Polytellurides

In contrast to the polysulfides and almost all the polyselenides (exception Cs4Sei6 ), a number of polytelluride anions are also known with total negative charges greater than 2, as, for instance, in NaTe with discrete [Tcs] ions and in 83X022 with polymeric sheet-Uke [Tcg ] ions. These are examples for the striking variety of structural motifs and formula types (x/y = 5/3, 1/1, 2/3, 2/5, 1/3, 1/4, 1/6, 2/13, 1/7 and 3/22) that are known for the alkali metal polytellurides A TCj, and which reflect the propensity of tellurium both to catenate and to participate in hypervalent coordination polyhedra. Whereas discrete anions are observed for xjy 2/3, polymeric chain and lamellar anionic networks are present in such tellurides when xfy 2/5.  

The pronounced bond length alternation within the anion sheets of RbTee is in stark contrast to the modest difference between the Te Te distances (di = 300.3(1), d2=307.7(l) pm) belonging to the planar thinned nets 

The resulting count of 40 electrons per Teg units (i.e., 4x6 electrons for the Te° squares and 2x8 electrons for the two terminal Te atoms of the Teg chains) corresponds to the observed [Te ] formulation for the component polytelluride sheets of Cs4Te2g. An alternative way of deriving the preferred electron count for networks of heavy main group elements consisting of finite-length linear chains is to employ an electron-rich multicentre bonding 

Metal sulfides and polysulfides have been extensively studied because of their key role in important catalytic processes such as the hydrodesulfurization of crude oil or the biosynthesis of metalloproteins. The coordination chemistry of polysulfides has been comprehensively reviewed similar to that of the heavier polychalcogenides. Polysulfido complexes are themselves reactive and their exothermic desulfurization can be exploited as a means of 

Alternatively, the polychalcogenide may be generated in situ and then allowed to react immediately with the appropriate metal compound.  

The unit cell of Cs3Te22 is depicted by the grey lines 

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The synthesis, structural characterization and coordination chemistry of polyselenides, Se, and polytellurides, Te t , is a burgeoning field which has sprung into prominence during the past decade. The seminal studies by E. Zintl and his... 

There is also a bewildering variety of structural motifs in polytelluride-ligand complexes as the brief selection in Fig. 16.10 indicates the original papers should be consulted for preparative routes and other details. Thus, dissolution of the alloy K2Hg2Te3 in ethylenedi-amine, followed by treatment with a methano-lic solution of [NBu JBr, yields the dark brown... 

Figure 16.10 Structures of some metal-polytelluride complexes.

Polychalcogenides are less stable than polysulfides (p. 681). Reaction of alkali metals with Se in liquid ammonia affords M2Se2, M2Se3 and M2Se4, and analogous polytellurides have also been reported (see preceding section). However many of these compounds are rather unstable thermally and tend to be oxidized in air. 

Complex equilibria among multiple species are typical also of polyselenide and polytelluride solutions. Aqueous polyselenide solutions have been employed as electrolytes in high-elRciency PEC with photoanodes made of gallium arsenide and cadmium chalcogenides (Chap. 5). Unlike polysulfides, the fundamental equilibria constraining the distribution of polyselenide species have not been meticulously characterized [19]. 

All the dialkali monosulfides are soluble in water and give alkaline solutions. The tellurides are instantly decomposed by air. They are soluble in water, but the solutions are easily oxidized to red polytellurides. The alkali metal tellurides are strong reducing agents which reduce tellurites to metallic tellurium. 

Smith DM, Ibers JA (2000) Syntheses and solid-state structural chemistry of polytelluride anions. Coord Chem Rev 200-202 187-205... 

The Gillespie-Nyholm rules usually can also be applied to other polyanionic compounds with hypervalent atoms. As an example, some polytellurides are depicted in Fig. 13.6. The Te

[Pg.136]

Structures of some polytellurides. Lone electron pairs are marked by double dots. Te2 also forms simple chain structures like Sj... 

M. G. Kanatzidis, From cyclo-Te8 to Te" sheets are nonclassical polytellurides more classiscal than we thought Angew. Chem. Int. Ed. 34 (1995) 2109. 

The method (i) can be applied to the synthesis of almost all heavy ketones (Tables 3-5). Silanethiones and a silaneselone stabilized by the coordination of a nitrogen group have been synthesized by the method (ii) (Table 4). The method (iii) is effective to the synthesis of kinetically stabilized tricoordinate heavy ketones, although it cannot be applied to the synthesis of double-bond compounds between heavier group 14 elements and tellurium due to the instability of polytellurides (Table 3). The method (iv) can be used only when the unique dilithiometallanes can be generated (Table 3). The synthesis of heavy ketones by the method (v) demands the isolation of the corresponding heavy acyl chlorides as stable compounds (Table 5). 

Cs3Se22 has recently been prepared under methanolothermal conditions138 and is isostructural to Cs3Te2219. In contrast to the [Te ] sheets (Figure 10b) of the polytelluride, the anionic sheets in Cs3Se22 are best described as [(Se3-)(Se3-)], in which disordered pairs of bent Se3 radical anions and Sef anions are linked through secondary interactions. 

Polysulfoxides, 23 733-735 optically active, 23 735 Polysulfoximines, 23 745-746 Poly(sulfur nitride), as organic semiconductor, 22 212 Polytellurides, 24 408 Poly-Tergent, commercial defoamer,... 

Only species Te 2- with short chains (n = 2-4) are present in polytelluride solutions [57]. Despite this fact many Zintl-type valence precise tellurium dianions of higher nuclearity have been isolated in the solid state in the presence of suitable counter cations. The three general synthetic routes to such polytelluride anions can be summarized with representative examples as follows ... 

Polytelluride Anions With Cluster-like Building Units... 

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