CHARACTERIZATION OF NAY ZEOLITE-ENCAGED TETRAIRIDIUM CLUSTERS BY INFRARED AND X-RAY-ABSORPTION SPECTROSCOPIES

[Ir(CO)2(acac)] in the pores of NaY zeolite was treated in CO and converted into [Ir4(CO)12]. The zeolite-encaged [Ir4(CO)12] was characterized by infrared and extended X-ray absorption fine structure spectroscopies, with the data indicating an average Ir-Ir coordination number of 2.6 and an average Ir-Ir distance of 2.69 angstrom, in agreement, within the experimental error, with the published crystallographic data for solid [Ir4(CO)12]. Structurally simple zeolite-encaged iridium clusters were made by decarbonylation of the [Ir4(CO)12] at 325-degrees-C in flowing He followed by H-2. The decarbonylated clusters had an average Ir-Ir coordination number of 3.4 and a bond distance of 2.70 angstrom, consistent with the inference that the tetrahedral framework structure of [Ir4(CO)12] had been retained after decarbonylation; thus, the cluster is represented as tetrahedral Ir4. Infrared spectra showed that [[Ir4(CO)12] was re-formed when the sample was treated in CO at 60-degrees-C.