Xe-129 NMR spectroscopy of metal carbonyl clusters and metal clusters in zeolite NaY

[Ir-4(CO)(12)] and [Ir-6(CO)(16)] were synthesized in the pores of zeolite NaY by reductive carbonylation of sorbed [Ir(CO)(2)(acac)], and [Rh-6(CO)(1 6)] was similarly synthesized from [Rh(CO)(2)(acac)], The supported metal c arbonyl clusters were decarbonylated to give supported clusters modeled on the basis of extended X-ray absorption fine structure spectra as Ir-4, Ir-6 , and Rh-6, respectively. The supported metal carbonyl clusters and the sup ported metal clusters formed by their decarbonylation were investigated by Xe-129 NMR spectroscopy at temperatures in the range of 100-305 K. As the t emperature increased, the chemical shift decreased. The curves representing the chemical shift as a function of temperature for xenon sorbed on the ze olite that contained clusters modeled as Ir-4, Ir6, and Rh-6 were all essen tially the same and hardly different from that observed for the bare zeolit e NaY. This comparison leads to the conclusion that xenon is less strongly adsorbed on the decarbonylated metal clusters than on the zeolite framework . Larger chemical shifts were observed for the zeolites containing the meta l carbonyl clusters, with the largest being observed for the zeolite contai ning [Ir-4(CO)(12)] These results are explained on the basis of the cluster sizes and NaY zeolite geometry. We suggest that the contact between xenon and [Ir-4(CO)(12)] cluster is better than that between xenon and [Ir-6(CO)( 16)] or xenon and [Rh-6(CO)(16)] clusters because these two larger clusters almost fill the zeolite supercages and exclude xenon, whereas [Ir-4(CO)(12 )] in the supercages is small enough to allow entry of the xenon.