Synthesis Methods for Ce(CrO4)₂ · xH₂O and Crystal Structures of K₂CrSO₇, (NH₄)₂Cr₂O₇ and Na₂Cr₂O₇ · 2H₂O

New and quick methods to synthesize Ce(CrO₄)₂ · 2H₂O and Ce(CrO₄)₂ · H₂O, giving high yields, are described. The methods are based on exchange reactions by refluxing in water or on solid state reactions. The first crystal structure containing a chromatosulfato ion is presented. K₂CrSO₇ belongs to space group P2₁/n with a=7.4024(1), b=7.3908(1), c=12.9883(2) Å , β=90.021(1)^◦ and Z = 4. The CrSO₇²⁻ ion, consisting of one chromate group sharing one oxygen atom with one sulfate group, has a pseudo syn-C_2v conformation with eclipsed oxygen atoms. K₂CrSO₇ forms a three dimensional network of CrSO₇²⁻ ions held together by the charge balancing potassium ions, with the general structural features common with dichromate-like structures. The redetermination of the structures of (NH₄)₂Cr₂O₇ (space group C2/c, with hydrogen atoms located) and Na₂Cr₂O₇ · 2H₂O (space group P2₁, with hydrogen atoms located and the absolute structure established) are reported