Crystal structure of K[UO2(NO3)3] and some features of compounds M[UO2(NO3)3] (M = K, Rb, and Cs)

Greenish-yellow transparent crystals of K[UO2(NO 3)3] were prepared from aqueous solutions as by-product in synthesis of potassium chromatouranylates. The crystal structure was solved by the direct methods and refined to R1 = 0.037 (wR2 = 0.070) for 1452 reflections with |Fhkl|≥4σ|Fhkl|. Monoclinic system, space group C2/c, a = 13.4877(10), b = 9.5843(7), b = 7.9564(6) Å, β = 116.124(2)°, V = 923.45(12) Å3. The structure of K[UO2(NO3)3] contains isolated complex ions [UO2(NO3)3]- whose uranyl groups are aligned parallel to the [1̄01] plane. The K + cations, coordinated by twelve oxygen atoms, are located between the complex anions. Comparison of the structure with known data on M[UO 2(NO3)3] compounds (M = K, Rb, Cs) suggests the possibility of phase transitions due to relatively small displacements of [UO2(NO3)3]- anions and K + cations, retaining the general structural motif.