SHAPE-SELECTIVE MODULATION OF ION-PAIR AND TRIPLE-ION EQUILIBRIA IN ZEOLITES - CHARGE-TRANSFER SALTS OF METHYLVIOLOGEN IODIDES

Zeolites doped with various pyridinium acceptors serve as sensitive color probes for the intracavity assembly of specific ion pairs and ion triplets. For example, the ion exchange of the methylviologen dication (MV2+) into sodium zeolite-Y can be carefully regulated to produce MV(1.0)Y and MV(2.0)Y containing one and two MV2+, respectively, in each (average) supercage. The highly efficient intercalation of iodide from acetonitrile solution then affords a series of brilliantly colored zeolites, the diffuse reflectance spectra of which reveal the presence of characteristic charge-transfer (CT) bands of the methylviologen iodides extant as the ion pair MV2+(I-) and the ion triplet MV2+(I-)2. Shape selectivity in such a stepwise assemblage of ions within the supercage is controlled by the size of the iodide salt M+I- (where M+ = Na+, K+, (CH3)4N+, (CH3CH2)4N+, (CH3CH2CH2CH2)4N+, etc.) which effectively limits the penetration of the zeolite aperture.