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 K₄UO₂(CO₃)₃ is isostructural with (NH₄)₄UO₂(CO₃)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 UO₂²⁺; one of these occupies a C₂ site and the other two occupy C₁ 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 [UO₂(CO₃)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.