Molecular structure of Rebek's diacid-quinoxaline: confirmation of two-point binding

The single crystal X-ray structure of a 1:1 complex of Rebek's diacid and quinoxaline (2), conclusively identified two-point binding as the mode of complexation. Gradual evaporation of an ethanol solution of diacid 1 having a surplus of quinoxaline, was used to obtain the cystals of 2. They were triclinic, and the asymmetric unit had a pair of cystallographically independent molecules of the complex 2, A and B. Nearly symmetric, syn, two-point binding of quinoxaline was observed for both A and B.