Acid Inclusion Properties of Helical Self-Assembly of a 5,5′-Biquinoline Derivative

With a view to understand the stacking of anions in the folds of the helical self-assembly, a new organic helical 5,5′-biquinoline derivative, bis-5,5′-[2-(quinolin-8-ylamino)ethanol], having a hydroxyl pendent group attached through a flexible ethylene tether is synthesized through a manganese(II) catalyzed C–C bond formation reaction. The compound adopts a helical structure with a dihedral angle between two planes of quinoline rings as 60.08° and self-assembles with the aid of hydoxy groups and nitrogen atoms in the quinoline rings along with C–H···O interactions. The helical self-assembly of bis-5,5′-[2-(quinolin-8-ylamino)ethanol] can encapsulate guests of two different shapes, namely trigonal planar (nitrate) and tetrahedral (perchlorate), without significantly losing its original helicity. Interactions of this helical molecule with perchloric acid and nitric acid are found to be similar in solution; however, in solid state perchloric acid forms its salt while nitric acid forms a co-crystal with it.