Self-selected formation of single discrete supramolecules with flexible, bidentate ligands in the coordination-driven self-assembly

Flexible donor ligands like 1,2-bis(3-pyridyl)ethyne or 1,4-bis(3-pyridyl)-1,3-butadiyne self-assemble into discrete 2-D supramolecules instead of infinite networks upon combination with organoplatinum 90, 120, and 180 degree acceptor units. These systems are unique examples of versatile pyridine donors adjusting their bonding directionality to accommodate rigid platinum acceptors in the formation of closed macrocycles. Discrete, nanoscopic 3-D cages are also prepared in high yield via coordination-driven self-assembly from bidentate 3-substituted pyridines and tripod organoplatinum acceptors. Flexible, bidentate 3-substituted pyridine donors and a rigid organopalladium acceptor are also exclusively self-assembled into discrete 2-D macrocycles. Moreover, discrete supramolecules are successfully prepared from ambidentate donor ligands and platinum containing acceptors. Despite the possibility of forming more than one product, ambidentate ligands prefer to self-assemble predominantly into one species. Flexible, ambidentate pyridyl-carboxylate based donor ligands like sodium 3-(3-pyridyl)benzoate, sodium 4-(3-pyridyl)benzoate and potassium 4-(3-pyridyl)ethynylbenzoate self-assemble into discrete [2+2] macrocyclic species instead of infinite networks when combined with a 90 degree organoplatinum acceptor. In each case only one isomeric ensemble is selectively formed in high yield. All products are characterized by electrospray ionization mass spectrometry (ESI-MS), ³¹P{¹H} and ¹H NMR spectroscopy. They are the first examples of discrete supramolecules incorporating flexible, bidentate donor ligands. Despite their potential versatility, these flexible donors adjust their bonding directionality to accommodate a rigid acceptor in the formation of one discrete ensemble.