Molybdenum and Tungsten Compounds

Molybdic and Tungstic Anhydrides. Place several ammonium molybdate crystals onto the lid of a crucible and first heat them carefully, and then roast them strongly. What occurs Perform a similar experiment with ammonium tungstate or tungstic acid. Write the equations of the reactions. At what temperature do molybdic and tungstic anhydrides sublime  

Compare the properties of the trioxides of the chromium subgroup elements (their colour, thermal stability, oxidizing ability, and reaction with water). 

Molybdic and Tungstic Acids. What hydrates do molybdenum and tungsten trioxides form  

Pour 2-3 ml of a 10 % nitric acid solution into 2-3 ml of a 20 % ammonium molybdate solution. What substance precipitates What is its colour Wash the precipitate with water by decantation and divide it into two parts. React one part of the precipitate with an excess of concentrated hydrochloric acid and the other with a 20% sodium hydroxide solution. Explain the results. Write the equations of the reactions. Under what conditions does molybde-num(Vl) oxide dihydrate form  

Prepare a solution of sodium tungstate containing 0.5 g of the dry salt, and pour into it an equal volume of a 10% hydrochloric acid solution. Wash the precipitate by decantation with water slightly acidified with hydrochloric acid. 

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Yoshimura, T., K. Tsunoda, and K. Nishimoto. 1987. Effect of molybdenum and tungsten compounds on the survival of Coptotermesformosanus Shiraki (Isoptera Rhinotermitidae) in laboratory experiments. Mater. Org. (Berl.) 22 47-56. 

Salts of Molybdic and Tungstic Acids. What types of salts of molybdic and tungstic acids exist Give examples of isopoly- and heteropoly molybdenum and tungsten compounds. What is the composition of para- and metamolybdates and of para- and metatungstates Which molybdates and tungstates dissolve poorly in water ... 

The fundamental vibrations have been assigned for the M-H-M backbone of HM COho, M = Cr, Mo, and W. When it is observable, the asymmetric M-H-M stretch occurs around 1700 cm-1 in low temperature ir spectra. One or possibly two deformation modes occur around 850 cm l in conjunction with overtones that are enhanced in intensity by Fermi resonance. The symmetric stretch, which involves predominantly metal motion, is expected below 150 cm l. For the molybdenum and tungsten compounds, this band is obscured by other low frequency features. Vibrational spectroscopic evidence is presented for a bent Cr-H-Cr array in [PPN][(OC)5Cr-H-Cr(CO)5], This structural inference is a good example of the way in which vibrational data can supplement diffraction data in the structural analysis of disordered systems. Implications of the bent Cr-H-Cr array are discussed in terms of a simple bonding model which involves a balance between nuclear repulsion, M-M overlap, and M-H overlap. The literature on M-H -M frequencies is summarized. 

The complexes [W2CI4L4] undergo a reversible one-electron oxidation. A comparison of the oxidation potential of analogous molybdenum and tungsten compounds clearly shows that the tungsten compounds are considerably easier to oxidize. This ease of oxidation is believed to be responsible for the fact that it is difficult, if not impossible, to obtain quadruply bonded tungsten compounds by synthetic procedures which are known for molybdenum.339... 

Molybdenum and tungsten compounds have long been known to catalyze the transformations of alkenes into epoxides and diols by hydrogen peroxide.171"173 This reaction was found to be suitable for the epoxidation of water-soluble alkenes such as allylic alcohols (equation 30)174,175 or unsaturated carboxylic acids (equation 31).171 Tungsten catalysts were found to be more active and selective in aqueous solution than molybdenum complexes. 

THE HYDROLYSIS OF 4-PYRIDIOMETHYL-MANGANESE, -MOLYBDENUM, AND -TUNGSTEN COMPOUNDS... 

M. L. H. Green, Studies on Synthesis, Mechanism and Reactivity of Some Organo— Molybdenum and -Tungsten Compounds, Pure Appl. Chem. 50, 27-35 (1978). 

Also. J. B. Pedley, ed., Computer Analysis of Thermochemical Data (CATCH Tables)." Univ. of Sussex, Brighton, 1972. (i) Halogen compounds (1972), (ii) nitrogen compounds (1972), (iii) phosphorus compounds (1972), (iv) silicon compounds (1972), (v) chromium, molybdenum, and tungsten compounds (1974). Booklets (iv), (v) give data on organometallic compounds. The book by Cox and Pilcher (A149) is to be updated under the same system. 

The first known r -dihydrogen complexes, so-called non-classical hydrido complexes, were the molybdenum and tungsten compounds, M(CO)3(PR3)2(ti -H2) (M = Mo, W R = /-Pr) isolated for the first time by Kubas [35]. In order for the... 

Molybdenum and tungsten compounds are usually iso-morphous and essentially isodimensional. 

Brill WJ, Eia SW and Breznak JA (1987) Termite killing by molybdenum and tungsten compounds. Naturwissenschaften 74 494-495. 

Of direct relevance to this work are various other reviews that cover the chemistry of Mo/S complexes (9, 10), the anions (if), the S ligand (12), and the sulfur-bridged molybdenum and tungsten compounds (13). 

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