Insight into the Uranyl Oxyfluoride Topologies through the Synthesis, Crystal Structure, and Evidence of a New Oxyfluoride Layer in [(UO2)4F13][Sr3(H2O)8](NO3)·H2O

A new strontium uranyl oxyfluoride, [(UO2)4F13]­[Sr3(H2O)8]­(NO3)·H2O, was synthesized under hydrothermal conditions. The single-crystal X-ray structure was determined. This compound crystallizes in the triclinic space group P1̅ (No. 2), with unit cell parameters a = 10.7925(16) Å, b = 10.9183(16) Å, c = 13.231(2) Å, α = 92.570(8)°, β = 109.147(8)°, γ = 92.778(8)°, V = 1468.1(4) Å3, and Z = 2. The structure is built from uranyl-containing [(UO2)4F13]∞1 chains of tetrameric units of corner-sharing UO2F5 pentagonal bipyramids. These chains are linked through trimeric strontium units to form strontium–uranyl oxyfluoride layers further assembled by nitrate groups. The interlayer space is occupied by free water molecules. This compound was characterized by spectroscopic methods, especially 19F NMR highlighting the many different fluoride sites. Structural relationships with other uranyl oxyfluorides were investigated through the different F/O ratios, the structural building unit, and the structural arrangement.