¹²⁹Xe NMR Spectroscopy of Metal Carbonyl Clusters and Metal Clusters in Zeolite NaY

Abstract

[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.

Catalysis Science and Technology

“…The results have indicated relative preferences for Xe interactions with the walls of the zeolite vs. metal clusters of differing sizes within the constrained microporous environment. [8] 2). ln our exploration of the structure of site-isolated oxidation catalysts, we have used theoretical chemistry studies to probe the features of Co ions in inorganic frameworks, specifically the nanoporous aluminum phosphates, and the interaction of dioxygen (Oz) with the Co.…”

129Xe on Ir(111): NMR study of xenon on a metal single crystal surface

“…The obtained shift anisotropy is an ϭ 291 ppm or ⌬ ϭ 437 ppm. The xenon shift measurements on small iridium and rhodium clusters already mentioned (29) show little line broadening and thus small anisotropies even at 100 K. The anisotropy resulting from Xe-Xe interaction is by far not large enough (see above). In restricted geometries (cages and channels) rather large anisotropies have been seen (35); the largest being in clathrates of almost 200 ppm (36).…”

“…Xenon interacting with small isolated clusters (Ir 4 and Ir 6 ) shows shifts between 100 and 140 ppm, indicative of physisorption (29). The linewidth observed is Ͻ20 ppm.…”

Robust Microporous Monoliths with Integrated Catalytically Active Metal Sites Investigated by Hyperpolarized 129Xe NMR

“…44 It has not only been proven sensitive to the changes in amorphous polymer structure with cross-linking, 45 but also has been shown to be useful in the characterization of paramagnetic metal particles confined within zeolites with varying cluster size. 46,47 Here, we use 129 Xe NMR as a tool to monitor the subsequent effects of Ni-particle inclusion on the internal surfaces of the hybrid nanocomposite material.…”