Polyanions organic

The coefficients Co, nnd C2 (denoted as mq, ai, and aj in Ref. 33) are influenced by various molecular properties of the solvent and an ion, including their electron-donating or accepting abilities. Hence, these coefficients are specific to the ion. Nevertheless, they may be considered as common to a family of ions such as the polyanions whose surface atoms, directly interacting with solvents, are oxygens. This is the case for hydrated cations or anions whose surfaces are composed of some water molecules that interact with outer water molecules in the W phase or with organic solvents in the O phase. 

Links between atoms serve to compensate for the lack of the electrons which are necessary to attain the electron configuration of the next noble gas in the periodic table. With a common electron pair between two atoms each of them gains one electron in its valence shell. As the two electrons link two centers , this is called a two-center two-electron bond or, for short, 2c2e bond. If, for an element, the number of available partner atoms of a different element is not sufficient to fill the valence shell, atoms of the same element combine with each other, as is the case for polyanionic compounds and for the numerous organic compounds. For the majority of polyanionic compounds a sufficient number of electrons is available to satisfy the demand for electrons with the aid of 2c2e bonds. Therefore, the generalized 8 —N rule is usually fulfilled for polyanionic compounds. 

Molecules such as P4 and the polyanionic clusters such as Si4- or As2- that are discussed in Section 13.2 are representatives of electron precise closo clusters. Organic cage molecules like tetrahedrane (C4R4), prismane (C6H6), cubane (C8H8), and dodecahedrane (C20H20) also belong to this kind of cluster. 

Electro-organic chemistry at the cathode is essentially that of radicals, radical-anions, carbanions, and polyanions (which range from dianions to hexa-anions (Scheme 1). The anions may behave as nucleophiles, bases, and as single electron reductants the factors governing the competition between these roles are not yet fully understood. 

The number of complexes of this type is legion. The general formula is [XMhZ(L)039]" (or [X2Mi7Z(L)06i]"-) where Z is a secondary heteroatom and L is a terminal ligand on Z. In some cases L is another lacunary polyanion, an organic or organometallic moiety, or is absent. Scheme 5 illustrates some of the possibilities. 

Within the last few years there has been considerable activity directed towards the synthesis of organic and organometallic derivatives of heteropolyanions. Reactions of lacunary polyanions with RMC13, where R is an organic or organometallic radical, provide a simple route to such derivatives.97 Some examples of these reactions are presented in Scheme 5. For the most part the reactions proceed smoothly and the products are remarkably stable towards hydrolysis. Apart from their structural characterization via crystallography and NMR spectroscopy the chemistry of these complexes has not been completely described. 

The introduction of organic and organometallic moieties into lacunary polyanion structures has been described in Sections 38.4.2.1 and 38.4.2.2. Other organic derivatives of polyanions are discussed in the following sections. 

Because the surfaces of polyanions have some similarities to those of metal oxides, it is thought they may have some relevance in the area of heterogeneous catalysis. As a result a whole new area concerned with the synthesis and study of organic and organometallic derivatives of polyanions is being investigated.173... 

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