Metal guests, confinement

Chemical and Spectroscopic Probes of Internal Versus External Confinement of Metal Guests... 

The process of loading zeolites with organometallie complexes always brings to the forefront the question of internal versus external confinement of the metal guest. In this paper we present some experiments based on size exclusion, metal loading and intrazeolite chemistry which in conjunction with FT-FAR-IR, EPR and UV-visible reflectance spectroscopy, critically probe the question of internal versus external location for the case of five representative organometallics,... 

Thus by using Co2(C0)8 as a representative organometallic guest, and a combination of size exclusion experiments and intrazeolite oxidation chemistry, as probed through the far-IR cation spectra of sodium and acid faujasites and A-zeolites, one is able to distinguish between internal and external confinement of the metal guest(s) in the zeolite. 

These results suggest that MOFs as extended metal-organic assemblies could show a similar host-guest chemistry. In uncharged MOFs however, space confinement should be the most effective stabilizing effect on these species. 

Within the limits of the measurements, the results show unequivocally that the cobalt(II)/02 complex is serving as host for the organic guest molecule. The calculated distances between the center of electron spin density and the protons are shorter than in the cases where the electron is confined to a metal ion. This is expected since the O2 moiety resides between the metal ion site and the guest site. The limitations described advise against quantitative interpretation of the difference [53]. 

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