Tellurides halides

Fig. 3. Tellurium helices in copper telluride halides. (Redrawn from J. Fenner and H. Schulz, Acta Cryst. B35, 307 (1979), Fig. 2, p. 311.)...

Fig. 4. Spectral reflectance measurements in copper telluride halides. (Redrawn from A. Rabenau, H. Rau, and G. Rosenstein, Solid State Commun. 7, 1281 (1969), Fig. 1,...

Gold telluride iodide, AuTczI, was the first example of a gold chalco-genide halide, and was found in 1969 (305). Systematic investigations confirmed the existence of at least six compounds four telluride halides and two selenide halides (see Table IV). No sulfide halides have been reported. 

The telluride halides crystallize in monoclinic lattices, but only In-TeBr and InTel are isotypic 162). InTeCl forms a layer type of structure, as do InSCl and its analogs, but, owing to the size of the Te atom and the enhanced covalency of the In-Te bond, only a coordination number of 4 for indium is realized. The structure is built up of strongly distorted, InTesraCli/j tetrahedra that share the corners and edges occupied by Te atoms. The Cl atoms are coordinated to one tetrahedron each, and do not take part in the layer formation 324, 325). 

Tellurium forms inorganic compounds very similar to those of sulfur and selenium. The most important tellurium compounds are the tellurides, halides, oxides, and oxyacids (5). Techniques and methods of preparation are given in the literature (51,52). The chemical relations of tellurium compounds are illustrated in Figure 2 (53). 

Selenides and tellurides Halides and oxohalides Oxides and oxoacids Compounds with nitrogen Aqueous solution chemistry... 

Dialkyl tellurides (general procedure).Te powder (3.58 g, 28 mmol), Na chips (1.29 g, 56 mmol), and naphthalene (0.72 g, 5.6 mmol) in THF (25 mL) are refluxed under N2 and stirred for 3 h. The heterogeneous white mixture is cooled at 0°C and the alkyl halide (56 mmol) is added slowly, stirring for 30 min. After 30 min of additional stirring, the mixture is filtered, the solution evaporated and the residue distilled under vacuum, giving the telluride. 

The use of sodium dithionite (Na2S204) and thiourea dioxide (TUDO HN=C(NH2)S(0)0H) has been introduced later as a reducing agent for the preparation of sodium telluride in an aqueous medium, followed by reaction with n-alkyl halides to give dialkyl teUiirides. - ... 

Dialkyl tellurides (general procedure) A mixture of TUDO (0.2 g, 2 mmol), NaOH (0.112 g, 2.6 mmol), Te powder (0.128 g, 1 mmol) in H2O (0.75 mL) and THF (0.75 ml) is refluxed for 1 h. The alkyl halide (2 mmol) and (cetyl trimethyl ammonium bromide) CTBA (0.004 g, 1.1 X 10 mmol) in THF (0.5 mL) are added to the pale pink solution. After 1 h of additional reflux the mixture is worked up in the usual manner and the residue purified by column chromatography on Si02 (elution with petroleum ether 40-60°C). 

The title reagent (prepared by the reaction of sodium hydrogen telluride with chlorotriph-enylstannane) reacts easily with the more active halides such as benzyl bromides whereas common halides need to be activated by cesium fluoride. 

Dialkyl tellurides (general procedure) Bis(triphenylstannyl) telluride (1 equiv), alkyl halide (2 equiv), excess CsF (4 equiv) and the solvent (MeCN or MeCN/THF) are mixed, kept nnder N2 and monitored by thin layer chromatography (TLC) (or NMR). Usual work-up of the mixture yields the telluride. 

From sodium telluride and non-activated aryl halides... 

The normal low reactivity of aryl halides towards nucleophilic reagents is not generally observed in their reaction with alkali tellurides. The observed reactivity seems to be... 

Alkyl phenyl tellurides (general procedure) Li metal (1.4 g, 0.2 mol) in small pieces is added under N2 to a solution of diphenyl ditelluride (4.1 g, 10 mmol) in dry THF (100 mL). The mixture is stirred at room temperature for 6 h, unreacted lithium is removed using a spatula and the aUcyl halide (20 mmol) neat or in THF is added dropwise to the stirred yellowish-brown solution. The solution is stirred at room temperature for 30 min, and under reflux for an additional 30 min. The solvent is evaporated, and HjO (10 mL) and ether (25 mL) are added to the residue, mixing thoroughly. The ethereal phase is separated and evaporated. The residue is fractionally distilled under vacuum (yields 62-79%). 

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