Hydrothermal synthesis and characterization of [(UO₂) ₂F₈(H₂O)₂Zn₂(4,4′- bpy)₂]·(4,4′-bpy), a mixed-metal uranyl aquofluoride with a pillared layer structure

A mixed-metal uranyl aquofluoride, [(UO₂)₂F ₈(H₂O)₂Zn₂(4,4′-bpy) ₂]·(4,4′-bpy), has been synthesized under hydrothermal conditions and has been structurally characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, emission spectroscopy, and solid-state NMR spectroscopy. It is one of the few uranium fluoride-organic framework solids in which an organic molecule is directly incorporated into the extended structure of the metal fluoride and is the first example of mixed-metal uranium oxyfluoride incorporating an organic ligand. The structure consists of neutral layers of edge- and corner-sharing uranium-centered pentagonal bipyramids and zinc-centered octahedra, which are linked through 4,4′-bpy ligands into a 3-D framework. The ¹H MAS NMR spectrum is in support of the conclusion that the occluded 4,4′-bpy molecules in the structural channels are not protonated. Crystal data: monoclinic, space group P2₁/c, a = 9.4630(5) Å, b = 22.384(1) Å, c = 16.7534(8) Å, β = 91.899(2)°, V = 3546.7(4) ų and Z = 4.