Linear containing metals

Pyrazines and substituted pyrazines have long been known to act as exo-bidentate ligands to linearly bridge metal ions, and then have also been employed for the self-assembly of polymeric materials. With pyrazine (prz) varying the reaction conditions and stoichiometry, ID, 2D, and 3D structures containing silver(I) atoms with several coordination modes have been prepared.606-609 A 3D racemate is present in [Ag2(2,3-Me2prz)3](SbF6)2.610 A sawhorse connection has been achieved in the compound [Ag(N02)(pyz)] .611 With 2,2 -bipyrazine an infinite loop has been obtained.612... 

There also exist a variety of syntheses, stabilities, and characteristics, which are unique to each particular material. Further, macromolecules containing metal and metal-like elements can be produced in a variety of geometries, including linear, two-dimensional, three-dimensional, dendritic, and star arrays. 

In Scheme 1, octahedral coordination of central metals may lead to a three-dimensional polymer (22). In order to prevent the formation of this polymer and to prepare selectively a linear polymer, a special area for the reaction, such as the interspace of layer compounds or an organic monolayer film, is used. Kanda et al.19) synthesized the polymer in the organic monolayer film prepared by spreading a ligand solution on the surface of an aqueous solution containing metal ions. 

Retention of Rohrschneider-McReynolds standards of selected chiral alcohols and ketones was measured to determine the thermodynamic selectivity parameters of stationary phases containing (- -)-61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in poly(dimethylsiloxane) . Separation of selected racemic alcohols and ketones was achieved and the determined values of thermodynamic enantioselectivity were correlated with the molecular structure of the solutes studied. The decrease of the ionic radius of lanthanides induces greater increase of complexation efficiency for the alcohols than for the ketone coordination complexes. The selectivity of the studied stationary phases follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis acid-base interactions between the selected alcohols, ketones and lanthanide chelates. The retention of over fifty solutes on five stationary phases containing 61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in polydimethylsiloxane were later measured ". The initial motivation for this work was to explore the utility of a solvation parameter model proposed and developed by Abraham and coworkers for complexing stationary phases containing metal coordination centers. Linear solvation... 

The metal chelate polymers contain metal ions joined to one another by polyfunctional chelating agents. Examples are the linear polymers prepared from Schiff bases by mixing a solution of the base with a soluble metal salt. The insoluble polymer is precipitated (Marvel and Tarkoy, 1958) ... 

A variety of halide and haloamine complexes have been prepared which show evidence for one-dimensional structures in the solid state. The materials can be broken down into (1) complexes containing metals in the same oxidation state and (2) complexes comprised of metals in different oxidation states. Type (1) complexes may be dianions and dications, for example Magnus Green Salts or alternatively chains of neutral molecules, for example, Pt(en)Cl2. Type (2) complexes are comprised of alternating square planar rf metal complexes (metal = Pdii,Pt ,Aui i) and octahedral / metal complexes (metal = Pd, Pt ), or linear platinum complexes are formally trivalent while the gold complexes are formally divalent. 

Metal cluster complexes exhibit many interesting catalytic, optical, and other potentially useful properties for materials science applications, and many impressive advances have been made tvith respect to their synthesis [53-55]. The incorporation of these remarkable metal-containing units into the main chain of polymer structures clearly offers exciting possibilities [56], but this area is, in general, poorly developed. The follovring three examples of linear structures illustrate the growling interest and broad potential of this area. Dendritic structures that contain metal clusters are discussed in Chapter 8. 

To prepare polymers containing metals (e.g., Sn, Pb, Ni, Pd, Pt, or Ti) in the main chain, use is conunonly made of the linear condensation of metal dihalides and bifunctional Lewis bases [16], such as diols, diamines, dicarboxylic acids, hydrazines, oximes, and dithiols. The preparation of such metal-containing polymers can be represented in Scheme 10.1. 

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