Spontaneous Resolution of an Electron-Deficient Tetrahedral Fe4L4 cage

A highly electron-deficient C-3-symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)(2), thereby resulting in the homochiral assembly of a new family of robust tetrahedral M4L4 cages. This homochiral T-symmetric cage containing a relatively large cavity of 330 angstrom(3) is capable of encapsulating an anionic guest, as was determined by mass spectrometry, F-19 NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH3CN led to crystals containing both (Delta Delta Delta Delta and Lambda Lambda Lambda Lambda) enantiomers, while crystallization from CH3OH resulted in crystals containing only the right-handed (Delta Delta Delta Delta) cage. The difference in the crystal packing of the two crystal structures is discussed and a feasible explanation for the unique phenomenon among supramolecular cages-spontaneous resolution-is given.