Self-Assembly Behavior Shifting to Crystal Formation of Chiral Macrocyclic Tetraimines

The enantiopure macrocyclic tetraimines containing adamantane moieties (1, 2) were synthesized from (R,R)- or (S,S)-1,2-cyclohexanediamine and a disubstituted adamantane derivative having salicylaldehyde in moderate yield. Single crystals (1a) were obtained from a methanol/ chloroform mixture and 1. X-ray crystallographic analysis revealed that the macrocycles had a rhomboidal structure and were arranged into a molecular network bearing layer structures through CH center dot center dot center dot O and CH center dot center dot center dot pi interactions. Racemic crystals (1.2-a) were formed from crystallization of 1 and 2 in a 1:1 stoichiometry. The macrocycles had a rhomboidal framework with a longer axis, and 1 and 2 were alternatively aligned into the molecular network composed of columnar structures by CH center dot center dot center dot pi and CH center dot center dot center dot O interactions. Macrocycle 1 self-assembled into spheres, and their fused fibrous and network aggregates, and eventually were translated into crystals. Meanwhile, the mixing of both enantiomers 1 and 2 at a ratio of 1:1 afforded racemic crystals by way of similar self-assembled structures under identical conditions; however, the rate of crystal formation was faster than that of 1.