CH/? hydrogen bonds in crystals

TLDR

The CH/π interaction is a weak hydrogen bond between a CH group and a π‑system, analogous to other weak forces such as CH/O and OH/π interactions. This review examines the consequences of CH/π hydrogen bonds in supramolecular chemistry. It analyzes these interactions across intramolecular contacts, crystal packing, host–guest complexes, lattice‑inclusion clathrates, enantioselective clathrate formation, catalytic enantioface discrimination, and solid‑state photoreactions. CH/π interactions have clear implications for crystal engineering and drug design.

Abstract

The nature and characteristics of the CH/π interaction are discussed by comparison with other weak molecular forces such as the CH/O and OH/π interaction. The CH/π interaction is a kind of hydrogen bond operating between a soft acid CH and a soft base π-system (double and triple bonds, C6 and C5 aromatic rings, heteroaromatics, convex surfaces of fullerenes and nanotubes). The consequences of CH/π hydrogen bonds in supramolecular chemistry are reviewed on grounds of recent crystallographic findings and database analyses. The topics include intramolecular interactions, crystal packing (organic and organometallic compounds), host/guest complexes (cavity-type inclusion compounds of cyclodextrins and synthetic macrocyclic hosts such as calixarenes, catenanes, rotaxanes and pseudorotaxanes), lattice-inclusion type clathrates (including liquid crystals, porphyrin derivatives, cyclopentadienyl compounds and C60 fullerenes), enantioselective clathrate formation, catalytic enantioface discriminating reactions and solid-state photoreaction. The implications of the CH/π concept for crystal engineering and drug design are evident.