Coordination polymers oxidative stability

Bailar listed a number of principles that can be considered in designing coordination polymers as follows (1) Little flexibility is imparted by the metal ion or within its immediate environment thus, flexibility must arise from the organic moiety. Flexibility increases as the covalent nature of metal-ligand bond increases. (2) Metal ions only stabilize ligands in their immediate vicinity thus, the chelates should be strong and close to the metal ions. (3) Thermal, oxidative, and hydrolytic stabilities are not directly related polymers must be designed specifically for the properties desired. (4) Metal-ligand bonds have sufficient ionic character... 

The work described here supports the view that the chemical combination of metal ions with organic molecules leads to coordination complexes and polymers with enhanced stability with respect to weight loss, thermal degradation, or oxidation. Bis(8-hydroxyquinoline) derivatives were used to prepare a series of coordination polymers containing first-row transition metals, and the thermal stabilities of the polymers were evaluated. The influence of the structure of the organic molecule and the role of the metal are discussed. 

The coordination polymers of 8-hydroxyquinoline derivatives are not only stabilized with respect to temperature, but a preliminary study (24) has disclosed that these polymers are also highly resistant to thermal oxidation. When samples were heated at 190 °C. in a sealed system in an air atmosphere, very little oxidation occurred, even after several days,... 

Coordination polymers of Zn(II) derived from bisthiopicolinamides show the best thermal stabilities and can be heated at 300°C for 6 h without changed The Zn(II) derivatives of bissalicaldimines also show the best thermal stability. The often found superior thermal stability of Zn(II) derivatives arise from its single oxidation state. Transition metals can be oxidized to higher states, catalyzing the decomposition of the polymer chains. 

Nitrogen-based radicals like nitroxides and verdazyl derivatives fulfill the basic requirements, since they share high stability and persistency and can be functionalized to coordinate metal ions. Charged radicals such as tetracyanoeth-ylene [68, 69] and tetracyanoquinone radical anions have also been reported [70], and a special case is represented by the o-quinone ligands that can be found in different oxidation states in valence tautomeric compounds [71]. Recently, PTM radicals substituted with carboxylate groups have been used to obtain metal-radical coordination polymers, which, in some cases, exhibit porous structures and relevant magnetic properties. Example of such porous magnets will be reported in detail in Section 4.3.3 [72]. 

The thermostable luminophores composed of Eu(III) coordination polymers were successfully synthesized (Fig. 2.10). In particular, [Eu(hfa)3(dppcz)] exhibits both high emission quantum yields (thermal stability (decomposition point =300 °C) due to a tight-binding structure composed of Eu(III) ions and low-vibrational phosphine oxide, although many types of... 

In Chap. 2, novel thermostable luminophores comprised of Eu(ni) coordination polymers [Eu(hfa)3(dpb)] , [Eu(hfa)3(dpbp)] , and [Eu(hfa)3(dppcz)] were successfully synthesized. In particular, [Eu(hfa)3(dppcz)] exhibited both high emission quantum yields (< Ln = 83 %) and remarkable thermal stability (decomposition point = 300 °C) due to a tight-binding stmcture composed of Eu(III) ions and low-vibrational phosphine oxide, although many types of luminescent organic dyes are generally decomposed at temperatures under 200 °C. The emission quantum yields of these coordination polymers are similar to those of strong-luminescent coordination polymers in former chapters. These coordination polymers are expected to employ in optics applications such as luminescent plastics, displays, and opto-electronic devices. 

Phosphine complexes, osmium, 19 642 Phosphine coordination complexes, of uranium, 25 436 Phosphine derivatives, 19 28 Phosphine oxide(s), 11 495-496 19 66 predicted deviations from Raoult s law based on hydrogen-bonding interactions, 8 814t in salicylic acid manufacture, 22 8 Phosphine oxide diols/triols, 11 501 Phosphine selenides, 22 90 Phosphinic acid, 19 20, 54-55 Phosphinic anhydride, 11 499 Phosphinothricin acetyltransferase (PAT) proteins, 13 360 Phosphite esters, 19 20 Phosphites, in VDC polymer stabilization, 25 720... 

A material with nitrogen-coordinated Ru was obtained from a silica-linked 2-(phenylazo)pyridine ligand. Results for cyclobutanol oxidation with 02 and the sacrificial oxidant isobutyraldehyde indicate that one- and two-electron oxidations occur simultaneously. The stability of the catalyst is not always guaranteed, probably because acids may be formed in oxidations of alcohols (284). Leaching problems are also encountered with a polymer-bound Ru Schiff base complex, used in oxidation of benzyl alcohol (285). 

It was discovered that the addition of 1,3-cyclohexadiene to the Rh -catalyzed reactions increased the rate of butadiene polymerization by a factor of over 20 [20]. Considering the reducing properties of 1,3-cyclohexadiene, this effect could be due to the reduction of Rh to Rh and stabilization of this low oxidation state by the diene ligands. With neat 1,3-cyclohexadiene, Rh is reduced to the metallic state. These emulsion polymerizations are sensitive to the presence of Lewis basic functional groups. A stoichiometric amount of amine (based on Rh) is sufficient to inhibit polymerization completely. It was also discovered that styrene could be polymerized using the Rh catalyst. However, the atactic nature of the polymer, along with the kinetic behavior of the reaction, indicated that a free-radical process, rather than a coordination-insertion mechanism, was operative. 

Other reference electrodes have been proposed for use in the nonaqueous solvents that are widely used in coordination chemistry. Their main advantage is that they allow one to work with a single solvent. Among these electrodes, the Ag+/Ag electrode is reversible in many solvents.4 Ag+ ions are introduced as salts, such as AgCl or AgBF4. However, the inner solution has to be refreshed due to the reactivity of Ag+. Another class consists of redox electrodes in which the two components are in solution, such as ferrocenium ion/ferrocene Fc+/Fc.5 Since the potential is dependent on the concentration ratio of the redox couple, this ratio must be kept constant. An attractive solution to prevent the use of a junction lies in the preparation of a functionalized-polymer coated electrode such as poly(vinylferrocene).6 The polymer is deposited by electrooxidation in its oxidized form, polyFc+, and then partially reduced to yield poly Fc+/Fc. Their use is limited by their relative stability in the different solvents. 

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