Mixed sulfur, selenium and tellurium

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. 

Pentahalides form essentially 1 1 adducts with sulfur, selenium, and tellurium donors, including phosphine sulfides and selenides. IR, Raman (see Raman Spectroscope, and NMR studies of the complexes formed with mixed-donor 0,S ligands showed bonding to occur via sulfur exclusively. The ionic [NbCl4()] -S2R2)][NbCle] complexes are volatile and act as a single-source precursor to mixed-Nb2 05/NbS2 films... 

Trisulfcdes and Triselenides, and Compounds with Mixed Three-Membered Sulfur-Selenium and Sulfur-Tellurium Chaim... 

Two acids with mixed three-membered chains are known, namely selenopentathionic and telluropentathionic acid. They are derived from pentathionic acid by substitution of selenium or tellurium for the middle sulfur atom of the latter, and behave in reactions with nucleophilic reagents as thiosulfates of divalent selenium and tellurium. The first salts of scleno-pentathionic (84) and telluropentathionic (85) acid were isolated in 1949, although the formation reactions in aqueous solutions had been known earlier. Wood (229) has by paper electrophoresis shown that the preparative methods lead to pure products. 

The one form of tellurium is silvery-white, semimetallic and isomorphous with gray Se. Like the latter it is virtually insoluble in all liquids except those with which it reacts. Gray Se and Te form a continuous range of solid solutions that appear to contain chains in which Se and Te atoms alternate more or less randomly. With sulfur, selenium can give mixed rings S Se8 n (n = 4-7).9... 

There are single examples of sulfur and selenium xanthates with the remaining structures to be described in this section featuring tellurium as the central element. There are a significant number of binary xanthates and, in common with these, their organotellurium xanthates feature extensive supra-molecular association, usually, but not exclusively, via Te- S secondary bond interactions. A rare example of mixed-ligand 1,1-dithiolate structure is available where the odd dithiolate ligand is a dithiocarbamate. 

---