Two new uranyl fluoride complexes with U^VIO-alkali (Na, Cs) interactions: Experimental and theoretical studies

Two new layered 3D uranyl fluoride complexes: Na₃(UO ₂)₂F₃(OH)₄(H₂O) ₂ (1) and Cs(UO₂)₂F₅ (2) have been prepared using the hydrothermal method and characterized via single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group C2/c [a = 15.125(3) Å, b = 6.941(1) Å, c = 11.257(2) Å, and β = 94.76(3)°] and compound 2 in the orthorhombic space group Cmcm [a = 12.149(2) Å, b = 11.862(2) Å, c = 12.366(2) Å], respectively. Both of them possess extended 3D structures. Furthermore, U^VIO- alkalis (Na, Cs) interactions were observed in two compounds, which is relatively rare in U(vi) complexes. By introducing alkali ions, the layered structures can be further assembled into three-dimensional ones. Density functional theory (DFT) studies confirmed that the interactions between the alkalis and the oxygens of uranyl mainly ionic with small proportion of covalency, which results in the formation of these uranyl fluoride complexes with 3D structures.