Synthesis and crystal structure of Ge(SO4)(2)

Colourless single crystals of Ge(SO4)(2) were obtained as single phase products from the binary oxides GeO2 and SO3. The reaction was carried out in a silica glass ampule enclosed in an autoclave at 350 degrees C. Ge(SO4)(2) forms a layer structure with corner-linked GeO6 octahedra and SO4 tetrahedra. The crystal structure (R3? c, Z=6, a=4.622 angstrom, c=42.576 angstrom) belongs to the Ni(ClO4)(2)-type. The SO4 tetrahedra are rotated by 24 degrees. The sense of rotation alternates between adjacent layers. This rotation is connected to a super structure with a doubled c-axis and a disorder between the layers according to the sense of rotation. Ge(SO4)(2) is one of the very rare examples of a sulphate of a tetravalent cation and is the representative with the smallest ionic radius. Lattice energy calculations confirm the electrostatic consistency. Vibrational spectra were recorded and show the typical features of GeO6 and SO4 units.