Molybdenum Oxide Hydrates
Solid compounds of molybdenum containing hydrogen and oxygen exist with Mo in each of the oxidation states 3 through 6. In addition, mixed-valence compounds containing Mo in the formal oxidation state 4.8 and 5.5 to 5.86 have been described. These compoun
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The Mo-O system and the anhydrous molybdenum ox ides can be found in the volume " Molybdän" Erg.-Bd. B 1, 1975, pp. 21/144. The anhydrous molybdates with Sb to Cs (System Nos. 18 to 25) are described in "Molybdän " Erg.-Bd . B 1, 1975, pp. 145/241, those with Be to Cr (System Nos. 26 to 52) in " Molybdän" Erg.-Bd. B 2,1976. The hydrous molybdates with Sb to Cr (System Nos. 18 to 52) can be found in " Molybdenum" Suppl. Vol. B 4,1985.
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Molybdenum Oxide Hydrates Older data are given in " Molybdän" , 1935, pp. 102/13.
Overview
Solid compounds of molybdenum containing hydrogen and oxygen exist with Mo in each of the oxidation states 3 through 6. In addition , mixed-valence compounds containing Mo in the formal oxidation state 4.8 and 5.5 to 5.86 have been descr ibed . These compounds are generalizing designated as oxide hydrates but in some cases mayaIso be formulated as hydroxides or hydroxide oxides. " Molybdic acids " do not exist in the solid state . The compounds Mo03· n Hp with n = 1 and 2 have clearly been identified as oxlde hydrates although the term " molybd ic acid" is used even in recent papers .
A gaseous hydroxide oxide of MOVI was detected at high temperatures. For MOVI the format ion of a crystalline peroxo compound has been reported. For formal reasons the hydrogen insertion compounds, HxMo03 (0< X < 2), are also described in this sect ion . These compounds, wh ich are obtained by the introduction of hydrogen into Mo03, are termed " bronzes" in the literature. There is stilllittle knowledge about the exact equi librium location of the hydrogen in the Mo0 3 host structure, the amount of charge transfer, the mobility, and the bonding properties. Recent papers (up to 1985) dealing with these subjects have been considered. Details of the formation and properties of the hydrogen tungsten oxide bronzes can be found in " Wolf ram" Erg.-Bd. B 3, 1979, pp . 31/9.
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Mo(OHh
In the literature this compound is usually designated as Mo(OHh but the formulat ion MOP3'3HP can also be found . Mo(OHh is precipitated during the electrolytic reduction of Na2Mo04 (0.025 M) in weakly acidic solutions (e. g., 0.01 to 0.03 N HCI or H2S04) (1) or of ammon ium molybdate solution (2). From brown MOIII solutions, produced by electrolytic reduction of molybdate(VI) in 0.5 to 3N HCI, the Mo(OHh was precipitated by dilution [3). A dense deposit of M0 203· n Hp was obta ined on a Ni-plated dull electrode in an ammon ia electrolyte at 4.5 V and 40 to 50°C. After 5 min drying at 160°C the number of Hp molecules, n, is 3. Optimum conditions for the electrogravimetric determination of Mo as M0 203·3Hp are given in the paper [4]. Anhydrous molybdenum(lII) ox ide, prepared by the reduction of Mo0 3with K in liquid NH3 at -33SC, was converted to M0 203·3Hp by agitation with H20 at 23°C for 15 min . The insoluble black solid was dried in vacuum over concentrated sulfuric acid [2]. Gmelin Handboo k Mo Suppl. Vol. B 3
K.-H. Tytko, Mo Molybdenum © Springer-Verlag Berlin Heidelberg 1986
Oxide Hydrates
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A black precip
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