Coplanar recognition by a Rebek cleft is provided by cooperative structural effects involving a combination of O-H center dot center dot center dot O, O-H center dot center dot center dot N, and C-H center dot center dot center dot O forces

[GRAPHICS] Reaction of 2,7-di-tert-butyl-9,9-dimethyl-4,5-xanthenedicarboxylic acid (1 ), a Rebek cleft, with 1,2-trans-bis(2-pyridyl)ethylene (2) yields a three- component organic assembly, 2(1)(.)2 (3), of nanoscale dimensions that is h eld together by 10 cooperative O-H . . .N, O-H . . .O, and C-H . . .O hydro gen bonds. The cleft adopts a planar conformation, by forming an intramolec ular O-H . . .O hydrogen bond, which enables the host to recognize the gues t in a coplanar orientation that facilitates the cooperativity displayed by the multiple forces.