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Chromium Silicofluoride, Cr2F6.(SiF4)3

Chromium Silicofluoride, Cr2F6.(SiF4)3, is obtained in solution when chromium sesquioxide is dissolved in hydrofluosilicic acid.6 It has not yet been isolated, since in aqueous solution it undergoes decomposition; the violet solution spontaneously and gradually becomes bluish green, and silicon tetrafluoride is liberated, thus:

Cr2F6.(SiF4)3 = SiF4 + Cr2F6.(SiF4)2,

the silicon tetrafluoride then being decomposed by water. On evaporation more silicon tetrafluoride is liberated, and a green hydrated fluoride can be isolated, to which Recoura gives the formula (CrF.5H2O)SiF6, considering it analogous to the two silicofluorides prepared by Jorgensen, of composition (CrCl.5NH3)SiF6 and (CrCl.4NH3.H2O)SiF6.

The freshly prepared violet solution of chromium silicofluoride reacts with potassium chloride, thus:

Cr2F6.(SiF4)3 + 6KCl = 3K2SiF6 + 2CrCl3;

but if the solution has been allowed to stand, the products are potassium silicofluoride and a compound, (Cr2F2)Cl4, from which the fluorine cannot be precipitated by adding barium chloride.

The hydrated compound (CrF.5H2O)SiF6 is stable in dry air or in a vacuum; but in contact with moist air it slowly loses silicon tetra- fluoride, and ultimately yields hydrated chromic fluoride, Cr2F6.7H2O.

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