Homoatomic anions

An elegant access to larger cluster units is to make use of preformed smaller clusters as they occur, e.g., in Zintl phases [8, 9]. The phase KSi (or K4Si4) contains homoatomic Si4 tetrahedra, and thus a salt-like formulation (Na )4[Si4]" with a formal electron transfer is appropriate (Fig. 1) [10]. Such homoatomic anionic building blocks occur in binary or ternary intermetallic phases A E and A Pn j with A being an alkali and alkaline-earth metal, and E = Si-Pb and Pn = P-Bi. These phases are generally available in good quantities, and - since a few members... 

Kraus has shown that many of these compounds of the alkali metals with the less electropositive metals (some of which are soluble in liquid ammonia) possess many of the properties of typical salts. He calls these salts of homoatomic anions. It should be noted that in handbooks or indexes, these compounds are to be found... 

The increasing complexity of these homoatomic anions is well reflected by the following systematic names ... 

Both of these are examples of heteroatomic anionic rearrangements, that is, ones where X and Y are different. Homoatomic anionic rearrangements, where X = Y, are also possible. The one example known before the discovery of organometallic migrating groups was the C—C anionic rearrangement (//, S6), reviewed by Grovenstein elsewhere in this volume ... 

The occurrence of homoatomic anions [En] of the elements of groups IV (C, Si, Ge, Sn, Pb) and V (P, As, Sb, Bi) as constituents of Zintl phases is well knownJ Despite numerous attempts, just a few of the En clusters have been isolated as uncharged molecules E Rx from the Zintl phases by reaction with suitable agents such as alkyl chlorides. 

Fig. 3.1 The plot of parameter D vs. parameter N. The plot contains elements (x), cations without homoatomic bonding ( ), anions without homoatomic bonding (O), cations with homoatomic bonding ), anions with homoatomic bonding (O), and ideal structures +). The definitions of some of the ideal structures are as follows, ideal rutile the oxygen positions of the ideal...

Fig. 3.7 Plot of the D parameter of cations (DJ against the D parameter of anions (Da) for selected binary structures. Compounds with homoatomic bonds are excluded.

There are three kinds of rings of different nuclearity known for homoatomic group 15 anions (Fig. 7). For arsenic, three-, five-, and six-atom rings are described in solid state compounds, and for phosphorus only the six-atom ring is reported, whereas for antimony and bismuth no homoatomic rings are known in neat solid state materials of alkali and alkaline earth metals. 

In the past decades, homoatomic polyanions in solid state compounds of group 14 elements have been a powerful starting material toward different kinds of chemical transformations. Recent developments, especially for nine-atom clusters, have been discussed elsewhere [5,125,126] and are not within the scope of this review. Here, we concentrate on neat solvates , which means that in addition to cation and anion... 

If one compares the N-e values of solvate compounds that contain homoatomic poly anions, it becomes evident that there seems to be a border that has not been... 

Structures of Soluble Homoatomic Zintl Anions of Group 14 and 15 Elements.95... 

Table 2 Structurally characterized homoatomic tetrel and pentel element cluster anions obtained from solutions...

All other homoatomic Pn cluster anions are cage molecules with localized two-center-two-electron bonds. The cyclic [PnJ anion has been characterized by NMR spectroscopy for Pn = P [210], and structures are known for Pn = P, As, Sb, Bi (Table 2). A planar [Ps] anion has only been detected in solution by P NMR spectroscopy [210]. Envelop-shaped five- and six-membered rings are found for [Pns] and [Pe]", whereas [Asg]" deviates only slightly from planarity and has a chair conformation. The aromaticity of the planar anions [P4] and [Pe]" is distinct from that of regular 671-aromatic hydrocarbons and has been described... 

Soluble heptapnicanortricyclane anions [Pny] (Fig. 3a) and trishomocubane-shaped (ufosane-like) anions [Pnn] (Fig. 3d) are very common and known as in the binary solids for Pn = P, As, Sb (Table 2). Oxidative coupling of these monomers leads to the dimers [Pny-Pny]" and [Pnn-Pnn]" for Pn = P and As (Fig. 3b, e), which - as observed for the tetrel element clusters - have an external homoatomic bond, but in this case the structures of the monomeric units are fully retained upon dimerization. A trimeric oxidative coupling product of [Py] is the... 

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