Ferricenium cation

In most cases oxidation of uncharged borabenzene complexes produces cations which can only be observed electrochemically. The iron compounds 62 and 63 may serve as an example. Oxidation is fully reversible in rigorously dried CH2C12 but irreversible in more basic solvents such as THF and acetonitrile (62). Preparative oxidation with Ce(IV) salts cleanly produces monosubstituted ferricenium cations 64 (Scheme 10) (66). In contrast to the above mentioned boranediyl extrusions, the substituent at boron is retained here in the newly formed cyclopentadienyl ring. 

In principle it should be possible to determine the anisotropy of the paramagnetic susceptibility for some systems of pseudo-axial symmetry, but apart from the citation (74) of a private communication regarding the ferricenium cation, no experimental data are available for metal sandwich complexes. Such measurements should however be possible for at least some metallocenes and mixed sandwich complexes since these are found to crystallise in either a monoclinic (Fe(Cp)2 (6)) or orthorhombic (Ru(Cp)2, (Cp)V(Ch),... 

As before the data may be interpreted using the theory outlined above, but again understanding the listed k values as 11 23 and the results for the ferricenium cation and a number of substituted species are given in Table 19. 

Removal of an electron from neutral ferrocene can yield a large number of different ferricenium salts. This is a dramatic visual transformation, due to the vivid blue color of the ferricenium cation in contrast to the pale orange of ferrocene solutions. The cation displays two maxima 250 mp (<= = 12,000) and 617 mp (e = 340).18... 

Since the spectrum of the ferricenium cation is so distinctively different from that of ferrocene in halogenated solvents, no ion must be formed as yet and the 307 mu band must be due to a predissociative species probably close to that depicted as 3. 

The mechanism of reoxidation of reduced GO by ferricenium cations suggested by Bourdillon and co-workers 74) involves intermediate complex-formation between GO(red) (designated as FADH2 in Scheme 5) and ferricenium cation (designated as Q which transforms into ferrocene designated as P). Although no evidence for this has been obtained from the electrochemical data, the formation of the GO ferricenium intermediate has been kinetically proven in later... 

Horseradish peroxidase catalyzes the oxidation of ferrocenes into ferricenium cations by hydrogen peroxide according the stoichiometric Eq. (37) (113). 

A rather similar situation regarding the breakdown of Koopmans theorem exists for the metallocenes. The electronic structures of these interesting compounds have attracted the attention of both theoreticians and experimentalists for several years. Ferrocene is the metallocene that has been studied the most extensively. From the UPS standpoint this stems from the diamagnetism of the neutral molecule and the stability of the ferricenium cation. 

Reversible one-electron oxidation of ferrocene and its derivatives to cation radicals (so-called ferricenium cations) is a well-known reaction. The cation radical center is localized at the iron atom. In contrast to this statement, the hole transfers though conjugated systems were proven for the bis(ferrocenyl) ethylene cation radical (Delgado-Pena et al. 1983) and the cation radical of bis(fulvaleneiron) (LeVanda et al. 1976). Scheme 1-53 depicts these structures. 

Of particular interest is the effect that air exposure has on the Cp2Fe/NaY sample, as illustrated in Figures 14C, D the ferrocene is slowly oxidized (whether it is oxygen or water or both is still under investigation) to the ferricenium cation as reflected by the drop in intensity of the 440 nm ferrocene band and the concomitant growth of the characteristic 617 nm charge transfer absorption of Cp2 Fe+. 

Additional d electrons on the metals increase the number to be counted in the aromaticity formalism. As this can be applied by two metals (d6 - d8), the family of triple-decker sandwich complexes should consist of members having 30, 31, 32, 33, and 34 valence electrons. Analogous to the 17-valence-electron ferricenium cation, obtained by oxidation of ferrocene, 29-valence-electron species ( n,8/d5/7r8/d8/7r6) would be expected to be stable, and this has been confirmed by chemical and electrochemical studies (see Section III). 

Tamura H, Miwa M (1997) DNA cleaving activity and cytotoxic activity of ferricenium cations. Chem Lett 26(11) 1177-1178... 

In the 3 d sandwiches each of the three possible ground states, Ajg and Ajg, has been shown to exist in one or other of the complexes. The ferricenium cation exhibits a "2 (62 jg) ground state, and our own ) and other ) (ab initio) calculations satisfactorily reproduce this situation theoretically, although our results suggest that the mainly metal 3 d orbitals still follow the sequence... 

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