Tellurium chain compounds

The subhalides of tellurium are an especially important class of solid state compounds, and they have been the subject of intensive studies, so that a rather complete picture of their chemistry and their properties has been obtained in recent years. Because of their high tellurium content they contain fragments of the homonuclear tellurium chains their modified tellurium structures are of great current interest with respect to possibly significant physical properties. Consequently, the results of various investigations on the synthesis of the compounds, on phase analysis by thermal methods, on crystal growth, on the structures, on spectroscopic, thermodynamic, optical, photoelectric, electrochemical properties have been reported in the last two decades. In a comprehensive review (237) all significant results are reported and discussed in detail so that the present chapter will be restricted to some selected and chemically important features. 

The largest number of selenium atoms in covalent selenium chain compounds isolated so far appears to be three, and even so, the representative compounds known are relatively few in number. In the case of tellurium, the maximum number is two. Rbeinboldt (191) has recently reviewed preparative methods for di- and triselenides, ditellurides, and compounds containing mixed sulfur-selenium and sulfur-tellurium chains. 

A new structure type is found for Ag2Hg(Se03)2. Both Ag+ and Hg2+ ions are in octahedral coordination in this compound.137 The polyhedra are linked by the pyramidal shaped selenite anions.138 In the crystal structure of the red tellurate Ag2Hg2(Te04)3, the tellurium atoms are in octahedral coordination of oxygen atoms, and the octahedra are linked to infinite chains running along the u-axis. 

Methyl and ethyl trifluoromethanesulfonates were used to alkylate dimethyl tellurium9,10. When a compound with two organotelluro groups linked by a chain of methylene groups is treated with methyliodide in acetone, both tellurium atoms are methylated11. 

The use of a more reduced telluride solution, namely, that of nominal composition Te2 with Cr(CO)6, yields an unusual cluster, [ Cr(CO)5 4Te2]2 (61) (Fig. 17), as the sole product, isolable as its (PPh4)+ salt. The tungsten and molybdenum analogs of this compound are not formed. The structure of the 61 dianion consists of a Te2 chain that is attached to four Cr(CO)5 groups, two on each tellurium atom. 

The limited solubility of long-chain alkyl halides in liquid ammonia makes it advantageous to evaporate the ammonia after the disodium telluride has formed and to dissolve the residue in an appropriate organic solvent. Ethanolic solutions of disodium telluride that had been prepared in liquid ammonia were used for the synthesis of the following heterocyclic tellurium compounds ... 

Some preliminary results on the electrochemical behaviour of elemental sulphur (and selenium) in AlCla-NaCl melts have been reported. The results for both elements were difficult to interpret, due in part to the low solubility of both elements in the melt and the modification of the electrode surfaces by the products of electrode reactions. In basic melts it was suggested that an cation is formed, in agreement with spectral studies. In acidic melts the results were more complex, and no exact conclusions could be drawn as to the nature of the species. A spectrophotometric study of the reactions of sulphur, selenium, and tellurium with aqueous solutions of NaOH at 150 °C (S, Se) and 300 °C (Te) has been carried out. From the experimental data the formation of the chain-like structure of polychalcogenide compounds was presumed. The spectra confirmed previous results concerning the mechanism of interaction of elemental chalcogens with aqueous NaOH solutions. 

The three methanesulfonyl derivatives, sulfur, selenium, and tellurium dimethanethiosulfonates, are isomorphous. Structure analyses have been carried out, starting with tellurium dimethanethiosulfonate and using tellurium as a heavy atom in the first stages. So far, the structure of the tellurium compound has been published in detail 128), and an electron density projection along the short crystal axis of the trisulfide (98) has shown the unbranched sulfur chain structure. 

Of the eight aromatic representatives, six crystallize in the same tetragonal trapezohedral space group and are isomorphous. These include all four p-toluenesulfonyl compounds, namely, the trisulfide, triselenide, and the two with mixed chains. The only ones which do not belong to the isomorphous series are dibenzenesulfonyl triselenide, which is tiiclinic, and tellurium dibenzenethiosulfonate which has one orthorhombic and one... 

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