Oxidation state fractional

Where it is not feasible to define an oxidation state for each individual member of a group, the overall oxidation level of the group is defined by a formal ionic charge to avoid the use of fractional oxidation states for example, Oy. 

The only example of xenon in a fractional oxidation state, +, is the bright emerald green paramagnetic dixenon cation, Xe [12185-20-5]. Mixtures of xenon and fluorine gases react spontaneously with tiquid antimony pentafluoride in the dark to form solutions of XeF+ Sb2 F, in which Xe is formed as an iatermediate product that is subsequently oxidized by fluorine to the XeF+ cation (83). Spectroscopic studies have shown that xenon is oxidized at room temperature by solutions of XeF+ ia SbF solvent to give the XE cation (84). 

PALLADIUM IN NEGATIVE AND FRACTIONAL OXIDATION STATES 6.4.8.1 Phosphorus... 

Unfortunately, whatever the metallocenium and the metal bis-dithiolene moiety, no fractional oxidation state compound with formula (Cp 2M ) [M(M02] (with x < 1) has been reported in the literature. Concerning (Cp 2M )[Ni(dmit)2] (M = Fe, Cr, Mn), all our attempts to obtain chemically or electrochemically (Cp 2M )x[Ni(dmit)2] (with x < 1) have resulted in the synthesis of noncrystalline samples as sticky powders or mixture of fibers and grains, whose characterization was not possible. Therefore the combination between M(dmit)2 and metallocenium has been unsuccessful to obtain magnetic molecular conductors. 

To our knowledge, there are less than 30 compounds based on radical-cations and M(dmit)2 systems (Table 2). Most of them contain divalent or monovalent M(dmit)2 units, and only a few of them have been structurally and magnetically characterized. Since they are not in a fractional oxidation state, they behave as insulators with low room-temperature conductivity. 

Evidently, the most interesting materials are those in a fractional oxidation state, with general formula (cation)[M(dmit)2] (n > 1), since they can exhibit both electrical and magnetic properties. Only eight such complexes have been reported so far. All of them but (BDTA)[Ni(dmit)2]2 [89] have been obtained as powders. They have in general been poorly characterized, and their stoichiometries have been determined from elemental analysis. Among these powdered compounds, the... 

Although combined with [Ni(dmit)2], none of the above-mentioned compounds exhibit electrical properties, since they are 1 1 materials without any charge transfer. One of the first attempts to obtain fractional oxidation state compound was performed by us in 2006 [101]. [Fe(sal2-trien)][Ni(dmit)2]3 has been obtained by electrocrystallization from an acetonitrile solution of [Fe(sal2-trien)][Ni(dmit)2], This compound behaves like an SC (ctrt = 0.1 S cm ) but does not exhibit any spin transition. This seems to be due to the statistical disorder of the whole Fem complexes, which prevents the occurrence of short contacts between cations. 

Chronologically, Sato and coworkers have been the first to obtain and to characterized unambiguously a fractional oxidation state compound containing the Ni (dmit)2 unit and an SCO cation, namely [Fe(qsal)2][Ni(dmit)2]3.CH3CN.H20 [106]. This complex has been obtained after electrocrystallization from an acetonitrile solution of [Fe(qsal)2][Ni(dmit)2].2CH3CN. 

The use of another SCO Fera complex [Fe(salEen)2]+ has afforded the fractional oxidation state compound [Fe(salEen)2]2[Ni(dmit)2]5.6CH3CN [104]. The latter is... 

The oxidation number of S in S4Og (tetrathionate) is +2.5. The fractional oxidation state comes about because six O atoms contribute —12. Because the charge is —2, the four S atoms must contribute +10. The average oxidation number of S must be +x = 2.5. 

It will be clear from Table 11 that mixed oxidation state complexes need not contain equal numbers of Au1 and Au111 centres, and fractional oxidation states between I and III may be observed.163,165,300,425 The mixed oxidation state complexes can, in many cases, be distinguished from true Aun complexes by 197Au Mossbauer spectroscopy or by ESCA.4,23,428-429... 

It has long been known that sulfur, selenium, and tellurium will dissolve in oleums to give blue, green, and red solutions, respectively, which are unstable and change in color when kept or warmed. The colored species are cyclic polycations in which the element is formally in a fractional oxidation state. It is difficult to isolate solids from oleum solutions, and crystalline salts can be much more easily obtained by selective oxidations of the elements with SbF5 or AsF5 in liquid HF or S02,7 or with 82( 2 in HSO3F. 

The three fluoro-acids HF, HS03F and CF3S03H have proved to be fruitful and essential media for preparation of many compounds of ionic species of transition metals in unusually high or low oxidation states and of cations of non-metallic elements in fractional oxidation states. 

In the sections above there has been frequent reference to base-induced disproportionation of transition metal cations in low oxidation states (Sec. 11.3.4.2), of carbonyl cations of transition metals (Sec. 11.3.4.3) and of polyatomic cations of non-metals in fractional oxidation states (Sec. 11.3.4.4). In the last-named section, disproportionation of polyiodine cations was presented and discussed in considerable detail but a similar rationale can be applied to stability of all cations — metallic or non-metallic — in unusually low or fractional oxidation states, whether produced in non-aqueous ionising media or as naked cations. 

Thus, disproportionation occurs when a highly electrophilic polyatomic non-metal cation interacts with a nucleophilic base to form, in the first instance, a polyatomic cation of lower charge per non-metal atom (lower fractional oxidation state) and a compound, essentially covalent, formed between the base and the non-metal of the cation, with that non-metal now in a higher oxidation state than in the parent cation. For example It disproportionates to IJ and IF5. With greater availability of base, the polyatomic cation first formed will disproportionate to a lower-charge polyatomic cation and ultimately to the free element from which the parent cation was formed. Similar patterns differing in detail, are observed for metallic polyatomic cations, monatomic transition metal cations in low oxidation states and for all naked electrophilic cations. 

The usual reversibility of disproportionation reactions with increase in acidity provides an effective general route to synthesis of cations in low or fractional oxidation states, as was shown for preparation of Au"+ in Sec. 11.3.4,3 and for iodine cations in Sec. 11.3.4.4. 

III. Compounds of Gold in Fractional Oxidation States Gold Clusters. 243... 

In the case of DA compounds, both donor and acceptor molecules may undergo oxidation towards fractional oxidation states. In general, their half wave potentials are similar and formation of the DA compound may compete with crystal growth of FOSC phases. This feature was illustrated in the case of TTF[Ni(dmit)2]2. Single crystals of this phase were electrocrystallized using TTF and TBA[Ni(dmit)2]. The cyclic voltammogram of each compound shows that [Ni(dmit)2] is oxidized at a potential 120 mV lower than that of TTF. However, addition of TTF to a solution of (Bun)4[Ni(dmit)2] inhibits the formation of the (Bun)4 o.29[Nl(dmit)2] FOSC phase in favor of the TTF[Ni(dmit)2]2 one.76... 

Figure 4.18 Synthesis of the [dmit] ligand, its storable derivatives and [M(dmit)2] compounds. (FOSC = fractional oxidation state compound DA = donor-acceptor compound)...

A large number of C [M(dmit)2] complexes (n = 2, 1, 0) have been prepared. " The dianion salts [R4N]2[M(dmit)2] can be obtained by treating a solution of Na2dmit in methanol with the appropriate M metal salt and the appropriate tetraalkylammonium bromide (Figure 4.18). The corresponding monoanionic salt [R4N][M(dmit)2] is obtained from the dianionic salt by iodine oxidation. Further oxidation may lead to the neutral complex or to fractional oxidation state compounds (FOSCs) or donor-acceptor (DA) compounds. These oxidation steps are described in Section 4.3.2. 

Metal bis-dithiolene complexes exhibiting conducting or superconducting properties can be neutral or in a fractional oxidation state. In FOSCs, the associated cation is of the closed-shell type, while in DA compounds, the metal bis-dithiolene is an acceptor and the donor is an open-shell cation. As already mentioned in Section 4.2.2.3, the most encountered... 

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