Metal guest

The formation of complexes of non-metallic guests by crowns as well as by other types of cyclic hosts is discussed in Chapter 5. 

This chapter has largely been concerned with two- and three-dimensional polyether ligand systems and their complexes with a range of metal ions. A variety of other related ligand systems are also known but in many instances these have been primarily used to form complexes with non-metallic guests. 

The formation and properties of a range of host-guest complexes involving macrocyclic hosts and non-metallic guests are described in the next chapter. 

Host-guest chemistry macrocyclic hosts and non-metallic guests... 

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,... 

Metal loading studies of this type serve to enlighten the factors which control the impregnation of organometallics into zeolites, as well as providing an indirect probe of internal versus external location of the metal guests. In the following, a direct spectroscopic probe of this kind of process is presented. 

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. 

The choice of (n5-C5H5) 2Cr as an epr spin probe in these applications, offers numerous opportunities for investigating the ultimate form and location of thg metal guest. Its molecular dimensions are estimated to be 4.34A x 4.44A (26) and so it should be a useful can-... 

Overall it is quite clear, that a combination of epr spin-probes, UV-vis reflectance spectroscopy, size exclusion and intrazeolite oxidation experiments are able to effectively differentiate those organometallic-zeolite impregnations which place metal guests within the internal voids of the zeolite compared to those on the external surface of the zeolite lattice. 

This paper describes some new zeolite organometallic impregnation experiments, in which a combination of metal loading, size exclusion, intrazeolite chemistry and diffusion considerations in conjunction with epr, far-IR and UV-visible reflectance spectroscopic probes, serve to distinguish metal guests located in the intracrystalline voids of the zeolite from those located on the external surface. 

D. Electrochemical Recognition of Transition Metal Guest Cations by Ferrocene Aza-, Thia-Donor Macrocyclic Ligands... 

Besides the ferrocene crown ether ligands described earlier, a variety of related macrocyclic ferrocenophanes containing various sulfur, oxygen, and nitrogen heteroatoms have been reported by a number of groups (110-115) (Scheme 21). These ligands complex transition metal guest cations such as Ag(I), Cu(I), and Pd(II) (116,117). Of particular... 

Gokel for reducible quinone (25, 26) and nitroaromatic (32, 33) lariat crown ethers with alkali metal guest cations discussed earlier. Support for the latter effect comes from the related ligand system (81), containing no amide carbonyl groups, and electrochemical results revealing... 

Figure 3. Three basic strategies for the incorporation of multiply bonded metal-metal guest species into vanadyl and zirconium phosphate host layers, (a) The direct intercalation of solvated M—— M cores into the native layered phosphate host structure, (b) Incorporation of M—— M complexes with ancillary ligands containing a Lewis basic site, (c) Coordination of M—— M cores with ligands provided from modified phosphate layers.

The results of this study suggest that silver atom and cluster optical absorption and fluorescent probes offer a very sensitive method for assessing the strength of a metal support interaction and a way of monitoring subtle alterations in electronic charge density at the trapping site of a metal guest. 

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