Encapsulation of Metal Complexes

Vancaeyzeele et al. [70] encapsulated unsymmetrical lanthanide-P-diketonato [lanthanide tris(4,4,4-trifluoro-l-(2-naphthyl-1,3-butanedione)] complexes (Pr, Ho, La, Tb, Eu) in crosslinked polystyrene nanoparticles. They found that the entire amount of the complex is encapsulated in the nanoparticle. Both single element and multi-element particles of different sizes were obtained. The lanthanide content of the particles was determined by inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (ICP-OES). The particles were used to quantify the amount of differently sized element-encoded particles in different, clinically relevant cell lines. 

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Layered inorganic solids have been used for site isolation, for example, nickel phosphine complexes confined within the interlayer spaces of sepiolite have been used as olefin hydrogenation catalysts [63], and similarly there has been the encapsulation of metal complexes into zirconium phosphates [64], The principal idea is illustrated in Figure 5.8. The metal complex can be encapsulated by covalent means (a) or by non-covalent interactions (b). 

A Ni(salen) complex [salen = bis(salicylidene)ethylenediamine] encapsulated in zeolite is highly efficient in the hydrogenation of simple alkenes (cyclohexene, cyclooctene, 1-hexene).451 This method, which is the encapsulation of metal complexes into the cavities of zeolites, offers the unique possibility of shape-selective... 

Based on host-guest interaction, microporous zeolites have been used as heterogeneous host for encapsulation of metal complexes and organometallic fragments. For zeolite-encapsulated photosensitizer, the steric and electrostatic constraint imposed on the complexes within the channels or cages of zeolites can alter the photochemical and photophysical properties of the guest complexes and diminish the photodegradation and undesirable electron transfer reactions [6]. But, the pore sizes (-13 A) of microporous zeolites are too small for... 

Due to the nature of carbon materials, the presentation of representative methods for surface derivatization will follow an approach different from that described in the preceding section, which is based on the spatial target site where physical-chemical modification can take place (1) immobilization performed at edges and/or ends and defects of graphitic sheets, (2) immobilization onto the graphene sheets, and (3) exclusively for CNTs we present some examples of endohedral encapsulation of metal complexes. For the first two cases, covalent bonding and noncovalent interactions can occur directly between the transition metal complex and carbon supports or via spacers grafted to the carbon surface. 

Encapsulation of Metal Complexes The nanostructure of CNTs (typical diameters range from 0.7 to 2.0 mn for SWCNTs) enables the endohedral encapsulation of molecules [14,15,21,31b,38]. It is possible to encapsulate molecules inside the tubes as long as the size of the molecules is smaller than the nanotubes and have enough kinetic energy to enter the open ends of CNTs. Practically, all organic solvents have a surface tension that makes possible the insertion of molecnles into the CNT internal diameters. 

The attachment and encapsulation of metals and metal complexes in the cavities of zeolites is an active area of research and provides a versatile method for the modification of these molecular sieves (39). Because of the enforced dispersion of the metal complexes in the zeolite, systems not readily observable in solution can be investigated in zeolites. For example, the mononuclear superoxo adduct of the cobalt(HI)-ammine system, [Co(NH3 )6(00-)]2+, which would be expected to dimerize in solution, could be observed entrapped in zeolite Y (40). 

Transition metal complexes encapsulated in the channel of zeolites have received a lot of attention, due to their high catalytic activity, selectivity and stability in field of oxidation reactions. Generally, transition metal complex have only been immobilized in the classical large porous zeolites, such as X, Y[l-4], But the restricted sizes of the pores and cavities of the zeolites not only limit the maximum size of the complex which can be accommodated, but also impose resistance on the diffusion of substrates and products. Mesoporous molecular sieves, due to their high surface area and ordered pore structure, offer the potentiality as a good host for immobilizing transition complexes[5-7]. The previous reports are mainly about molecular sieves encapsulated mononuclear metal complex, whereas the reports about immobilization of heteronuclear metal complex in the host material are few. Here, we try to prepare MCM-41 loaded with binuclear Co(II)-La(III) complex with bis-salicylaldehyde ethylenediamine schiff base. 

Replacement of the hydrogen bonds in oxime complexes with boron bridges leads to macrocyclic complexes such as those from dimethyl glyoxime (equation 59).201,202 This kinetic template technique has been used for the encapsulation of metals inside cage ligands.203 204... 

Incarceration of metals varying from potassium to heavy atoms such as lanthanum or uranium within the fullerenes have given new classes of metalloful-lerenes. These materials clearly demonstrate the exoskeleton required for these encapsulations [48a, b]. Conversely metals may also be attached to the exterior of the fullerene cage [48c] to give a distinctly different class of metal complexes. 

Figure 2 Biomimetic synthesis strategy for peptide encapsulated nanoclusters. Synthesis begins with complexation of peptide hgand to metal ion, followed by borohydride reduction of metal complex, nucleation, and formation of peptide stabilized nanocluster. (Reprinted with permission from Ref. 1. 2003 American Chemical Society)...

Biomimetic Synthesis of Nanoparticles Carbonyl Complexes of the Transition Metals Metallic Materials Deposition Metal-organic Precursors Polynuclear Organometallic Cluster Complexes Porous Inorganic Materials Self-assembled Inorganic Architectures Semiconductor Nanocrystal Quantum Dots Sol-Gel Encapsulation of Metal and Semiconductor Nanocrystals. 

The capture of metal complexes is achieved in the synthesis of clusters within the porous network of zeolites, where the reactants are small enough to enter the large cavities, but the clusters formed are too large to escape ( ship- in-the-bottle synthesis). The cages limit the size of the cluster compounds that can be formed and the entrance to the porous channels prevents the departure from the cages. Other methods of encapsulating metal complexes utilize polymerization or polycondensation reactions such as the sol-gel process. The metal complex is dissolved in the medium to be polymerized and is therefore trapped in the matrix formed [93] (cf. Section 3.2.2). The limitations clearly arise from the porosity of the polymer formed. A pore structure with pores that are too wide cannot prevent the leaching of the complex, whereas a pore diameter that is too small results in mass-transfer limitations. 

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. 

UV spectra used for a semi-quantitive determination of the amount of intracrystalline phthalocyanine complexes were taken on a Perkin Elmer UV-visible spectrophotometer. A calibration curve was obtained by dissolving known amounts of metal complex in concentrated sulfuric acid. Zeolite was added to take into account matrix effects. Surface area and pore volume measurements were performed on a Micromeritics ASAP 2000 by absorption of nitrogen gas at liquid nitrogen temperature. X-ray powder diffraction of the zeolites was used to ensure good crystallinity after the exchange and encapsulation procedures... 

In comparison to the zeolite synthesis approach there are many disadvantages associated with the preparation of intrazeolite complexes by the flexible ligand and template synthesis methods. The complexes are difficult to characterize, especially if the ligand has multiple coordination modes available and some of the target metal ions may remain uncomplexed which will complicate any reactivity studies. Additionally, there are limitations to the types of metal complexes that might be encapsulated in a zeolite. The only criteria for incorporating metal complexes... 

The crystallization of zeolites and molecular sieves with metal complexes represents a fresh strategy for the synthesis of these materials as well as a novel method for encapsulation of metal chelate complexes. We have shown that several first row tranistion metal phthalocyanines complexes can be encapsulated in X and A type zeolites by synthesizing the zeolite around the metal complex. Preliminary results indicate the concentration and type of phthalocyanine complex modify the crystallization of X type zeolites. The extension of this method to other metal chelate complexes and molecular sieves is currently under investigation. 

Therefore, the encapsulation methodology is that which can better mimic the catalytic behavior of metal complexes in the homogeneous phase. This methodology depends on the respective sizes of the complex and the cavity where the complex should be entrapped. To prevent the leaching of the complex after encapsulation, the size of the complex has to be bigger than the dimensions of the cavity, which is the most important limitation of this method. As in covalent... 

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