IRIDIUM CLUSTERS IN NAX ZEOLITE CAGES - SYNTHESIS, REACTIVITY, AND CHARACTERIZATION BY INFRARED AND EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPIES

[Ir(CO)(2)(acac)] in the pores of NaX zeolite was treated in CO and co nverted into iridium carbonyl clusters, which are suggested on the bas is 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 spect roscopy. The Lr-lr first-shell coordination number (3.0) indicates tha t the clusters were predominantly Ir-4 tetrahedra. The clusters postul ated to be[Ir-6(CO)(15)](2-) were reversibly fragmented and reformed i n the cages.