Supramolecular Packing of a Series of N-Phenylamides and the Role of NH···O=C Interactions

A series of seven N-phenylamides [R-C(O)NHPh, in which R: CH₃, C(CH₃)₃, Ph, CF₃, CCl₃, CBr₃, and H] were used as models in this study. Molecular packing and intermolecular interactions were evaluated by theoretical calculations, solution NMR, and quantum theory of atoms in molecules analyses. Crystallization mechanisms were proposed based on the energetic and topological parameters using the supramolecular cluster as demarcation. Concentration-dependent ¹H NMR experiments corroborated the proposed interactions between molecules. For all compounds (except for R: H, which initially formed tetramers), layers (two-dimensional) or chains (one-dimensional) were formed in the first stage of the proposed crystallization mechanisms. The presence of strong intermolecular NH···O=C interactions promoted the first stages. The study in solution provided different values of association constant (K _ass) governed by the hydrogen bond NH···O=C, showing that the stronger interactions are directly influenced by the substituent steric hindrance. A correlation between K _{ass(NH···O=C)} from the solution and the NH···O=C interaction energy in the crystal showed a good trend.

Similarities and differences in the crystal packing of halogen-substituted indole derivatives

The role of different intermolecular interactions in the crystal structures of halogen-substituted indoles which are fused with six-membered or seven-membered cyclic rings is investigated here. Several crystal structures show isostructural characteristics due to the presence of similar supramolecular motifs. In the absence of any strong hydrogen bonds, the molecular packing of reported structures is primarily stabilized by the presence of non-classical N-H...π and C-H...π interactions in addition to C-H...X (X = F/Cl/Br) interactions. The nature and energetics of primary and secondary dimeric motifs are partitioned into the electrostatics, polarization, dispersion and exchange-repulsion components using the PIXEL method. Short and directional N-H...π interactions are further explored by a topological analysis of the electron density based on quantum theory of atoms in molecules.

Quantitative analysis of weak non-covalent interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles

A detailed experimental and theoretical investigation on the intermolecular interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles is reported and different π staking motifs observed in these structures.