trifluoromethyl)­phenyl]­benzamide, wherein both forms show the presence of a multiple number of molecules in the asymmetric unit (<i>Z</i>′ > 1). Thermal studies confirm the “extremely rare occurrence” of simultaneous melting and solid-to-solid phase transition at the same temperature from centrosymmetric, <i>Z</i>′ = 2 structure (triclinic, <i>P</i>1̅, form I) to noncentrosymmetric, <i>Z</i>′ = 4 structure (monoclinic, <i>Cc</i>). Both forms exhibit similar density and lattice energy. Conformationally different molecules in the asymmetric unit in both the high-<i>Z</i>′ structures are observed to be connected with strong N–H···OC and weak C–H···OC hydrogen bonds. The dissimilarities in the crystal packing were analyzed by Xpac method, and the molecule–molecule interaction energies were evaluated by the PIXEL method. The results revealed the presence of 2D isostructurality between the two forms which mainly consists of the most stabilized intermolecular interactions (namely, strong N- H···OC, C–H···OC, and C–H···π hydrogen bonds) in their crystal packing while differences in their crystal packing are mainly on account of the presence of weak C–H···F–C­(sp³) hydrogen bond and C­(sp³)–F···F–C­(sp³) interactions