Cobalt charge transfer processes

An iron-promoted cobalt molybdate catalyst (Fe0 03Co0.9 7MoO4) was studied by Maksimov et al. [195,196] with respect to the role of iron in the transfer of charge. Iron strongly enhances the catalytic activity and at the same time increases the conductivity by a factor of 100. Mossbauer spectroscopy reveals that 4% of the iron ions are present as Fe2+ impurity . This fraction is doubled at steady state reaction conditions, and indicates participation of iron in the charge transfer process. 

We may conclude that the divalent cobalt ions move out into the large cavities upon adsorption of NH3 to form a hexacoordinate cobalt(II)-ammonia complex. Following adsorption of 02 in the ammoniated Co(II)Y zeolites, oxygen enters the coordination sphere of the Co2+ ions. This is accompanied by a charge-transfer process to form a [Co(III) (NH3)502 ]2+ complex. The general intermolecular redox process can be approximated by the reactions... 

Of the mononuclear complexes perhaps the most interesting are [IrCls]3 and the complex cobalt hydrides since in both cases cyclic reactions have been observed. For [IrCl6]3-, hydrogen and chlorine are formed on irradiation with 254 nm light, apparently by processes involving free radicals (equations 8-15).70 The photochemical excitation probably involves L-M charge transfer. 

Reaction of Cytochrome cimu with Tris(oxalato)cobalt(III) The cytochrome c protein was also used as reductant in a study of the redox reaction with tris (oxalato)cobalt(III).284 Selection of the anionic cobalt(III) species, [Conl(ox)3]3 was prompted, in part, because it was surmised that it would form a sufficiently stable precursor complex with the positively charged cyt c so that the equilibrium constant for precursor complex formation (K) would be of a magnitude that would permit it to be separated in the kinetic analysis of an intermolecular electron transfer process from the actual electron transfer kinetic step (kET).2S5 The reaction scheme for oxidation of cyt c11 may be outlined ... 

The cyclobutadiene derivatives [Co(Tj -C4Fc Ph4 )Cp] (n = 1-3) (Cp = 17 -cyclopentadienyl) undergo one-electron oxidation to stable cations (27) which show charge-transfer bands in the near infrared region. An analysis of the spectra led to the conclusion that the cations are Class II mixed-valence compounds and that the charge-transfer transition arises from a weak interaction between Co(I) and Fe(III) rather than between Fe(II) and Fe(III). Each compound showed further oxidations at more positive potentials, including an irreversible process ascribed to electron loss from the cobalt center. 

In [13a], a triplet-triplet exchange interaction requiring orbital overlap is the proposed quenching process. The very efficient quenching observed in [13c] occurs via formation of a charge transfer Intermediate, in which the zinc moiety is reduced by the cobalt system. The lifetime of this intermediate is estimated to... 

Similar studies using differently functionalized pyrene and iron or cobalt porphyrins were proposed to obtain integrated SWCNT nanohybrids [128] and, very interestingly, the use of multi-walled CNTs (MWCNTs) produced remarkable results as well [129, 130]. Complexes of MWCNTs and pyrene were obtained and combined with metallo-porphyrins, giving rise to charge separated species upon photoexcitation. MWCNTs are easier to process and their electrOTiic structure is more suitable to achieve charge transfer and transport due to the presence of concentric internal graphitic layers. 

Typically, those ferrocenyl-porphyrins have been explored in photoinduced electron transfer and charge separation processes mimicking the activity of the photosynthetic system, as well as in the development of catalysts for multielectron transfer reactions. Ferrocenyl substituents were shown to enhance the electrocat-alytic activity of cobalt [41, 42], iron [43], and copper [44—46] porphyrins for tetraelectronic reduction of dioxygen to water. 

Graphene adsorption on cobalt is a chemisorption process as evidenced by the partial DOS and Bader charge analysis meanwhile, the charge transfer and the shifts in the Fermi level and electronic levels were evidenced by the vibrational analysis. The vibrational analysis has revealed the vibrational modes within the sheets are weakened while the modes perpendicular to the surface are strengthened. 

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