No abstract

Os 5 C(CO) 14 ] 2was synthesized in 65% yield on the surface of MgO by treatment of adsorbed [Os 3 (CO) 12 ] in CO. High-resolution transmission electron microscopy (HRTEM) indicated that the nanoclusters were nearly monodisperse and in the size range consistent with [Os 5 C(CO) 14 ] 2-. The supported [Os 5 C(CO) 14 ] 2was decarbonylated in helium, giving supported nanoclusters that are well approximated as Os 5 C, as shown by HRTEM and EXAFS data. Decarbonylation in H 2 gave larger clusters of osmium, as shown by HRTEM.

[Ir4(CO)12] and [Ir6(CO)16] were synthesized in the pores of zeolite NaY by reductive carbonylation of sorbed [Ir(CO)2(acac)], and [Rh6(CO)16] was similarly synthesized from [Rh(CO)2(acac)]. The supported metal carbonyl clusters were decarbonylated to give supported clusters modeled on the basis of extended X-ray absorption fine structure spectra as Ir4, Ir6, and Rh6, respectively. The supported metal carbonyl clusters and the supported metal clusters formed by their decarbonylation were investigated by 129Xe NMR spectroscopy at temperatures in the range of 100−305 K. As the temperature increased, the chemical shift decreased. The curves representing the chemical shift as a function of temperature for xenon sorbed on the zeolite that contained clusters modeled as Ir4, Ir6, and Rh6 were all essentially the same and hardly different from that observed for the bare zeolite 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 metal carbonyl clusters, with the largest being observed for the zeolite containing [Ir4(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 [Ir4(CO)12] cluster is better than that between xenon and [Ir6(CO)16] or xenon and [Rh6(CO)16] clusters because these two larger clusters almost fill the zeolite supercages and exclude xenon, whereas [Ir4(CO)12] in the supercages is small enough to allow entry of the xenon.