Zeolite-encaged iridium clusters with hydride ligands: Characterization by extended X-ray absorption fine structure, NMR, and inelastic neutron scattering vibrational spectroscopies

A family of NaY zeolite-supported iridium clusters was prepared by reductive carbonylation of Ir(CO)₂(acac) sorbed in the zeolite pores to form Ir₆(CO)¹⁶, which was decarbonylated by treatment in He. This method allowed preparation of samples with Ir contents as high as 33.0 wt.%. Extended X-ray absorption fine structure spectra of the decarbonylated samples indicate that the clusters are well approximated as octahedral Ir₆ in the zeolite cages. The high loadings of clusters in the zeolite allowed characterization of the hydride ligands on the clusters by ¹H NMR spectroscopy and inelastic neutron scattering spectroscopy. These ligands exist on the clusters even in the absence of H₂ in the gas phase, presumably equilibrated with OH groups on the zeolite. The data indicate both terminal and bridging hydride ligands on the clusters. The H/Ir atomic ratio is estimated to be approximately 0.01 on the basis of the ¹H NMR data and thermogravimetric analysis of the sample.