Preorganization in a Cleft-Type Anion Receptor Featuring Iodo-1,2,3-Triazoles As Halogen Bond Donors.

Preorganization via intramolecular hydrogen bonds was applied in a cleft-type receptor by exploiting the excellent halogen bond donor ability as well as hydrogen bond acceptor function of iodo-1,2,3-triazoles. As investigated by isothermal calorimetric titrations, the restriction of conformational freedom causes an enhanced entropic contribution resulting in a strongly increased binding affinity. This efficient way to improve the binding strength of 5-halo-1,2,3-triazoles paves the way for applications of new charge-neutral halogen bond donors in solution.