Chemical elements
    Physical Properties
    Chemical Properties
      Molybdenum Hexafluoride
      Molybdenum Dichloride
      Molybdenum Trichloride
      Molybdenum Tetrachloride
      Molybdenum Pentachloride
      Molybdenum Oxychlorides
      Chlormolybdic Acids
      Molybdenum Dibromide
      Molybdenum Tribromide
      Molybdenum Tetrabromide
      Molybdenum Oxybromide
      Molybdenum Di-iodide
      Molybdenum Oxyiodide
      Iodomolybdic Acid
      Molybdenum Sesquioxide
      Molybdenum Dioxide
      Molybdenum Oxide Blue
      Molybdenum Trioxide
      Aluminium Molybdates
      Ammonium Molybdate
      Ammonium Dimolybdate
      Ammonium Paramolybdate
      Ammonium Trimolybdate
      Ammonium Tetramolybdate
      Ammonium Octamolybdate
      Barium Molybdates
      Barium Paramolybdate
      Barium Trimolybdate
      Barium Tetramolybdate
      Barium Octamolybdate
      Barium Nonamolybdate
      Beryllium Molybdate
      Bismuth Molybdates
      Cadmium Molybdates
      Caesium Molybdates
      Calcium Molybdate
      Calcium Trimolybdate
      Calcium Tetramolybdate
      Calcium Octamolybdate
      Chromium Molybdates
      Cobalt Molybdates
      Cobalt Dimolybdate
      Cobalt Trimolybdate
      Copper Molybdates
      Ferrous Molybdate
      Ferric Molybdate
      Indium Molybdate
      Lead Molybdates
      Lithium Molybdate
      Lithium Dimolybdate
      Lithium Paramolybdate
      Lithium Trimolybdate
      Lithium Tetramolybdate
      Magnesium Molybdates
      Magnesium Paramolybdate
      Magnesium Trimolybdate
      Manganese Molybdate
      Mercurous Molybdates
      Nickel Molybdates
      Potassium Molybdate
      Potassium Dimolybdate
      Potassium Paramolybdate
      Potassium Trimolybdate
      Potassium Tetramolybdate
      Potassium Octamolybdate
      Potassium Decamolybdate
      Rhodium Molybdates
      Rubidium Molybdate
      Rubidium Dimolybdate
      Rubidium Paramolybdate
      Rubidium Trimolybdate
      Rubidium Tetramolybdates
      Silver Molybdates
      Normal Silver Molybdate
      Sodium Molybdate
      Sodium Dimolybdate
      Sodium Paramolybdate
      Sodium Trimolybdate
      Sodium Tetramolybdate
      Sodium Iodomolybdate
      Strontium Molybdate
      Thallous Molybdate
      Thallous Paramolybdate
      Thallous Tetramolybdate
      Thorium Molybdate
      Uranium Molybdates
      Uranyl Octamolybdate
      Zinc Molybdates
      Zinc Trimolybdate
      Zinc Tetramolybdate
      Zinc Octamolybdate
      Zirconium Molybdate
      Permolybdic Acid
      Molybdenum Sesquisulphide
      Molybdenum Disulphide
      Dimolybdenum Pentasulphide
      Molybdenum Trisulphide
      Molybdenum Tetrasulphide
      Ammonium Thiomolybdates
      Ammonium Molybdosulphites
      Potassium Thiomolybdate
      Potassium Thiodimolybdate
      Potassium Dithiodioxymolybdate
      Potassium Molybdosulphite
      Sodium Thiomolybdates
      Sodium Molybdosulphites
      Molybdenum Sulphates
      Molybdenum Selenide
      Complex Molybdoselenites
      Chromates of Molybdenum
      Molybdenum Phosphide
      Molybdic Metaphosphate
      Heteropoly-compounds with Phosphorus
      12-Molybdophosphoric Acid
      9-Molybdophosphoric Acid
      172-Molybdophosphoric Acid
      Molybdenum Carbides
      Molybdenum Carbonyl
      Reddish-violet Salts
      Yellow Salts
      Thiocyanates of Molybdenum
      Molybdenum Monosilicide
      Molybdenum Sesquisilicide
      Molybdenum Disilicide
      Molybdosilicic Acid and Molybdosilicates
      12-Molybdosilicic Acid
    PDB 1aa6-1qh8
    PDB 1r27-2jir
    PDB 2min-3unc
    PDB 3uni-4f6t

Molybdenum Dichloride, MoCl2

The normal chloride of divalent molybdenum, MoCl2, which in solution would yield the simple ions Mo•• and Cl', is not known. The so-called " molybdenum dichloride," which does contain the divalent metal, has been shown to be an amphoteric compound of more complex composition. It may be prepared by heating to redness the trichloride in a stream of dry carbon dioxide, when the volatile tetrachloride distils, leaving a residue of the dichloride. Careful regulation of the temperature, and exclusion of air and moisture, are important, or the product will contain higher chlorides and oxychlorides. The dichloride is also formed by heating molybdenum with mercurous chloride, or by passing chlorine largely diluted with carbon dioxide over the moderately heated metal; in both cases satisfactory yields are difficult to obtain. The most productive method appears to be the heating of molybdenum powder in a stream of carbonyl chloride at 610° to 620° C. The dichloride remains as a heavy yellow powder, which may be extracted with ether containing 5 per cent, of absolute alcohol. After evaporation of the solution in vacuo, a light yellow stable powder, of composition Mo3Cl6.C2H5OH, remains, the alcohol in which cannot be removed by heating in an inert atmosphere without further decomposition taking place. The addition of alcoholic silver nitrate to a solution of the compound in alcohol precipitates silver chloride, and the mother-liquor on standing deposits the compound Mo3Cl4(NO3)2.C2H5OH; immediate treatment of the mother-liquor with ether, however, causes separation of the alcohol-free compound Mo3Cl4(NO3)2. The formula for the chloride may therefore be written (Mo3Cl4)Cl2.

If the original dichloride powder is extracted with concentrated hydrochloric acid, long yellow needles, of composition Mo3Cl6.HCl.4H2O, may be separated almost quantitatively from the solution. These in air lose hydrogen chloride, becoming green; when heated in a stream of hydrogen chloride the compound Mo3Cl6.H2O results. The yellow crystalline substance acts as a chloracid containing the anion Mo3Cl7', its solution in the minimum quantity of hydrochloric acid yielding, with concentrated solutions of metallic chlorides, salts of composition R[Mo3Cl7].xH2O. The addition of dilute acid to a solution of the chloracid in dilute alkali precipitates a crystalline hydroxide of composition [Mo3Cl4.2H2O](OH)2.6H2O. This formula is based on the behaviour of the compound on dehydration; at 100° C. 6 molecules of water are lost, a seventh is expelled below 300° C., and the final product, which resists further dehydration, has the composition [Mo3Cl4.2H2O]O. With hydrobromic acid the hydroxide yields acids for which the following formulae have been given: H[Mo3Cl4Br3.H2O]. 3H2O and H2[Mo3Cl4Br4.4H2O]2H2O; salts of these acids have also been described.

Molybdenum "dichloride," that is, the chloracid HMo3Cl7.4H2O, dissolves in aqueous alkali hydroxides forming yellow solutions which, on boiling, deposit the black dihydroxide Mo(OH)2. The alcoholic solution conducts electricity, the molecular conductivity increasing on dilution; hydrogen, the oxychloride Mo3Cl4(OH)2, and sometimes molybdenum are liberated at the cathode, whilst acetaldehyde and ethyl chloride are formed at the anode.

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