Dianions compounds, properties

Two classes of charged radicals derived from ketones have been well studied. Ketyls are radical anions formed by one-electron reduction of carbonyl compounds. The formation of the benzophenone radical anion by reduction with sodium metal is an example. This radical anion is deep blue in color and is veiy reactive toward both oxygen and protons. Many detailed studies on the structure and spectral properties of this and related radical anions have been carried out. A common chemical reaction of the ketyl radicals is coupling to form a diamagnetic dianion. This occurs reversibly for simple aromatic ketyls. The dimerization is promoted by protonation of one or both of the ketyls because the electrostatic repulsion is then removed. The coupling process leads to reductive dimerization of carbonyl compounds, a reaction that will be discussed in detail in Section 5.5.3 of Part B. 

More recently, Stepanov et al. (1989) investigated the acid-base properties of the zwitterion 3.22 which is obtained in the diazotization of 5-amino-3-nitro-l,2,4-triazole. Under alkaline conditions the (Z)-diazoate dianion 3.23 is formed. It can be isomerized thermally to give the (E)-diazoate dianion 3.24. If the solution of this compound is acidified, the primary addition of a proton takes place at the anionic ring nitrogen yielding 3.25, and subsequently the hydrogen-bond-stabilized (Z)-iso-mer (3.26). Further acidification gives the nitrosoamine (3.27). 

One of the most important properties of quinoid compounds is the two step redox reaction. Quinoid compounds undergo one electron reduction to so-called semiquinone anion radicals, and further one electron reduction of semiquinone anion radicals gives dianions (Scheme 14). 

The calculations also bring to light a significant U ( = ) interaction between the metal center and the C=C bond of the endo dithiolene ligand in the U(V) anionic complex, which does not exist in the dianionic species. Again, magnetic properties of these air-sensitive compounds were not investigated. 

The Fe(III) complexes of the dianion of pyruvic acid thiosemicarbazone (thpu2- Fig. 7), (cation+)[Fe(thpu)2]-nH20, are very similar to those of the salicylaldehyde derivatives (Fig. 6) discussed above. The spin state properties are quite sensitive to changes in the counter-cation (typically an alkali-metal cation or a protonated nitrogenous base) and the lattice water content of the material. The parent compound, NH4[Fe(thpu)2], is low spin at room temperature [113]. Li[Fe(thpu)2]-3H20 is also low spin but K[Fe(thpu)2] 2-H20 shows almost complete spin crossover between 80 and 300 K [108]. 

In recent years, the first distannynes have been obtained. Reduction of 2,6-di(2,6-diisopropylphenyl)phenyltin(ll) chloride (Ar SnCl) or 2,6-di(2,4,6-triisopropylphenyl)phenyltin(n) chloride (ArSnCl) with sodium or potassium has given not only the stannynes Ar Sn=SnAr and ArSn=SnAr, but also the radical anion [ArSn=SnAr, and the dianions [ ArSn=SnAr] and [Ar Sn=SnAr ]=.534 The properties of the Ar compounds are as shown in Table 11. 

X -phosphorins have physical properties which are rather similar to those of pyridines. But the chemistry of X -phosphorins is very different, due mainly to the phosphorus atom which can easily lose one electron to produce a stable radical cation, or accept one or more electrons to yield a radical anion, dianion or radical trianion. Nucleophiles add to stable X -phosphorin anions. In contrast to pyridine chemistry, no stable X -phosphorinium compound (corresponding to a N-alkyl-pyridinium salt) could be isolated. Instead the electron shell of phosphorus is enlarged by addition of an electrophile yielding a X -phosphorine derivative. 

The compound Os3(CO)j j(C5H5N) is very soluble in acetonitrile, dichl-oromethane, acetone, and methanol, and its solutions are stable to air. It is sparingly soluble in hydrocarbons. Its purity can be checked by IR spectroscopy (dichloromethane solution) v(CO)cm 1 2106(w), 2052(s), 2035(vs), 2008 (s), 1976 (m). Other physical properties have been reported.2 The vacuum pyrolysis of this compound provides a high-yield route to the carbido-dianion [Os10C(CO)24]2-.5... 

The 46-kDa monomeric tyrosinase of Neurospom contains a pair of spin-coupled Cu(II) ions.568 569 The structure of this copper pair (type 3 copper) has many properties in common with the copper pair in hemo-cyanin.569a For example, in the absence of other substrates, tyrosinase binds 02 to form "oxytyrosinase," a compound with properties resembling those of oxyhemocyanin and containing a bound peroxide dianion.569... 

Neutral square coplanar complexes of divalent transition metal ions and monoanionic chelate or dianionic tetrachelate ligands have been widely studied. Columnar stack structures are common but electrical conductivities in the metal atom chain direction are very low and the temperature dependence is that of a semiconductor or insulator. However, many of these compounds have been shown to undergo partial oxidation when heated with iodine or sometimes bromine. The resulting crystals exhibit high conductivities occasionally with a metallic-type temperature dependence. The electron transport mechanism may be located either on predominantly metal orbitals, predominantly ligand re-orbitals and occasionally on both metal and ligand orbitals. Recent review articles deal with the structures and properties of this class of compound in detail.89 90 12... 

A wide range of metal dithiolene complexes have been prepared and their electrical conduction properties reported.111-114 They include neutral, monoanion and dianion complexes with a variety of substituents on the ligand (R = Ph, Me, CN, H, CF3) and a variety of cations. The choice of cation has often been determined by the desire to obtain easily crystallized products and has resulted in the use of rather bulky substituted ammonium salts. The compounds behave as semiconductors with relatively low conductivities at room temperature. It has been shown that the monoanion complexes are considerably more conducting than either the corresponding neutral complex or the dianion, and Rosseinsky and Malpas have proposed that this is related to the ease of disproportionation.113... 

Ionic compounds can also gelate solvents, perhaps one of the nicest examples being that of dicationic gemini surfactants in which tartrate is used as the counterion and source of chirality [158], because it shows the very important role of chirality on the property of the salt. When either d- or L-tartrate dianions and dimers of cetyltrimethylammonium cations are combined, stable gels are formed in chlorinated solvents, but neither the mixture of enantiomers nor the meso tartrate form a gel. The structure of the gelator... 

The electronic structure of dithiolene complexes is of crucial importance in determining the electron transfer in the derived compounds exhibiting interesting physical properties. Bis(l,2-dithiolene) metal(II) complexes, for example, may be isolated as dianions, monoanions, and neutral species... 

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