[Ir(CO)(2)(acac)] in the pores of NaX zeolite was treated in CO and converted into iridium carbonyl clusters, which are suggested on the basis of infrared spectra and comparisons with solution chemistry to be [HIr4(CO)(11)](-), which was subsequently converted into clusters that are suggested to be [Ir-6(CO)(15)](2-). The former clusters in the NaX zeolite were decarbonylated by treatment in He followed by H-2 at 573 K and characterized by extended X-ray absorption fine structure spectroscopy. The Lr-lr first-shell coordination number (3.0) indicates that the clusters were predominantly Ir-4 tetrahedra. The clusters postulated to be[Ir-6(CO)(15)](2-) were reversibly fragmented and reformed in the cages.