The electronic structure of a cobalt iron cyanide thin film, Na0.4Co1.3[Fe(CN)(6)]5H(2)O, was switched from Fe-III(low spin)-CN-Co-II(high spin) to Fe-II(low spin)-CN-Co-III(low spin) by exchanging cations in interstitial sites from Na+ to K+. The reverse process was also induced by replacing Na+ with K+. That is, the alkali cations in the interstitial sites dominate the electronic and spin states of the host compound. This type of switching phenomenon can be achieved by choosing a compound with both electronic degeneracy and zeolitic properties.