Blue species oxidation

As mentioned above, the Pt(2.25+)4 species (B1 and B2) possesses one unpaired electron of Pt(III) (S = 1/2) and is the only species which exhibits paramagnetism among the four oxidation states. The ESR spectrum of the ce-pyridonate-blue species shown in Fig. 7 exhibits an axial signal characteristic of the platinum-blues (g = —2.4 and g = —2.0) (48, 49, 70, 96). Similar signal patterns are also observed for several other blue compounds (34, 47, 57, 86, 88, 89), and these common features show that the unpaired electron resides on the dz2 orbital located along the Pt chain. The g values observed for the para-... 

Imposition of a hexakis(thioether) environment results in surprising redox behavior. Electrochemical studies reveal a quasi-reversible one-electron oxidation at + 1.30 V vs SHE [114-116]. Electrochemical or chemical (Ce(IV)) oxidation of [Ag(9S3)2] affords an unstable paramagnetic blue species of unknown structure. Besides increasing the electron density at the metal ion (because of the high coordination number), coordination to 9S3 may promote this oxidation by binding tightly. Oxidation may decrement the stability of the complex, but not so much that the oxidized form cannot exist in solution. 

Treffry A, Zhao Z, Quail MA, Guest JR, Harrison PM. 1995. Iron(ll) oxidation by H-chain ferritin evidence from site-directed mutagenesis that a transient blue species is formed at the dinuclear iron center. Biochemistry 34 15204-15213. 

It is of interest to note that when solutions of ascorbic acid and the polymer which have been treated with a sequestering resin are allowed to react, the rate is much lower, indicating the importance of the role of the metal ions. A probable inference from this is that most if not all studies of oxidation effects of L-ascorbic acid have involved metal-ion catalysis (presumably by iron or copper ions). The function of the ascorbic acid in such systems would then be to regenerate the Fe or Cu ions which are the actual catalysts. In the reaction of iron(iii) with penicillamine, redox reactions involving molecular oxygen are observed in basic media with the formation of red complexes. In acid conditions, however, a less stable blue species is observed. 

The addition of excess (H30)C104 to 2 (at -35 C in MeCN) yields an intense blue species (5) that exhibits the electrochemistry (curve c, Figure 1) of oxidized iron (III)-porphyrin [Fe (CIbTPP ) ], The new redox couples of 2 are absent from the cyclic voltammogram for 5, which is equivalent to that for (Cl8TPP)Fe MCIO4) (curve a. Figure 1). 

A few substances indicate the presence of a specific oxidized or reduced species. Starch, for example, forms a dark blue complex with 13 and can be used to signal the presence of excess 13 (color change colorless to blue), or the completion of a reaction in which 13 is consumed (color change blue to colorless). Another example of a specific indicator is thiocyanate, which forms a soluble red-colored complex, Fe(SCN) +, with Fe +. 

The pale blue tris(2,2 -bipyridine)iron(3+) ion [18661-69-3] [Fe(bipy)2], can be obtained by oxidation of [Fe(bipy)2]. It cannot be prepared directiy from iron(III) salts. Addition of 2,2 -bipyridine to aqueous iron(III) chloride solutions precipitates the doubly hydroxy-bridged species [(bipy)2Fe(. t-OH)2Fe(bipy)2]Cl4 [74930-87-3]. [Fe(bipy)2] has an absorption maximum at 610 nm, an absorptivity of 330 (Mem), and a formation constant of 10. In mildly acidic to alkaline aqueous solutions the ion is reduced to the iron(II) complex. [Fe(bipy)2] is frequentiy used in studies of electron-transfer mechanisms. The triperchlorate salt [15388-50-8] is isolated most commonly. 

In analogy to the situation for bipyridine, the blue tris(l,10-phenanthroline)iron(3+) ion [1347949-7], [Fe(phen)2], must be obtained by oxidation of the corresponding iron(II) ion. [Fe(phen)2] has an absorption maximum at 590 nm, an absorptivity of 600 (Mem), and a formation constant of 10 . In solutions of pH > 4, this species is reduced to the iron(II) complex. The reduction is instantaneous in alkaline solution. At pH < 2, protons compete with iron(III) for the phenanthroline nitrogens and coordination is incomplete. [Fe(phen)2] is used most often in solution as an oxidant, but the trichloride [40273-22-1] and the triperchlorate monohydrate [20774-81-6] salts have been prepared. 

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