Intercalation metal complexes

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

E. Comparison of Intercalated and Externally Bound Viologens as Quenchers of an Intercalated Metal Complex... 

Figure 20 Schematic of the doubly modified duplex showing the most probable (50%) separation of the intercalated metal complexes. (Reproduced by permission of Ref. 327)...

The iron catalyst can also be assembled in situ. The Na+ form of fluorotetrasilicic mica was ion exchanged with Fe +, then the iron-modified clay was treated with a solution of a bis(imino)pyridine ligand in l-butanol.i Formation of the intercalated metal complexes was inferred by the appearance of the characteristic u(C = N) mode at 1588cm i and an increase in the basal spacing of the clay from 1.0 to 1.6nm for XXIII and XXIV. The bulkier XXII apparently did not form due to the inability of the ligand to penetrate the interlayer space. 

Unal U, Matsumoto Y, Tanaka N, Kimura Y, Tamoto N (2003) Electrostatic self-assembly deposition of Titanate(IV) layered oxides intercalated with transition metal complexes and their electrochemical properties. J Phys Chem B 107 12680-12689... 

The catalytic application of clays is related closely to their swelling properties. Appropriate swelling enables the reactant to enter the interlamellar region. The ion exchange is usually performed in aquatic media because the swelling of clays in organic solvents, and thus the expansion of the interlayer space, is limited and it makes it difficult for a bulky metal complex to penetrate between the layers. Nonaqueous intercalation of montmorillonite with a water-sensitive multinuclear manganese complex was achieved, however, with the use of nitromethane as solvent.139 The complex cation is intercalated parallel to the sheets. 

When supported complexes are the catalysts, two types of ionic solid were used zeolites and clays. The structures of these solids (microporous and lamellar respectively) help to improve the stability of the complex catalyst under the reaction conditions by preventing the catalytic species from undergoing dimerization or aggregation, both phenomena which are known to be deactivating. In some cases, the pore walls can tune the selectivity of the reaction by steric effects. The strong similarities of zeolites with the protein portion of natural enzymes was emphasized by Herron.20 The protein protects the active site from side reactions, sieves the substrate molecules, and provides a stereochemically demanding void. Metal complexes have been encapsulated in zeolites, successfully mimicking metalloenzymes for oxidation reactions. Two methods of synthesis of such encapsulated/intercalated complexes have been tested, as follows. 

Being thermally decomposed onto the surface of carbon, this complex is expected to form very small catalytically active NiCo204 spinel centers. Thus, we have studied the catalytic activity of the products of pyrolysis at different temperatures toward two electrochemical reactions -reduction of oxygen in alkaline electrolyte and intercalation of lithium into carbons in aprotic electrolyte of Li-ion battery. To our knowledge, the catalytic effect of the metal complexes in the second reaction was not yet considered in the literature. 

The most significant class of inorganic supports, which is used for the direct ion exchange of positively charged transition-metal complexes, are smectite clays. Pin-navaia has introduced the use of these swelling, layered silicate clays for catalysis. Other clays include montmorillonite, bentonite, and laponite. As shown by Pinna-vaia, cationic transition-metal complexes can be readily exchanged (intercalated) into the solvated interlayers of these silicates (Eq. (1)) [117] ... 

When using appropriate solvents for swelling of the interlayers, the intercalated metal ions are accessible to both substrates and catalysis. One of the first such demonstrations was also carried out with the Wilkinson complex for hydrogena-... 

The methods giving access to the effects of interacting molecules on the physical properties of DNA are cited first because they are considered as the most classical ones for testing intercalation, although in the particular case of the metallic complexes developed below, they have bren generally less applied than the spectroscopic techniques. 

In the example in Figure 2.24, a clay (a layered double hydroxide [LDH]) was intercalated with a transition metal complex (NH4)2MnBr4. The EXAFS data in Figure 2.24(a) shows the Mn K-edge EXAFS of the pure complex, and we see one coordination sphere of four Br atoms at a distance of 2.49 A, corresponding well to the tetrahedral coordination found in the X-ray crystal structure. However, after intercalation, the complex reacts with the layers in the clay, and the coordination changes to distorted octahedral where Mn is now surrounded by four 0 atoms at a distance of 1.92 A and two Br atoms at a distance of 2.25 A. 

Heavier metal ions and metal complexes can find sites on nitrogen atoms of the nucleic acid bases. Examples are the platinum complex cisplatin and the DNA-cleaving antibiotic neocarzinostatin (Box 5-B). Can metals interact with the n electrons of stacked DNA bases A surprising result has been reported for intercalating complexes of ruthenium (Ru) and rhodium (Rh). Apparent transfer of electrons between Ru (II) and Rh (III) over distances in excess of 4.0 nm, presumably through the stacked bases, has been observed,181 as has electron transfer from other ions.181a Stacked bases are apparently semiconductors.182... 

The reported strategies utilized in DNA sensing include (1) sequence-specific hybridization processes based on the oxidation signal of most electroactive DNA bases, guanine and adenine [13,24] or (2) quasi-specific detection of small molecules capable of binding by intercalation or complexation with DNA, such as metal coordination complexes, antibiotics, pesticides, pollutants, etc. [17,18] or in the presence of some metal tags such as gold, silver nanoparticles, etc. [23,50,51]. 

Due to their high charge density [44,47], a high degree of anion exchange (80-100%) can be readily achieved [48], Like the ZrPs, they are also thermally stable. The intercalation compounds of LDH are found to have potential importance as catalysts, ion exchangers, ceramic precursors, antacid drugs, and as hosts for anionic dyes and metal complexes [49],... 

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