New proton-sponge-like macrocyclic compound: Synergistic hydrogen bonds of aminopyridine

N,N',N-Tris(p-tolyl)azacalix[3](2,6)pyridine (1) that shows a high proton affinity (pK(BH+) = 23.1 in CD3CN) has been classified as a new type of proton-sponge-like compound. X-ray crystallography reveals that 1 is ideal for accommodating a single proton in its cavity. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).