Molybdenum thiomolybdates

Of the many molybdenum sulfides which have been reported, only MoS, M0S2 and M02S3 are well established. A hydrated form of the trisulfide of somewhat variable composition is precipitated from aqueous molybdate solutions by H2S in classical analytical separations of molybdenum, but it is best prepared by thermal decomposition of the thiomolybdate, (NH4)2MoS4. MoS is formed by heating the calculated amounts of Mo and S in an evacuated tube. The black M0S2, however, is the most stable sulfide and, besides being the principal ore of Mo,... 

In terrestrial vegetation, molybdenum and sulfur interfere with copper-induced deficiencies (Gupta 1979). Copper poisoning in cattle and other ruminants is governed by dietary concentrations of molybdenum and sulfate (Lewis et al. 1967 Todd 1969 Buckley and Tait 1981 Eisler 1989). Molybdenum and sulfur in mammalian diets cause a decrease in the availability of copper because of the formation of the biologically unavailable copper-thiomolybdate complex (Aaseth and Norseth 1986). Cattle die when grazing for extended periods on pastures where the ratio of copper to molybdenum... 

Suttle, N.F. 1980. The role of thiomolybdates in the nutritional interactions of copper, molybdenum, and sulfur fact or fantasy Ann. N.Y. Acad. Sci. 355 195-207. 

Suttle, N.F. and A.C. Field. 1983. Effects of dietary supplements of thiomolybdates on copper and molybdenum metabolism in sheep. Jour Comp. Pathol. 93 379-389. 

A second example of cluster formation involves the antagonism between molybdenum and copper. The presence of high concentrations of molybdenum in pasture soils is known to lead to symptoms of copper deficiency in animals. This has been attributed to the formation of thiomolyb-dates in the rumen of grazing animals, which then interfere with the metabolism of copper through the formation of cluster compounds of molybdenum and copper. It has been shown that thiomolyb-date, MoS42, readily forms such clusters on reaction with phosphines and copper(II) salts under appropriate conditions. Structures are shown in Figure 38.992,993 Reaction between thiomolybdate and copper compounds in aqueous solution have also been reported.994... 

The trisulphide M0S3 is precipitated when hydrogen sulphide is passed through weakly acid solutions of molybdates, or can be obtained by thermal decomposition of thiomolybdates, but it has also been identified in Chilean ores. It decomposes on heating above 1000°C to give free sulphur and molybdenum disulphide. 

Potassium Thiomolybdate, K2M0S4, is prepared, according to Berzelius loc. cit.), by gradually heating to bright redness a mixture of molybdenum disulphide, potassium carbonate, sulphur, and a little powdered charcoal. The water solution of the cold black melt is dark red in colour, and on gentle evaporation yields erj stals which may be further purified by precipitation of their aqueous solution with alcohol. The substance is not entirely stable. ... 

The reaction is completed after one hour at pH 10 and a temperature of 80-85 °C. The addition of sulfuric acid to change the pH to 2.5-3.0 converts the thiomolybdate to insoluble molybdenum trisuliide. 

Molybdenum Removal by Adsorption on Activated Carbon [5.34]. The principle of the method is the selective adsorption of thiomolybdate by activated carbon while tungstate will not be retained. 

In a series column operation, thiomolybdate is sorbed in the first column (resin 930) and tungstate in the second (resin 937). The molybdenum removal is better than 99%. The impiffity to WO3 ratios are ... 

Ammonium oxymolybdenum complexes with amines These complexes are prepared by the acid/base reaction of an acidic molybdenum source such as molybdenum trioxide, molybdic acid, ammonium molybdate [41] and ammonium thiomolybdates with oil-soluble amines [42], The preferred aminic compounds are lubricant additives known as dispersants, examples being succinimides and Mannich-type bases, as in Reactions (4.42) and (4.43) [41] ... 

The endemic disease is characterized by severe scouring and impaired condition in cattle. Molybdenum exposure leads to copper depletion and in turn secondary copper deficiency hence, the copper and sulfur supply of animals is of major importance. Inorganic molybdenum compounds, in the presence of sulfite, are converted to thiomolybdates (e.g., tetrathiomolybdate MoS ) by microorganisms in the rumen. The thiomolybdates then react rapidly with particulate matter and proteins to form complexes that bind copper strongly. Bioassays... 

The thiomolybdate(VI) anions [MoO S4 ] (n = 0-3) have been prepared by a number of methods and, with the exception of [MoOsS] ", act as versatile ligands to a wide variety of metal ions (see Table 1). In each of the compounds listed in this table, the [MoO S4- p ion acts as a bidentate ligand to the metal and the resultant structural versatility has been clearly demonstrated for copper(I) (Table 2). In addition, thiomolybdate(VI) anions are of interest since they have special relevance to aspects of bioinorganic chemistry. Thus, [MoS4] has been widely used in the synthesis of Fe—Mo—S clusters, examples of which serve as spectroscopic analogues for the iron-molybdenum cofactor of the nitrogenases (see Section 36.6.2), and Cu—Mo—S aggregates, which are relevant to the copper deficiency induced by molybdenum in ruminant animals. 

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