Complex zeolite-transition metal

Electronic properties of intrazeolitic complexes of transition metal ions with oxygen are of Interest for elucidation of oxygen binding and its activation for oxidation reactions. In an earlier study, dioxygen and monooxygen chromium species were reported to be formed by specific interactions between the oxygen molecules and the Cr ions planted in the Type A zeolite (1). 

Homoleptic phosphine complexes with transition metals, such as [Ni(PH3)4] or [Ni(PPh2H)4], have been prepared. " The main group Me3GaPH3 coordination compound can be pyrolyzed to afford GaP in Na+/H+ exchanged zeolite Y. ... 

The oxidative in-situ degradation of mono and polynuclear complexes of transition metals within the Y zeolite supercages has been employed to produce an array of oxide nanoclusters encapsulated in the intercrystalline voids of the matrix. The resulting materials were characterized by using a number of experimental techniques. The nanocomposites display extraordinary high activities in oxidation of CO and MeOH. 

Exchangeable cationic complexes are usually generated by in-situ complexation of transition metal ions. This process is obviously influenced by a variety of steric constraints. Occluded neutral species, either captured during synthesis or sorbed by the finished zeolite, may be subject to ligand substitution or react with structural (anionic or cationic) species. Complexes incorporated in framework sites have not been described so far their formation will obviously necessitate in most cases the breakage of T-O-M bonds, T and M being metal lattice sites. 

Similar films are obtained from powdered molecular sieves loaded with organic molecules Zeolite Y microparticles embedded into a polystyrene film and loaded with appropriately sized transition metal complexes allow selective electron exchange reactions between trapped and mobile species in the film... 

The important feature is the formation of a coordinatively unsaturated site (cus), permitting the reaction to occur in the coordinative sphere of the metal cation. The cus is a metal cationic site that is able to present at least three vacancies permitting, in the DeNOx process, to insert ligands such as NO, CO, H20, and any olefin or CxHyOz species that is able to behave like ligands in its coordinative environment. A cus can be located on kinks, ledges or corners of crystals [16] in such a location, they are unsaturated. This situation is quite comparable to an exchanged cation in a zeolite, as studied by Iizuka and Lundsford [17] or to a transition metal complex in solution, as studied by Hendriksen et al. [18] for NO reduction in the presence of CO. 

Extremely high ion exchange affinities are however sometimes observed for alkali metals (e.g. Cs) and transition metal ion complexes in clay minerals and zeolites. The objective of this paper is to give an account of the factors which are involved in these high selectivity phenomena. The discussion will be focussed mostly on montmorillonites and faujasites as representatives of the phyllosilicate and tectosilicate groups. 

Transition metal complexes encapsulated in the cavities of zeolites and meso-porous materials exhibit enhanced catalytic activity, compared to their neat analogs. " We had earlier found that Cu(II)-acetate exhibited enhanced regiose-lective orf/zo-hydroxylation of phenols using atmospheric oxygen as the oxidant on encapsulation in molecular sieves Y, MCM-22 or VPI-5. Rao et al. had also found a similar enhancement for encapsulation in Al-MCM-48. 

Other Compounds. Adsorption of MeNC into a cobalt(ii) zeolite at — 196"C was followed by e.s.r. spectroscopy, and the presence of low-spin [Co-(CNMe)j] and [Co(CNMe) ] complex cations demonstrated.This work represents one of the few successful attempts to produce well-characterized transition-metal complexes in a zeolite framework. Addition of NaCp to CoClj and [(BgC2H,Q)CoCp], previously reduced with sodium naphthalide gives a new bimetallic complex, for which structure (94) is proposed. ... 

Enantioselective hydrogenation over immobilised transition metal complex catalsyts, in 14th International Zeolite Conference, Cape Town, South Africa (eds E. van Steen, LH. Gallanan and M. Glaeys), The Gatalysis Society of South Africa, Gape Town, South Africa, pp. 975-7. 

From the previous paragraphes it follows that a substantial amount of experimental data exist that illustrate the oxygenation properties of zeolite catalysts. In very general terms zeolites are used to heterogenize transition metal ions in ion exchange or lattice positions, to stabilize transition metal oxide dispersions and to prepare ship-in-bottle complexes. 

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