Metal-polymer complexes, structure

Computationally, a large part of the work related to the subject of this book has involved determination of equilibrium geometries of metal-polymer complexes and the relation between geometrical and electronic structure. Since there is a lack of experimental information concerning equilibrium geometries, these data are only accessible via calculations in which the total energy is minimized with respect to the positions of the nuclei. 

Metal-containing polymers may be produced by various methods, such as chemical reactions of precursors— in particular, reactions of metal salts in polymer solutions, the treatment of polymers with metal vapors, or the polymerization of various metal-monomer systems [1-4], Depending on the metal nature and the polymer structure, these processes lead to organometallic units incorporated into polymer chains, metal-polymer complexes, or metal clusters and nanoparticles physically connected with polymer matrix. Of special interest are syntheses with the use of metal vapors. In this case, metal atoms or clusters are not protected by complexones or solvate envelopes and consequently have specific high reactivity. It should be noted that the apparatus and principles of metal vapor synthesis techniques are closely related to many industrial processes with participation of atomic and molecular species [5]—for example, manufacturing devices for microelectronic from different metals and metal containing precursors [6]. Vapor synthesis methods employ varying metals and... 

STRUCTURE OF CRYOCHEMICALLY SYNTHESIZED METAL-POLYMER COMPLEXES... 

Depending on the metal nature and monomer structure, the vapor deposition cryopolymerization of metal-monomer systems yields a possibility producing metal-containing polymers of different structure. Polymer containing organo-metallic groups or metal-polymer complexes can be prepared using pre-... 

As can be seen from the discussion above, the polyelectrolyte gel-surfactant complexes present interesting hybrid metal-polymer nanocomposites, allowing a vast variety of incorporated metals and metal-polymer-surfactant structures. The limitations of these systems are their heterogeneous character (insoluble in any media) and excessive sensitivity to external parameters (pH, temperature, etc.). 

Metal ion complexation affects the structure and physicochemical properties of polymer ligands, and this is generally observed in metal-polymer complexes, for example, Li-polymer complexes (electrolytes). 

As we saw in the first chapter, polymers have become important engineering materials. They are much more complex structurally than metals, and because of this they have very special mechanical properties. The extreme elasticity of a rubber band is one the formability of polyethylene is another. 

Metal-acetylide complexes including metal-poly(yne) polymers often show unique properties [21-23]. Thus, metal-acetylide dendrimers are of interest because amplification of the functionality due to metal-acetylide units based on three-dimensional assembly with a regular dendritic structure is expected. 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

Crosslinked polymer particles with a rather complex structure, which have also been designated by the name microgels and recommended as components of metal effect paints, consist of carboxyl-terminated oligoesters of 12-hydroxy stearic acid which were reacted with glycidyl methacrylate, subsequently copolymerized with MMA and hydroxymethyl methacrylate and then crosslinked by hydroxy melamine [346]. 

Molecular catalysts, often in the form of metal ions complexed to a suitable ligand, can also be attached to dendrimer surfaces [3,9,10,93,94,96,148,149]. Such materials are generally structurally better defined than catalysts bounded to linear polymers, but like random-polymer catalysts they can be easily separated from reaction products. Note, however, that this approach results in a synthetic dead-end as far as further manipulation of the terminal groups is concerned, and thus some of the advantages of using dendrimers, such as solubility modulation, are lost. 

In this review, well-defined metal-containing PAEs are described whose primary structure is represented by one of the schematic drawings A-C and E shown in Fig. 2. In contrast to the structures shown in the A-C systems, E has a conjugated phenyleneethynylene with metal chelates as end groups. PAEs containing metal complex as side groups (D) have, up to now, not been described in the literature. The classes of compounds such as metal-bridged alkynes, the poly(metallayne)s, and polymer carbyne complexes (structures G and H) do not in fact represent PAEs. 

This article deals with the polymer-metal complexes (Schemes 1 —5), because they have the following merits in comparison with other polymeric metal complexes, (i) Metal ion and ligand site can be chosen for study without restrictions, (ii) It is not difficult to control the molecular weight of a polymer complex and to modify the structure of a polymer ligand, (iii) The polymer complex is soluble in both aqueous and nonaqueous solvent, (iv) It is possible to change the ratio of the organic polymer part to the inorganic metal complex part. This explains why the polymer often affects the behavior of the metal complex. 

A Co(IH) complex is inert in ligand-substitution reactions, and its uniform structure is thus maintained even in an aqueous solution. The reaction mechanism of a Co(III) complex in solution is well known, so that a pendant-type polymer-Co(IU) complex, e.g. 17,19, is one of the most suitable compounds for a quantitative study of the effects of a polymer ligand on the reactivity of a metal complex. The reactivities of the polymer-Co(III) complexes are discussed here kinetically and compared with those of the monomeric Co(III) complexes in the following reactions electron-transfer reactions between the polymer complexes and Fe(II) [Eqs. (5) and (6)], and the ligand-substitution reaction of the polymer-Co(III) complex with hydroxy ions or water [Eqs. (7) and (8)J. One of the electron-transfer reactions proceeds via... 

The theory of electron transfer in chemical and biological systems has been discussed by Marcus and many other workers 74 84). Recently, Larson 8l) has discussed the theory of electron transfer in protein and polymer-metal complex structures on the basis of a model first proposed by Marcus. In biological systems, electrons are mediated between redox centers over large distances (1.5 to 3.0 nm). Under non-adiabatic conditions, as the two energy surfaces have little interaction (Fig. 5), the electron transfer reaction does not occur. If there is weak interaction between the two surfaces, a, and a2, the system tends to split into two continuous energy surfaces, A3 and A2, with a small gap A which corresponds to the electronic coupling matrix element. Under such conditions, electron transfer from reductant to oxidant may occur, with the probability (x) given by Eq. (10),... 

In the most important series of polymers of this type, the metallotetraphenylporphyrins, a metalloporphyrin ring bears four substituted phenylene groups X, as is shown in 7.19. The metals M in the structure are typically iron, cobalt, or nickel cations, and the substituents on the phenylene groups include -NH2, -NR2, and -OH. These polymers are generally insoluble. Some have been prepared by electro-oxidative polymerizations in the form of electroactive films on electrode surfaces.79 The cobalt-metallated polymer is of particular interest since it is an electrocatalyst for the reduction of dioxygen. Films of poly(trisbipyridine)-metal complexes also have interesting electrochemical properties, in particular electrochromism and electrical conductivity.78 The closely related polymer, poly(2-vinylpyridine), also forms metal complexes, for example with copper(II) chloride.80... 

The importance of the interaction with photons in the natural world can hardly be overstated. It forms the basis for photosynthesis converting carbon dioxide and water into more complex plant-associated structures. This is effectively accomplished employing chlorophyll as the catalytic site (this topic will be dealt with more fully later in the chapter). Chlorophyll contains a metal atom within a polymeric matrix, so it illustrates the importance of such metal-polymer combinations. T oday, with the rebirth of green materials and green chemistry use of clean fuel—namely, sunlight—is increasing in both interest and understanding. 

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