Halogen substituted quinolylsalicylaldimines: Four halogens three structural types

A series of halogen substituted 5-X-N-(8-quinolyl)salicylaldimines (HqsalX, X = F 1, Cl 2, Br 3 and I 4) have been prepared, characterized and the crystal structures of all four are reported. The compounds form stacks, in most cases held together either by π–π or lone pair(N)–π interactions. All compounds exhibit an intramolecular OH⋯N hydrogen bond with 2 also displaying an intermolecular OH⋯O hydrogen bonding square. Additional CH⋯N/O and CH⋯π interactions serve to link neighbouring HqsalX molecules with 3 and 4 forming narcissistic dimers. While the halogen has a profound effect on the structure it is not involved in either hydrogen or halogen bonding in any of the structures. DFT calculations suggest that the conformational preference is dependent on the halogen.

► The structures of four halogen substituted quinolylsalicylaldimines are reported.
► The structures exhibit hydrogen bonds, π–π and CH⋯N/O interactions.
► The chloro derivative features an unexpected ‘inverted’ conformation.
► The conformation determines the strength of the hydrogen bond.
► DFT calculations indicate conformational preferences are halogen dependent.