Tetrel elements

Scharfe S, Eassler TP (2010) Polyhedral nine-atom clusters of tetrel elements and intermetalloid derivatives. Phil Trans Royal Soc A Math Phys Eng Sci 368 1265-1284... 

Smaller tetrel element clusters like the tetrahedral [E4] ions were observed for the first time in the alloy NaPb [38] and are present in AE phases for E = Si to Pb and A = Na-Cs. Although these phases are not soluble, ammoniates of [Pb4]" have been obtained from liquid ammonia solutions of the binary phase RbPb [39]. The Zintl phases Ai2Sii7 (A = K, Rb, Cs) and KgRb6Sii7, which in the solid state contain [Si4]" and [Sig]" anions in the ratio 2 1, readily dissolve in liquid ammonia, and recently it has been shown that both cluster anions [Si4]" [37] and [Sig]" [40] are retained in solution. Corresponding pentel element clusters in bulk solids are [Pn7] and [Pnn] (Table 1). 

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... 

Zintl Anions, Ligand-Stabilized Cage Compounds, and Intermetalloid Clusters of the Tetrel Elements... 

This chapter reviews the synthesis, structures and physical properties of homoatomic Zintl ions and recent developments in the formation of mixed clusters consisting of the tetrel elements Ge, Sn, and Pb and various d-block elements. A brief summary is provided of the chemistry of homoatomic clusters (this has been reviewed earlier [1,2]), with the main focus being oriented towards the latest results in the field of intermetalloid clusters [3, 4]... 

In a salt-like description of these compounds, AE, the alkali metal A transfers its valence electron to the tetrel , and - in agreement with the Zintl-Klemm-Busmann concept [9] - the tetrel elements form P4-analogous tetrahedral clusters [ 4] . These highly charged clusters [ 4] are retained in a liquid ammonia solution of RbPb, as shown by Korber et al. via the crystallization of the ammoniate Rb4Pb4(NH3)2 [10]. The isotypic compounds A4Sii4(N 143)2 were obtained for A = Rb and Cs from reactions of the element Sn, as well as from Cs with Sn(C6Hs)4 in liquid ammonia [10]. 

Soluble Zintl ions can also be obtained by electrochemical methods using the respective element as cathode material [34, 60, 61], or through the reaction of the various modifications of the tetrel (Sn and Pb) and pentel (P, As, Sb) elements with dissolved or finely dispersed alkali or alkaline-eatth metals in solution [62] as well as in molten crown-ethers [63]. 

Beside the most frequent soluble tetrel and pentel element clusters listed in Table 1, other homoatomic polyanions have been isolated from solution. An overview is given in Figs. 2 and 3 for group 14 and 15 elements, respectively, and in Table 2. The smaller tetrel clusters [Es] and [Eio] have been isolated as A-crypt salts (Fig. 2b, e, respectively), and most probably they are formed upon... 

Table 1 Polyanions of tetrel and pentel elements of soluble Zintl phases ...

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

Some of the novel systems are known only with silyl, germyl or other inorganometallic substituents, but not with simple organyl substituents. Since no principal differences from the related organyl derivatives are expected, these compounds are also included in the present discussions. Excluded are compounds in which the tetrel exclusively bears halido, amido and alkoxo substituents or other hetero-element atoms with lone-pairs. 

In the meantime, homoatomic ligand-free Zintl clusters of tetrel atoms are known for compositions [ 4 , [ 5] , and [ g] with = Si, Ge, Sn, Pb and n = 2-4. A unique example of a cluster with ten vertices is [Pbio] with a bicapped quadratic anti-prismatic structure (Figure 3.1). The smallest clusters [ 4]" were first prepared in solid-state reactions of alkali metals (A = Na, K, Rb, Cs) with elemental tetrels ( = Si, Ge, Sn, Pb) in a 1 1 ratio [8]. 

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