By utilizing the idea of Coordination Programming, postsynthesis modification of a porous ionic crystal K-2[Cr3O-(OOCH)(6)(mepy)(3)](2)[alpha-SiW12O40]center dot 8H(2)O (mepy: 4-methylpyridine) (1) proceeded in a single-crystal-to-single-crystal manner. Basicities of the pyridine derivatives and potassium salts were keys to the selective formation of [Cr3O(OOCH)(6)(mepy)(2)-(H2O)](+) as a macrocation. Results of the alcohol sorption isotherms showed that the sorption capacity increased almost twice without changes in the size of the channel opening by the postsynthesis modification.