Short C–H⋯F interactions involving the 2,5-difluorobenzene group: understanding the role of fluorine in aggregation and complex C–F/C–H disorder in a 2 × 6 isomer grid

Abstract

A 26 isomer grid of six N-(difluorophenyl)benzamides (F 2 -xx) and six N-(phenyl)difluorobenzamides (xx-F 2 ) (xx = 23/24/25/26/34/35) integrating crystal structure analyses (at 294 K), gas phase calculations and conformational analyses is reported. All 12 isomers (C 13 H 9 N 1 O 1 F 2 ) aggregate via N-HO=C intermolecular interactions and usually in combination with intermolecular C-HO/F/ interactions and often FF contacts. The F 2 -25 crystal structure has a remarkably supershort intermolecular C-HF interaction for a neutral organic, while the 25-F 2 (amide-bridged reversed) has an analogous short C-HF in a twinned, disordered structure. The results demonstrate a promising 2,5-difluorobenzene effect being responsible for shorter C-H…F contacts than would normally be expected. An understanding of the relationships between F/H atom permutations in substituted difluorobenzenes is realised with the influence of fluorine substitution patterns on molecular aggregation rationalised in a series of twelve isomers. 16 Scheme 1 The (26) F 2 -xx and xx-F 2 isomer grids.

Postsynthetic Framework Contraction Enhances the Two-Photon Absorption Properties of Pillar-Layered Metal–Organic Frameworks

“…Nevertheless, a comparison of the ligand geometries in the investigated MOFs reveals that the disorder of the TPE core and one external phenylene ring in 1-F is analogous to that of 1 , which means that the fluorine atoms exert minor intramolecular steric effects on the relative changes of ligand geometry in the case of the noncontracted networks (see Figure S22). Furthermore, looking into the type of intermolecular interactions between subframeworks in 1 and 1-F , the crystal structures show the presence of several weak π···H–C arom and F···H–C arom interactions (characteristic distances from 2.09 to 2.84 Å). − …”

Probing the Electronic Properties and Interaction Landscapes in a Series of N-(Chlorophenyl)pyridinecarboxamides

“…In related research, we have considered the competition between the F, O=C, N–H, and aromatic rings in terms of influencing interactions and aggregation. 36 We have also speculated on the number of halogen atoms and type of halogen atom needed to tip the interactions from hydrogen bonding toward halogen bonding of the type C–Cl···O=C, C–Cl···N pyridine , and C–Cl···Cl–C. Indeed, research studies on the competition between interactions in crystal structure formation have been pursued with much interest recently in structural systematic studies of extensive series of molecules and in co-crystal formation.…”

“… 14 − 32 Extensive structural studies have been undertaken on series of organohalogens. Examples include the investigation of fluorine in benzamides 33 − 36 and potential uses of bromine and iodine in agrochemicals. 37 − 39 …”

“…4 , 47 , 48 In tandem with drug development, there has been a surge in the study and use of halogens in new drugs and especially fluorine and chlorine in pharmaceuticals. 33 − 36 , 40 − 46 …”

A New Protocol for the Synthesis of New Thioaryl-Porphyrins Derived from 5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin: Photophysical Evaluation and DNA-Binding Interactive Studies

“…These observations indicate that the substituent groups do not significantly interfere in the interactions, despite compound 3d (which possesses the ortho -amino group) presenting more H-bonds with the DNA. In addition, we observed the importance of the carbon-hydrogen bond with the fluorine moiety (C-H···F-C) [ 46 , 47 , 48 , 49 ] as an interaction that stabilizes the thioaryl-porphyrins-DNA adduct. The predicted theoretical thermodynamic data (∆G bind ) indicated that all the thioaryl-porphyrin derivatives present spontaneous interaction with DNA fragments ( 3a (−8.8 kcal/mol); 3b (−9.3 kcal/mol); 3c (−9.3 kcal/mol); 3d (−8.8 kcal/mol)).…”