SHAPE-SELECTIVE ASSEMBLAGE OF CHARGE-TRANSFER COMPLEXES WITHIN CHANNEL-TYPE ZEOLITES

The channel-type zeolites (mordenite, zeolite-L and mazzite) with different-sized pores are uniformly ion exchanged with a series of pyridinium cations (A+) of various sizes and shapes. Intercalation of these pyridinium-doped (colorless) zeolites with aromatic donors (D) of differing sizes and shapes leads to brightly colored zeolites, in which the diffuse reflectance spectra reveal characteristic charge-transfer bands of the intermolecular complex [A+,D], encapsulated in the zeolite channel. The selective production of colored zeolites that depends on the size/shape of the pyridinium cation and the aromatic donor, as well as the pore size, thus defines the shape selectivity of the channel zeolites. The restricted (cylindrical) cavity of channel zeolites to act as shape-selective hosts to various charge-transfer complexes is compared to the large (spherical) supercage of the more common zeolite-Y.