Cs4UGe8O20: a tetravalent uranium germanate containing four- and five-coordinate germanium.

A very rare tetravalent uranium germanate has been synthesized under hydrothermal conditions at 585 °C and 160 MPa. Its structure contains layers of single-ring Ge3O96– germanate anions that are connected by UO6 octahedra and dimers of edge-sharing GeO5 trigonal bipyramids to form a three-dimensional framework with intersecting 6- and 7-ring channels. UV–visible, photoluminescence, and U 4f X-ray photoelectron spectroscopy were used to confirm the valence state of uranium.