THE SUPERSTRUCTURE OF K3HGE7O16.4H2O

Potassium germanate K3HGe7O16 . xH2O (x almost-equal-to 4) forms a cubic body-centered superstructure with a = 15.418(8) angstrom at room temperature. A single-crystal refinement of the average structure with a(A) = 1/2 a in space group P43mBAR converged to R = 0.077. For the superstructure with eight formula units per unit cell, a model in space group I23, based on two types of twin domains related by a pseudo-mirror plane, was obtained. The relative intensities of the overlapping twin reflections were allocated according to the calculated intensities. The refinement in overall temperature factor mode converged to R = 0.090 for reflections with F0 > 3-sigma(F0) and R = 0.175 for the superstructure reflections. The structure is a three-dimensional framework of GeO6 octahedra and GeO4 tetrahedra. Four octahedra form a Ge4O16, and these clusters are connected to one another via the tetrahedra. The superstructure shows a slight distortion of the average framework.