Tellurium polytellurides

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. 

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). 

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 ... 

Dilution with water reverses the reaction, and heating the solution liberates sulfur dioxide. Upon being added to a solution of tellurides, tellurium forms colored polytellurides. Unlike selenium, tellurium is not soluble in aqueous sodium sulfite. This difference offers a method of separating the two elements. Like selenium, tellurium is soluble in hot alkaline solutions except for ammonium hydroxide solutions. Cooling reverses the reaction. Because tellurium forms solutions of anions, Te2-, and cations, Te4+, tellurium films can be deposited on inert electrodes of either sign. 

The presence of colloidal tellurium in glass produces a colour tint which varies from blue to brown according to the size of the colloid particles, the blue glass containing larger particles than the brown.3 Polytellurides are present in some coloured glasses and impart a colour which is red or violet-red. 

The few compounds of tellurium with the elements sulphur, carbon and nitrogen which have been investigated, are described later (pp. 388-391). Most tellurium compounds are colourless, but the sulphur compounds, as well as the polytellurides, are in general dark red. A similar deepening of colour occurs in the polysulphides and polyselenides. 

Tellurium, potassium hydroxide, water, phenylacetylene, a trialkylmethylammonium chloride as phase-transfer catalyst, either tin(IJ) chloride or hydrazine hydrate as reducing agent and toluene as the organic solvent upon heating at approximately 100 for six hours produced Z,Z-bis[2-phenylvinyl ditellurium in low yields. Polytelluride radical anions were postulated as intermediates2 3. 

That the nature of the polytelluride solution plays an important role is also borne out by studies of the chromium-telluride system. If the polytel-lurides are prepared in situ by the reaction of elemental potassium with elemental tellurium in DMF, the products are considerably cleaner and can be obtained in higher yields than when the polytelluride source is a premade potassium salt, such as K2Te2 or K2Te3, It has been suggested that equilibria are occurring in the reaction flask. Pure Te2- and Te2- can be prepared in pure form in liquid ammonia, but there is no evidence for the formation of higher tellurides in the presence of alkali metal counter-... 

Cupric telluride, CuTe.—The telluride is stated to be formed by the action of tellurium-powder on a solution of cupric acetate in presence of sulphur dioxide.18 It can also be precipitated from a solution of sodium telluride, Na2Te a sesquitelluride, Cu2Te3, is obtained similarly from the polytelluride Na4Te3 (p. 130).14 A telluride of the formula Cu4Te3 occurs as the mineral rickardite. 

The propensity of tellurium to form intermolecular interactions distinguishes its chemical properties from those of sulfur and selenium for which such secondary bonding is virtually nonexistent (see Ref 38 and references therein). By contrast to polysulfides and polyseleiudes, polytelluride anions can exhibit charges that deviate from -2. 

The simple stoichiometry of the salts often obscmes the complexity found in many polytellurides, the stractures of which find few analogs in lighter chalcogen congeners sulfur and selenium. Spirocyclic Tev and Tes both show a square-planar tellurium atom (see Figure 7(a) and (b)). A similar motif is found in Rb2Tes that exhibits a continuous... 

A tellurium-containing borane without carbon atoms in the Te — B cage was obtained from B10H14 and sodium polytelluride. The telluraborane BioHjjTe was used for the preparation of cobalt, iron, platinum, rhodium, and iridium complexes, in which the TeBioHjo moiety served as the ligand. 

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. ... 

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