Thiomolybdates preparation

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,... 

When hydrogen sulfide is passed into a strongly ammoniacal solution of copper(II) and molybdate(VI) ions, the initial copper-(II) sulfide precipitate is redissolved, the copper is reduced to the copper(I) state by sulfide ion, and the compound CuNH4MoS4, copper(I) ammonium thiomolybdate(VI), precipitates. The compound has been reported previously by Debray,1 who was unable to characterize it. The following method of preparation is based upon Debray s work and gives superior yields and higher purity. 

Recently, open-tipped MoS2 nanotubes were prepared by the decomposition of ball-milled ammonium thiomolybdate powder under a H2 + thiophene atmosphere, and used as a catalyst for the methanation of CO with H2.143 The conversion of CO to CH4 was achieved at a much lower temperature compared to polycrystalline MoS2 particles, and there was no deterioration even after 50 h of consecutive catalyzing cycles. This observation is of importance in the context of energy conversion of global C02. 

Oxo-thiomolybdates, [Mo04 S ] " n - 1-3), are prepared by the reaction of molybdate solutions with H2S under strictly controlled conditions of pH, temperature, and counterion. Excellent reviews of the syntheses and properties of these historically important four-coordinate tetrahedral species are available (174, 175). 

Of thef/iio-aciV/scorrespondhisfto the sulphides of molyhdemmi, two have been prepared, namely, hexathiomolybdic acid, HMoS . and per-thiomolybdic acid, H MoSj. The former has been obtained by decomposition of the ammonium salt with hydrochloric acid the latter is precipitated as a reddish-brown powder on the addition of dilute acetic acid to a solution of its potassium salt, KHM0S5.-... 

Thiomolybdates.—A large number of compounds have been described. Besides the normal salts, R, MoS4, basic compounds of the type Il giMogSg, and acid salts of the type R"S.3MoS3, have been prepared. Oxythiomolybdates, compounds intermediate between the molybdates and thiomolybdates, are also known. 

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. ... 

Sodium Thiomolybdates.—Two are knowm the normal salt, NajMoS, prepared as dark reddish crystals by the action of hydrogen sulphide upon a solution of sodium molybdate, and the acid salt, NagMogSy, obtained as a dark grey mass by treatment of the normal salt with a deficiency of acid. Oxythiomolybdates are obtained by the action of sodium hydrosulphide upon sodium tri- and para-molybdates. 

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 oxygen atoms of M04 can be replaced successively by sulfur, and all four thiometallates, MOsS ", M02S2 , MOSs " and MS4 have been prepared the thiomolybdates a century ago. They are useful reagents for the preparation of metal-sulfur clusters, and act as ligands, usually chelating but also as bridging groups. 

G.C. Stevens and T. Edmonds, Preparation and properties of thiomolybdate graphite catalysts, in Preparation of catalysts II (eds, B Delmon,... 

So far, two synthetic methods for the preparation of the di- -sulfido cysteinato complex have been reported (1) bubbling H2S gas into the di-/i-oxo complex, [Mo204(cys)2] , in water, (2) reduction of a one-to-one (1 1) mixture of thiomolybdate and molybdate by sodium dithionite, followed by the addition of the ligand. ... 

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. 

Spending thioamides in the best yields. Thiolysis of iminium salts derived from amides and oxalyl chloride or phosphoric trichlorides with ammonium tetra-thiomolybdate 40 occurs below room temperature within 2 h (Eq. 10) [32]. It is advantageous that the by-products are easily separated, although H2S is needed in order to prepare 40. 

The yellow-red thiomolybdates, [MoOj.S4 J (x = 0-3), are formed in the reactions of molybdate with H2S or other sulfiding agents in basic aqueous solutions.The complexes are formed in sequence (x = 3 2 —> 1 — 0), with very specific reaction conditions and cations required for the isolation (often in impure form) of intermediate complexes. The crystal structures of many thiomolybdate salts have been determined, wherein the discrete dianions exhibit distorted tetrahedral or tetrahedral (for [MoS4] ) geometries, with Mo=0 and Mo=S distances of ca. 1.76 and 2.20 A, respectively. Authoritative reviews of the synthesis, properties and coordination chemistry of these complexes have been prepared by Muller and coworkers. Other articles cover more recent advances and applications in this area. ... 

The complexity of the oxide-sulfide transformation leads to some difficulties in sulfiding, for example, tungsten sulfide or other sulfide phases if in interaction with a nonoptimized support. In this respect, the use of thiosalts and more particularly thiomolybdates and thiotungstates represents an interesting alternative to the classical sulfidation of oxides. Ammonium thiomolybdate (NH)2MoS4 (ATM) was first synthesized by Kruss [53] in 1884. Later, Alonso et al. described an improved way of preparing ATM [54]. The synthesis of ammonivun thiotungstate (ATT)... 

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