The changes in the epr and ir spectra of copper(I1)-ammine complexes in a Y-type zeolite have been studied as a function of the amount of ammonia adsorbed. The intensity of the epr spectrum increased linearly until the ratio of the number of ammonia molecules to the number of cupric ions was 4:1, at which point the addition of excess ammonia failed to change the spectrum. The same behavior was noted in the ir spectrum for the symmetric deformation band of ammonia coordinated to cupric ions. Adsorption of deuterated ammonia on a low-exchanged sample produced an epr spectrum which revealed the superhyperfine splitting of four equivalent nitrogen nuclei in the parallel as well as the perpendicular region of the spectrum. These data provide additional evidence that the [Cu(NH3)4I2+complex is formed within the zeolite structure. This complex may be detected in the presence of excess ammonia and oxygen at temperatures up to M O O . The change in the epr spectrum of a moderately exchanged sample upon adsorption of ammonia indicates that the copper ions move out of the small cavities, and most of the complexes are formed in the large cavities of the zeolite.