Oxychlorides

Several oxychlorides of chromium said to possess definite formulae, for example, Cr₂Cl₅O.4H₂O, Cr₂Cl₄(OH)₂, Cr₂Cl₆.Cr₂O₃, Cr₂Cl₂(OH)₄, Cr₂Cl(OH)₅, Cr₂O₃.8CrCl₃.24H₂O, Cr₂O₃.4CrCl₃.9H₂O, 2Cr₂O₃.2CrCl₃, and CrOCl.3H₂O, have been described, but possibly some of them are merely physical mixtures. Basic chromium chlorochromate, Cr₃O₆Cl₂, is known, and two compounds, (CrO₂)₅Cl₆ and Cr₆O₉Cl₄, obtained by the action of nitric oxide, or, in sunlight, of carbon monoxide upon chromyl chloride, CrO₂Cl₂, have been prepared. The former, (CrO₂)₅Cl₆, which possesses chlorinating and oxidising properties, forms brown deliquescent crystals, and decomposes on heating to 150° C. into chromyl chloride, or, if heated rapidly, into chlorine, and Cr₃O₆Cl₂, which remains as a solid residue. Above 180° C. it yields oxygen and a brownish-black residue of Cr₆O₉Cl₄. The oxychloride, Cr₂OCl₄, is obtained by the action of hydrochloric acid on the hydroxide, Cr₂O(OH)₄. Another, of the formula CrOCl₃, in which chromium appears to be pentavalent, forms double salts with the chlorides of the alkali metals and of certain organic bases. For instance, CrOCl₃.2KCl is obtained as a red precipitate by treating with hydrogen chloride a mixture of a solution of potassium chloride and a concentrated solution of chromic acid already saturated with hydrogen chloride, and the mixture maintained at a low temperature. A compound, Cr₂O₅Cl₂, is described as resulting from the heating of chromyl chloride with chromic anhydride in a sealed tube.