Uranyl Halides from Liquid Ammonia: [UO2(NH3)5]Cl2·NH3 and [UO2F2(NH3)3]2·2NH3 and Their Decomposition Products [UO2Cl2(NH3)3] and [UO2F2(NH3)3

Abstract

AbstractUranyl chloride UO2Cl2 and uranyl fluoride UO2F2 react with dry liquid ammonia under the formation of traffic‐green crystals of pentaammine dioxido uranium(VI) dichloride ammonia (1/1) [UO2(NH3)5]Cl2·NH3 (1) and sulfur‐yellow crystals of triammine difluorido dioxido uranium(VI) ammonia (2/2) [UO2F2(NH3)3]2·2NH3 (2), respectively. Low‐temperature X‐ray structure analyses on single crystals of the two compounds were conducted. Compound 1 crystallizes in the orthorhombic space group Cmcm with a = 12.7865(2), b = 10.5106(2), c = 8.7089(2) Å, V = 1170.45(4) Å3 at 123 K with Z = 4. Compound 2 crystallizes in the orthorhombic space group Pnma with a = 20.8451(5), b = 9.1267(2), c = 8.3371(2) Å, V = 1586(6) Å3 at 123 K with Z = 4. Further investigations on the room‐temperature decomposition products of compounds 1 and 2 by Raman and IR spectroscopy, TGA MS and X‐ray powder diffraction measurements and deuteration studies led to the identification of triammine dichlorido dioxido uranium(VI) UO2Cl2(NH3)3 (3) and triammine difluorido dioxido uranium(VI) UO2F2(NH3)3 (4) in the form of fern‐green and zinc‐yellow powders. Quantum chemical studies at the DFT‐PBE0/TZVP level of theory support the experimental observations andalso show that the O≡U≡O triple bonding in the [UO2F2(NH3)3] molecule of compound 2 is weaker in comparison to the one in the [UO2(NH3)5]2+ dication of compound 1.