Aluminosilicates metal complexes

From the seminal work of Lunsford et al. in the early 1980s (DeWilde et al., 1980 Quayle and Lunsford, 1982), ship-in-a-bottle synthesis of metal complexes in the zeolite supercages, encapsulation of catalytically, optically, and/or electrochemically active species within micro- and mesoporous aluminosilicates, has received considerable attention (Alvaro et al., 2003). Site isolation of individual guest molecules, combined with shape and size restrictions imposed by the supercage steric limitations. 

Transition metal complexes of phthalocyanine encaged in faujasite type zeolites have been reported as efficient catalysts in the oxidation of alkanes at room temperature and atmospheric pressure [6-13]. These catalysts constitute potential inorganic mimics of remarkable enzymes such as monooxygenase cytochrome P-450 which displays the ultimate in substrate selectivity. In these enzymes the active site is the metal ion and the protein orientates the incoming substrate relative to the active metal center. Zeolites can be used as host lattices of metal complexes [14, 15]. The cavities of the aluminosilicate framework can replace the protein terciary structure of natural enzymes, thus sieving and orientating the substrate in its approach to the active site. Such catalysts are constructed by the so-called ship in a bottle synthesis the metal phthalocyanine complexes are synthesized in situ within the supercages of the zeolite... 

The results for the synthesis of an X type zeolite in the presence of FePc, CoPc, NiPc, and CuPc are shown in table 1. In all cases here the metal complex or metal complex solution was added to the aluminosilicate gel immediately after mixing the silicate and aluminate solutions. The mixture was magnetically stirred for 15 minutes before heating. The resulting crystals were washed with water extracted with pyridine and sublimed. The surface MPc complexes can not be removed by solvent extraction. However, vacuum sublimation appears to be completely effective for removing non-intrazeolite complexes. The product zeolites were various shades of blue but became a very pale blue-green after... 

On the other hand, if aluminosilicates are used as supports for chiral metal complex catalysts, they might reveal a contribution to asymmetric action as was found in the case of the hydrogenation catalyst [CoSalen] complex supported on hectorite... 

Aluminosilicate molecular sieves with the FAU structure have been crystallized in the presence of several metallophthalocyanines. A percentage of the complexes becomes included into the zeolites. The synthesis of NaX around the metal chelate represents a new method for encapsulating such complexes and modifying zeolite molecular sieves. The entrapped complexes were characterized by XRD, IR and UV-VIS spectroscopy. Preliminary results suggest the metal complexes may function as templates by modifying the gel chemistry. 

A considerable amount of research has been devoted to the study of zeolite-encapsulated metal complexes. Zeolites are crystalline aluminosilicates with typical pore diameters varying between 0.4 and 1.4nm. Due to the confined space of the zeolite cavity the selectivity is improved by diffusion. It has been found that the regioselectivities improve over those obtained with typical homogeneous catalysts but the activities are lower than in homogeneous systems. 

Adsorption of Metal Ions and Complexes on Aluminosilicate Minerals... 

In addition to stabilizing organic products by reaction with metal-exchanged clays, as indicated above, aluminosilicate minerals may enable the preparation of metal organic complexes that cannot be formed in solution. Thus a complex of Cu(II) with rubeanic acid (dithiooxamide) could be prepared by soaking Cu montmorillonite in an acetone solution of rubeanic acid (93). The intercalated complex was monomeric, aligned with Its molecular plane parallel to the interlamellar surfaces, and had a metal ligand ratio of 1 2 despite the tetradentate nature of the rubeanic acid. 

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