Charge disproportionation

The chemistry of iron(IV) in solid-state materials and minerals is restricted to that of oxides, since other systems such as iron(IV)-halides are not stable [186]. Iron(lV) oxides are easy to handle because they are usually stable in air, but they often have a substoichiometric composition, with oxygen vacancies contributing to varying degrees. Moreover, the samples may contain different amounts of iron(lll) in addition to the intended iron(IV) oxide, a complication which may obscure the Mossbauer data [185]. Even iron(V) was found in iron(IV) oxides due to temperature-dependent charge disproportionation [188, 189]. 

Fig. 11 Schematic crystal packing of [CuII(hfac)2(TTF-CH=CH-py)2r for (a) homogeneous charge distribution and (b) charge disproportionated state...

Finally, some organocopper compounds undergo charge disproportionation under the influence of ligands that bind strongly to copper. Treatment of mesityl-copper with l,2-bis-(diphenylphosphino)ethane (DPPE), for example, results in the formation of bis(mesityl)copper anions and a copper cation to which four phosphorus atoms of two DPPE molecules are coordinated [75]. 

The spin integration results of Figure 5 indicate that when forming a tetrahedral Mn (Co) defect at Xu = 1/2, the migrating Mn (Co) approaches a +2 valence state while a neighboring octahedral Mn (Co) is oxidized toward +4. This constitutes a charge-disproportionation reaction which can be approxi-... 

A similar charge disproportionation reaction is reported to occur during the degradation of 5-LLMn204 with electrochemical cycling whereby the Mn + dissolves into the electrolyte. ... 

Using LFT, the change in the ligand-field stabilization energy (LFSE) for the charge disproportionation reaction (eq I) can be estimated for Mn and Co as shown in Figure 7. 

In sections 4, 5, and 7 it was shown how low-energy occupation and passage through tetrahedral sites by Mn is associated with the +2 oxidation state. It was also shown that Mnoct + can readily produce Mutet through charge disproportionation (eq 1). On the other hand, tetrahedral Mn with a +3 or +4 oxidation state was found to be less favorable. 

At Xu = 0.5. three of the eight TM ions (Mn. Co. and Ni) were found to undergo a major charge disproportionation reaction (eq 1) when moved from octahedral to tetrahedral coordination. In contrast, at Xu = 0 none were found to undergo charge disproportionation. 

Takano Y, Hiraki K, Yamamoto HM, Nakamura T, Takahashi T (2001) Charge disproportionation in the organic conductor, a-(BEDT-TTE)2l3. J Phys Chem Solids 62 393-395... 

Figure 2 The crystal structure of BaBiOs. The ordered charge-disproportionated larger and smaller BiOe octahedra are illustrated, as are the tilts of the octahedra about their shared comers.

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