A statistical survey of the Cambridge Structural Database reveals that the interaction between the π-holes of nitro groups and electron-rich atoms is somewhat directional. High-level ab initio computations indicate energies up to −6.6 kcal mol⁻¹.

This highlight article summarizes some of the fundamental aspects of the anion–π interaction leading to several design strategies for generating it in solids. In the main body we highlight some relevant examples that illustrate the viability of these strategies and the importance of anion–π interactions in crystal engineering.

A combined CSD and ab initio study reveals that the interaction between the sp³ C-atom in para-substituted ArCF₃ and electron rich atoms is weak (<5 kcal mol⁻¹), somewhat directional, and thus comparable to CH–π interactions.

A novel procedure for the thorough analysis of intermolecular interactions from structural data found in the Cambridge Structural Database has been developed, which takes into account the amount of space occupied by the interacting partners. Hence, volume-corrected probability distribution plots and relative abundance plots have been generated for molecule⋯ElR pairs (where molecule is a p-X-phenyl group with X = CH₃, F, Cl, Br, I or dichloromethane, and ElR stands for electron-rich atom, i.e. halogen, N, O, P, S, As, Se or Te), which clearly show the highly directional nature of halogen bonding and its potential competitiveness with hydrogen bonding.