Mixed-Valence Uranium Germanate and Silicate: Cs_x(U^VO)(U^IV/VO)₂(Ge₂O₇)₂ (x = 3.18) and Cs₄(U^VO)(U^IV/VO)₂(Si₂O₇)₂

Abstract

A new mixed-valence uranium germanate and the silicate analogue have been synthesized under hydrothermal conditions at 600 °C and 165 MPa. Their crystal structures contain infinite -U(V)-O-U(IV/V)-O-U(IV/V)-O-U(V)- chains that are connected by Ge(2)O(7) or Si(2)O(7) groups to form a 3D framework with six-ring channels where the Cs(+) cations are located. Two of the Cs sites in the germanate are partially occupied. Bond-valence-sum calculation and an U 4f X-ray photoelectron spectroscopy study confirm the valence states of the uranium.