Backbone structure transition metals coordination

The sensor covalently joined a bithiophene unit with a crown ether macrocycle as the monomeric unit for polymerization (Scheme 1). The spatial distribution of oxygen coordination sites around a metal ion causes planarization of the backbone in the bithiophene, eliciting a red-shift upon metal coordination. They expanded upon this bithiophene structure by replacing the crown ether macrocycle with a calixarene-based ion receptor, and worked with both a monomeric model and a polymeric version to compare ion-binding specificity and behavior [13]. The monomer exhibited less specificity for Na+ than the polymer. However, with the gradual addition of Na+, the monomer underwent a steady blue shift in fluorescence emission whereas the polymer appeared to reach a critical concentration where the spectra rapidly transitioned to a shorter wavelength. Scheme 2 illustrates the proposed explanation for blue shift with increasing ion concentration. 

Many of these systems employ charged polymers or polyelectrolytes that confer on them particular properties due to the existence of electrical charges in the polymer structure. Oyama and Anson [14,15] introduced polyelectrolytes at electrode surfaces by using poly(vinylpiridine), PVP, and poly-(acrylonitrile) to coordinate metal complexes via the pyridines or nitrile groups pending from the polymer backbone. Thomas Meyer s group at North Carolina [16, 17[ also employed poly(vinylpyridine) to coordinate Ru, Os, Re and other transition-metal complexes by generating an open coordination site on the precursor-metal complex. 

Phthalazines are commonly used as ligands in transition metal cataysis since the structure provides a planar backbone with coordinating nitrogens. One of the most prevalent phthalazine-based ligands is known as (DHQD)2PHAL (154) <94CR2483>. A recent example of the use of 154 was in the catalytic asymmetric dihydroxylation by osmium tetroxide with air as the ultimate oxidant reported by Krief and co-worker <99TL4189>. 

It is our aim to combine the outstanding properties of nano- microtubes and metal-doped silica gel. There are many kinds of dopands, e.g., transition metal and rare-earth ions. A further advantage is the high heat resistance of these tubular structures up to 250 °C with organically functionalization, and up to 800 °C with only metal functionalization. Metal ions can be built directly in the silica backbone or adsorbed on the surface. Functionalized silanes can also be used to coordinate metal ions and build them into the tubes. 

Diimine-based ligands such as bipyridine have been used widely as ligands for transition metals. Their conjugated structure makes them attractive candidates for incorporation directly into a conjugated polymer backbone. In this configuration, metal centers that are coordinated by the diimine are strongly electronically coupled to the polymer. 

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