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Is it possible to synthesise such a salt as chromium (III) chromate/dichromate? The intended formulas are $\ce{Cr2(CrO4)3}$ and $\ce{Cr2(Cr2O7)3}$ and they feature both trivalent and hexavalent chromium. However, heating a mixture of chromium (III) oxide and chromium (VI) oxide seems to just produce chromium (IV) oxide and oxygen instead:

$\ce{Cr2O3 + 3CrO3 -> 5CrO2 + O2}$

There is a compound $\ce{Fe4[Fe(CN)6]3}$ which is a salt featuring trivalent iron in the cation, and divalent iron in the anion. Therefore, why not a salt featuring trivalent chromium in the cation, and hexavalent chromium in the anion?

How would chromium (III) chromate's properties differ from other "ordinary" chromates?

Search engines don't find any useful results for chromium chromate, but I suspect that to be the idiosyncratic trouble with the search engine itself (it just returns a list of various chromate salts, and doesn't seem to understand that both the "chromium" and "chromate" parts are supposed to be found in the single compound). I don't consider those results: [1], [2] to be useful, as they don't seem to have been human-generated and they contain no useful information.

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You're assumption is correct, chromic chromate, $\ce{Cr2(CrO4)3}$ does exist. Some other names listed at NIH.gov are chromium(III) chromate and dichromium tris(chromate), and the diagram below is from there.

Chromic Chromate

As one would expect, it's a strong oxidizer and an environmental health hazard. See more at Haz-Map for more information.

Chromic chromate, $\ce{Cr2(Cr2O7)3}$, as shown at EndMemo, might exist, or might be present as a complex species in solution. It is mentioned in these papers on chromium plating by C. Kasper and by J. P. Hoare.

See also N. V. Mandich's paper on chromium chemistry.

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  • $\begingroup$ I don't think this compound was ever synthesized or possibly be ever synthesized. $\endgroup$ Apr 3 at 2:55
  • $\begingroup$ @NilayGhosh, which compound? Cr2(CrO4)3 exists, but there are papers on the dichromate quoted above, but existing only in solution. $\endgroup$ Apr 3 at 13:43

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