An X-ray crystallographic, Raman, and infrared spectral study of crystalline potassium uranyl carbonate, K₄UO₂(CO₃)₃

Abstract

X-ray diffraction studies have revealed that K 4 UO 2 (CO 3 ) 3 is isostructural with (NH 4 ) 4 UO 2 (CO 3 ) 3 ; the crystal is monoclinic with a = 10.247(3), b = 9.202(2), c = 12.226(3) Å, β = 95.11(2)°, Z = 4, and space group C2/c. Three carbonate anions are arranged in bidentate fashion in the equatorial plane of UO 2 2+ ; one of these occupies a C 2 site and the other two occupy C 1 sites. All carbonates are significantly distorted from D 3h symmetry. The binding of carbonates to uranyl is strong and thus the lattice can be considered to be composed of [UO 2 (CO 3 ) 3 ] 4− anions and K + cations. The Raman and infrared spectra exhibit fewer lines than predicted for such a crystal. Tentative assignments are suggested for the more prominent bands of the constituent polyatomic species.