Cobaltocene effects

Examples of preparation of copolymers are scarce. Mun et al. [81, 82] showed that the binary system of cobaltocene/ bis(ethylacetoacetato) copper (II) effectively initiates the living radical polymerizaton of MMA at 25 °C in acetonitrile. The polymerization activity of this initiator system was markedly affected by the solvent used. The synthesis of PMMA-b-PS copolymers with molecular weights reaching 700000 was successfully attempted by adding styrene to the living PMMA. The yield of the copolymers reached 80% when the MMA polymerization was carried out for three days. The same team [91] also synthesized PS-b-PMMA copolymers from the polymerization of MMA with polystyrene obtained in the presence of reduced nickel/halide systems. The yields range from 84 to 91% depending on the halide complex used. 

Metallocenes are useful electron donors as judged by their low (vertical) ionization potentials in the gas phase and oxidation potentials in solution (see Table 2). In fact, the electron-rich (19 e ) cobaltocene with an oxidation potential of E°ox = -0.9 V relative to the SCE [45] is commonly employed as a very powerful reducing agent in solution. Unlike the alkylmetals (vide supra), the HOMOs of metallocenes reside at the metal center [46] which accounts for two effects (i) Removal of an electron from the HOMO requires minimal reorganization energy which explains the facile oxidative conversion from metallocene to metallocenium. (ii) The metal-carbon bonding orbitals are little affected by the redox process, and thus the resulting metallocenium ions are very stable and can be isolated as salts. 

Fig. 7 Summary of the JT effect in cobaltocene. Symmetries of the corresponding geometries, electronic states and normal coordinates, numbering of C atoms in the cyclopentadienyl rings, as well as the relative energies of the different structures is given...

Table 6 Results of the DFT calculations performed to analyse the JT effect of cobaltocene energies (LDA) are given in eV the JT parameters Eyy and A are given in cm and Rjr in...

In this paper a new DFT based method for the qualitative and quantitative analysis of the adiabatic potential energy surfaces of JT active molecules is presented. It is shown how DFT can be successfully applied for the calculation of the JT parameters, and thus be a useful tool in understanding the JT effect and related phenomena. The performance of the model has been evaluated for tetrachlorovanadium(IV) (VCI4), an example of ideal, single mode problem cyclopentadienyl radical (C5H5) and bis(cyclopentadienyl)cobalt(II) (cobaltocene, CoCpi) as examples of the multimode problems. The JT parameters obtained using DFT are in excellent agreement with... 

Besides the substances mentioned so far, functionalized fuUerenes like the simple Bingel adduct can be intercalated into nanotubes as well (Section 2.5.5.2). The formation of peapods has further been described for metallocenes (e.g., ferrocene), porphyrines (e.g., erbium phthalocyanine complex) and small fragments of nanotubes. The most important prerequisite for the feasibility of inclusion is always a suitable proportion of sizes of both the tube and the structure to be embedded. For example, this effect can be observed for the intercalation of different cobaltocene derivatives into SWNT. The endohedral functionalization only takes place at an internal diameter of 0.92nm or above (Figure 3.100). But there is also an upper limit to successful incorporation. When the diameter of the nanotube is too large, the embedded species can easily diffuse away again from the host. Only few molecules are consequently found inside such a wide tube. 

An important finding was the discovery that intercalation of metallocenes into TaS2 produce a superconducting material with Tc = 3.2 K [329] and similar effects were observed by intercalation of cobaltocene into semiconducting SnSe2 (producing a material with = 8.3 K) [316, 319]. 

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