Mixed-Valence Uranium Germanate and Silicate: Csx(UVO)(UIV/VO)2(Ge2O7)2 (x = 3.18) and Cs4(UVO)(UIV/VO)2(Si2O7)2

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 −UV–O–UIV/V–O–UIV/V–O–UV– chains that are connected by Ge2O7 or Si2O7 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.