The Janus-like behaviour of sulfur in substituted diquinoline inclusion crystal structures

Abstract

The crystal structures of the methylene-bridged diquinolines 1,2 are compared to those of their newly synthesised thia-substituted analogues 9,10. As expected from our molecular design, neither non-brominated compound 1 nor 9 shows inclusion properties, but the dibrominated structures 2 and 10 act as versatile lattice inclusion host molecules. All our crystal structures of the methylene-bridged compounds 1,2 contain an (EF)₆ centrosymmetric dimeric building block, built from three different types of aryl edge-face (EF) interactions. The crystal structures of the thia-compounds 9,10 also involve (EF)₆ dimers, but fall into two distinct types. In one group, the sulfur atom effectively mimics the methylene group and isostructural compounds result across the two series. The second group is comprised of structures that are markedly dissimilar between the two series, even though the sulfur substituent does not play an overt role in the molecular packing. These similarities and differences are examined in crystal engineering terms.