K3(U3O6)(Si2O7) and Rb3(U3O6)(Ge2O7):: A pentavalent-uranium silicate and germanate

A new uranium(V) silicate, K-3(U3O6)(Si2O7), and the germanate analogue, Rb-3(U3O6)(Ge2O7), have been synthesized under high-temperature, high-pressure hydrothermal conditions and characterized by single-crystal X-ray diffraction. Their structures contain uranate columns formed of triple octahedral chains of the alpha-UF5 type linked by disilicate (or digermanate) units to form a 3-D framework structure. The valence state of uranium is confirmed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and magnetic susceptibility.