Crystal Structures of the Selenate Alums CsM[SeO4]2.12H2O (M = Al, Cr, Fe, Rh or In)

Structure determinations ofthe alums CsM[SeO4]2.12H2O have been carried out for M =aluminium(III), chromium(III), iron(III), rhodium(III) and indium(III). Structures of the cubic crystals, space group Pa3, were determined at 295(1) K. For Al, Cr, Fe, Rh and In, respectively, crystals with a = 12.544(3), 12.575(3), 12.615(5), 12.532(7) and 12.694(6)? gave 568, 561, 556, 566 and 269 independent reflections which refined to R = 0.040, 0.041, 0.051, 0.031 and 0.027. The compounds belong to the a alum structural class, in contrast to the caesium sulfate alums of aluminium, chromium, iron and indium, which have the ß alum structure. This difference between the a and ß alum structures does not affect the MIII-O bond length.