Thin films coordination polymers

Under current investigation are the synthesis and properties of multimetallic thin films containing Ru, Os1, and Re1 in a wide variety of coordination environments. Judicious choice of such materials may lead to creation of an electroactive polymer film which would exhibit a bandlike spectrum of reversible, metal-centered redox processes extending from ca. -0.6 to +1.5 V. 

Porous materials discussed at the International Conference on Materials for Advanced Technologies 2005 included clay minerals, silicates, aluminosilicates, organosilicas, metals, silicon, metal oxides, carbons and carbon nanotubes, polymers and coordination polymers, or metal-organic frameworks (MOFs), metal and metal oxide nanoparticles, thin films, membranes, and monoliths (Zhao, 2006). 

Hoffman and co-workers have carried out a series of studies on the passive films on iron, with particular attention to cell design. They have employed a so-called bag cell that allows for the in-situ passivation or cathodic protection of the iron films which were deposited onto gold films deposited on melinex (polymer film with excellent adhesive properties). In addition, they employed a setup in which the working electrode is partially immersed in solution and continuously rotated. In this way, they could expose the electrode to the x-ray beam with ostensibly only a very thin film of electrolyte. Under these conditions, they were able to obtain spectra of the film as prepared, a cathodically protected film as well as a film passivated in borate solution at 1.3 V. From an analysis of their data, they concluded that the passive film had an Fe—O coordination with 6 near neighbors at a distance of 2 + 0.1 A. The approach followed by these authors appears most appropriate since they were able to reduce the deposited films... 

In the second approach, metal-ion/complex was first attached to one of the polymer blocks. A thin film of the resulting polymer metal complex was then obtained by spin coating/solution casting. Alternatively, the polymer metal complex may also be dissolved in a suitable solvent system that selectively dissolves one of the blocks. Micelles or nanosized aggregates formed in this case. The micellization of amphiphilic block copolymers and their use in the formation of metal nanoparticles has been discussed previously.44 A monolayer of micelles was introduced on a substrate surface by dipping or electrostatic attraction. The substrate was then subjected to further chemical or physical treatments as mentioned earlier. The third approach involves the formation of micelles from the metal-free block copolymer in a suitable solvent system. The micelle solution was then added with metal ion, which was selectively coordinated to one of the blocks. These micelle-metal complexes can also be processed by a procedures similar to the second approach. 

An example of this approach is represented by the growth of 3-D coordination polymers with SCO properties via stepwise adsorption reactions for multilayer films based entirely on intra- and interlayer coordination bonds Fe(pyrazine) [Pt(CN) ] [218, 219], Indeed, after functionalization of the surface with the appropriate anchoring layer the coordination polymer is built in a stepwise fashion, alternating the metal ion (Fe "), the platinum salt ([Pt(CN) ] ), and pyrazine. The polymer shows many interesting properties, with the SCO transition accompanied by a variation in the dielectric constant of the material accompanied by a room temperature hysteresis of the dielectric constants. This dielectric hysteretic property may be useful in building molecular memory devices that can store information by high- and low-capacitance states. What must be remarked here is that these appealing properties cannot be exploited in bulk materials, but only in thin films. 

J.H. Jang and W. L. Mattice, The effect of solid wall interactions on an amorphous polyethylene thin film, using a Monte Carlo simulation on a high coordination lattice. Polymer 40 4685 (1999). 

The choice of the particular monomers is based on the fact that PI is a nonpolar low Tg polymer, P2VP is a relatively more polar material with a coordinating ability, due to the presence of nitrogen in the side phenyl ring, with high Tg and the potential to be transformed into a water-soluble polyelectrolyte by postpolymerization reaction. On the other hand, PEO is a semicrystalline polymer, water-soluble (polar), and biocompatible. The incorporation of all these diverse properties in the same molecule makes these materials very interesting in terms of their self-organization in solution, bulk, and thin films. 

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