Tellurium compounds complexes

A number of selenium and tellurium compounds of the presently discussed metals show a quite different behavior from the Fe-S system. Iron and selenium form two compounds FeSe with a broad stoichiometry range and FeSe2 with a much narrower composition field. Below 400 the non-stoichiometric Fei xSe exists by creation of iron vacancies and can have compositions lying between FeySes and Fe3Se4. At low temperatures there exist two phases an a (PbO type) and a f) (NiAs type) phase. The crystal sUiicture of the diselenide, FeSe2, is an orthorhombic, C18 (marcasite) type. In the Fe-Te system, the defect NiAs structure is found at a composition close to FeTei.s, as about one-third of the Fe atoms are missing. At compositions around FeTe the behavior is complex, and the f)-phase has the PbO structure (like FeSe) but with additional metal atoms (i.e., FeuTe). 

Multicomponent reactions (MCRs) have been known to produce highly complex and diverse structures [76]. There is a considerable interest in the application of new multicomponent reactions to access biologically relevant molecules [77,78] and natural products [79]. A recent report has disclosed multicomponent Passerini and Ugi reactions to produce, rapid and efficiently, a library of redox-active selenium and tellurium compounds [80]. The compounds showed promising cytotoxicity against several cancer cell lines. 

The mechanism of tellurium resistance has been investigated using genetic manipulation similar to that of Se (see above) and cellular oxidant capacity apparently plays an important role.144,206 A few tellurite determinants - both chromosomal and plasmid encoded - have been identified in bacte-ria.113,147 192 207 208 Recent studies have focused on the role of methyltransf-erases in Te resistance. Liu et a/.111 determined that the E. coli gene tehB uses S-adenosyl methionine and a methyltransferase in tellurite detoxification, but while no methylated tellurium compounds (see below) were observed, a loss of tellurite was observed in tellurite-amended cultures and Te complexation was inferred.191... 

The ligand chemistry of heterocyclic tellurium compounds has been examined over several years.85 86-92 104-106 The study105 of the monomeric (6) and dimeric (7) complexes, which were obtained from the reaction of Na2PdCl4 and tellurophene and separated by their solubility differences in acetone and chloroform, is illustrative of the preparative chemistry and characterization techniques used in this area of chemistry. 

Salts of the metals are thus present in equilibrium with the violet tellurium compounds, and in the case of the dibisulphate the balance is controlled by the proportion of wrater present. This is rendered visible in the action of iron upon phenoxtellurine dibisulphate, for the violet mixture becomes red when dried on clay in a desiccator, but the violet colour is restored on exposure to moist air. The method of examining a coloured complex consists in treating it with water, when the acceptor 55 is set free and can be extracted by ether the residual salt can then be reduced by adding potassium bisulphite, and the nucleus of the donor again extracted by ether. The products are insoluble in water, so that fresh equilibria cannot presumably be set up. 

With bis[triethylstannyl] tellurium, a 2 1 (ligand cadmium compound) complex (dec. > 80°) was obtained in 47% yield1. 

Aryl triphenylstannyl tellurium reacted with 1,5-cyclooctadienedichloropalladium in chloroform at 20°. With equimolar amounts of the reagents 1,5-cyclooctadienechloro (arenetellurolato)palladiums were isolated with 2 moles of tellurium compound per mole of palladium complex, 1,5-cyclooctadiene bis[arenetellurolato]palladiums were obtained2. 

Tellurium Compound Metal Compound Conditions Complex Refer- ence... 

Most of the complexes have well defined melting points. They appear to be monomeric in solution . An interesting method for the preparation of thiazolidine-2-thione complexes of aryl tellurium trichlorides is the addition of the tellurium compound to a melt of the ligand kept at 110°. Complexes with 1 1, 1 2, and 1 4 stoichiometries (Te-compound ligand) were obtained after recrystallization from dry methanol. Phenyl tellurium trichloride complexes with thiourea appear to form only when an organic solvent is used as the reaction medium in aqueous media the trichloride is reduced to the monochloride that is isolated as the thiourea adduct . 

Dicyclohexyl tellurium dibromide formed complexes with pyridine, piperidine, mor-phohne, diethylamine, 4-bromoaniline, dimethylformamide, and dimethyl sulfoxide. The complexes have two molecules of ligand per molecule of tellurium compound . Bis[benzoylmethyl] tellurium dibromide formed 1 2 complexes with cyclic amines. ... 

The methods of determining Te with the use of basic dyes are very sensitive. The tellurium bromide complex has been extracted as the ion-associate with Butylrhodamine B [44,45] or Victoria Blue 4R (e = 8.0-10 ) [46]. The halide complexes give also ion-associates, extractable into toluene (e = 3.75-10 ) with Violet Red [47 9]. The TeBr associate with Rhodamine 6G can be floated with benzene, and the separated compound is then dissolved in a mixture of benzene with ethanol (e = 1.7-10 ) [50]. The ion-associate of the iodide complex of Te(IV) with Nile Blue A has been floated with cyclohexane, and the separated compound dissolved in methanol (e = 1.4-10 at 640 nm) [51]. High sensitivity has... 

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