Transition metals, incorporation into

In general, the incorporation of an active transition metal catalyst into the anion of an ionic liquid appears to be an attractive concept for applications in which a high catalyst concentration is needed. 

In contrast to the ionic complexes of sodium, potassium, calcium, magnesium, barium, and cadmium, the ease with which transition metal complexes are formed (high constant of complex formation) can partly be attributed to the suitably sized atomic radii of the corresponding metals. Incorporated into the space provided by the comparatively rigid phthalocyanine ring, these metals fit best. An unfavorable volume ratio between the space within the phthalocyanine ring and the inserted metal, as is the case with the manganese complex, results in a low complex stability. 

Colored mixed-metal oxide pigments result from the incorporation of color-giving transition metal ions into an oxide host-lattice (see Table 5.9-13). Depending upon the particle size and properties of the chosen host, pigments (0.2 to 2 pm) or ceramic colorants (stains) (up to ca. 10 pm) result, which in many cases are characterized by high thermal and chemical stability and thus are suitable for the coloring of enamels and ceramics. 

While the incorporation of transition metal oxides into complexes with materials such as alumina can lower their volatilities by factors from 10 (CuO) to 1000 (BaO) depending primarily upon the heat of reaction between the two oxides, it is also likely that formation of very stable complex metal oxides, such as aluminates, can also greatiy lower the chemical activity of the transition metal. As mentioned above, Mn, Ni, and Co may requite stabilization in complex oxides for long catalyst life, but the complex oxides generally have inferior activity. The most active transition metal oxides (Ru and Cu) may still have unacceptable volatility as relatively active complex oxides. As a consequence, there may be a technology-limiting trade-off between the catalytic activity of metals and metal oxides and their chemical and thermal stability in combustion environments. 

Investigation of transition metal cations and their reactions fall in the realm of ESR spectroscopy. Such studies benefit by the high sensitivity of that spectroscopic technique. Moreover, ESR spectroscopy of cations in zeolites provides in many cases deeper insight into their coordination state. Thus, Clearfield et al. [4] were also the first to successfully apply ESR spectroscopy to prove the incorporation of transition metal cations into a zeolite structure by solid-solid interaction. In Figure 10, ESR spectra of Cu,Na-Y... 

The incorporation of transition-metal atoms into post-transition clusters may be a relatively new area of research, but the opposite process i.e. the incorporation of... 

The incorporation of anionic transition-metal complexes into PPy has enabled a range of spectroscopic techniques to be employed (UV-visible, EPR and Mossbauer spectroscopy) which have provided information about the counter-anion s structure and local environment. A relationship is apparent between the room-temperature conductivity and the position of the absorption maximum in the 300-500 nm region of the UV-visible spectrum. The conjugation length of the bipolarons seems to be an important factor that... 

PPy films containing transition-metal complexes should find applications in areas similar to those in which conventional PPy films are used [1]. In addition, the films discussed in this chapter may possess unique biosensing/chemical sensing properties. This area of research is being actively pursued at Monash University [101]. A different approach for the incorporation of transition-metal complexes into PPy, that has already received some attention [25,35], involves using chemically modified pyrrole monomers. This method should enable a wider range of transition-metal complexes to be incorporated into PPy than has been possible previously. 

In films intentionally doped with transition metals Shimizu et al. (1980c, 1981c) have observed ESR responses from Mn, Ni, and Fe. In all cases only a small fraction of the transition elements incorporated into the films contribute to the observed ESR, and details concerning the bonding of these elements in the films are presently very sketchy. 

Zeolites, i.e. microporous aluminosilicate materials with pores smaller than 2 nm, play key roles in the fields of sorption and catalysis [134, 135]. The global annual market for zeolites is several million tons. In the past few decades a large variety of zeolites and related zeotype materials have been produced, whereby transition metal incorporation is extensively used to modulate the catalytic characteristics of these materials. Since the catalytic properties depend on the structure and accessibility of the transition metal sites, a lot of effort is put into probing these sites. Nevertheless, the exact nature of the transition metal incorporation is often strongly debated, since most spectroscopic evidence for isomorphous substitution is indirect. 

In general, the incorporation of the active transition metal catalyst into the cation or anion of an ionic liquid appears to be an attractive concept for apphcations where a high catalyst concentration is needed. However, the physicochemical properties (in particular mdting point and viscosity) of such ionic liquids may be unfevorable in many cases if such an ionic liquid is used in neat form. 

The incorporation of transition metal ions into zeolites leads to interesting bifunctional catalysts in which metal and acid centers can act simultaneously. 

Similar to the IR investigations described, ESR measurements are carried out on mixtures of salt-zeolite or oxide-zeolite after ex-situ or in-situ heat treatment. Cells and procedures are the same as in other ESR studies of zeolite systems [26-27]. An advantage of ESR spectroscopy is its ability to provide information about the structural environment of the cations incorporated into the zeolite. ESR spectroscopy is a sensitive tool to check whether or not solid-state exchange of transition metal cations into zeolites was achieved. Quantitative determination of the degree of solid-state ion exchange is usually not very precise. Rather, rough estimations are derived from the spectra. Measurements reported were undertaken in X-band at room temperature, but also at elevated temperatures or the temperature of liquid nitrogen. 

Table 1.8 Rates of incorporation of some transition metal ions into tetrakis(N-methyl)tetraphenylporphyrin at 25 C in DMF solvent...

Transition metals can be incorporated into microporous or mesoporous materials by a postsynthetic ion-exchange treatment (impregnation) or by direct framework substitution by the addition of transition metal cations into the reaction mixture (110,111). 

Si02 — ZnO. Incorporation of transition metal ions into MgO increases base sites. The relation between the amount of base sites on metal cation-added MgO and ionic radii of the metal cations is shown in Fig. 3.45. Increase in base amount is prominent as the ionic radii of the metal cations are close to that of Mg. Metal ions whose ionic radii are close to that of Mg easily replace Mg in the MgO lattice. The replacement results in a deformed lattice and unbalanced electron charge distribution, increasing the basicity. 

There are essentially three ways in which polymers can be made electrically conducting via their own structures. These are via pyrolysis, doping and by producing an inherently conductive polymer structure such as via the incorporation of a transition metal atom into the polymer backbone. This chapter is principally devoted to conductive polymers of these types, but there is also another method of introducing conductivity to a polymer. In this method conductivity is achieved via the incorporation of conductive fillers. Although in this case the conductivity is not related to the chemistry of the polymer, but rather to the nature of the filler, these materials have been widely exploited commercially, and are thus worthy of inclusion in this chapter. 

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