Unique halogen-π association detected in single crystals of C-N atropisomeric N-(2-halophenyl)quinolin-2-one derivatives and the thione analogue.

In single crystals of C-N atropisomeric N-(2-halophenyl)quinolin-2-one and the thione analogue, a unique association based on a halogen-π interaction was detected. In racemic and optically pure N-(2-bromo- or 2-chlorophenyl)quinolin-2-ones, homochiral layered polymers, which consist of (P)- or (M)-atropisomers, were formed through intermolecular halogen-π association. The halogen-π association in the racemates is due to a halogen bond (C-X···π) between a σ-hole on the halogen atom and a π-electron on the quinolinone benzene ring, while that in optically pure forms is caused by an n-π* interaction between a lone electron pair on the halogen atom and a π* orbital of the quinolinone. In contrast to the formation of the homochiral layered polymer in quinolinones, in racemic N-(2-bromophenyl)quinoline-2-thione, heterochiral layered polymers, in which (P)- and (M)-atropisomers were alternately connected, were formed through an n-π* interaction between a lone electron pair on the bromine atom and a π* orbital of the quinoline-2-thione.