Phase transitions and twinned low-temperature structures of tetra­ethyl­ammonium tetra­chlorido­ferrate(III)

At room temperature, tetra­ethyl­ammonium tetra­chlorido­ferrate(III) has a disordered structure in the high-hexa­gonal space group P6₃mc. At 230 K, the structure is merohedrally twinned in the low-hexa­gonal space group P6₃. At 170 and 110 K, the structure is identical in the ortho­rhom­bic space group Pca2₁ and twinned by reticular pseudomerohedry. All three space groups are polar and the direction of the polar axis is not affected by the twinning.