Synthesis, structure, and upconversion studies on organically templated uranium phosphites

Abstract

Three new amine templated uranium phosphites, [C₂N₂H₁₀] [U₂^IVF₆(HPO₃)₂], 1, [C₄N₂H₁₂][U₂^IVF₆ (HPO₃)₂], 2, and [C₄N₂H₁₂] [(U^VIO₂)₂F₂(HPO₃)₂], 3, have been synthesized by hydrothermal methods. All of the compounds are built up from a connectivity between U(O/F)_x (x = 7, 8) and HPO₃ polyhedral units. The observation of a well-established secondary building unit, SBU-4, in 1 and 2 is noteworthy. In 1, the SBU-4 units are connected to form U-F-U chains, which are linked by U-O-P chains, forming the layered structure. In 2, the SBU-4 units are edge-shared and also interconnected forming the 3D structure. In 3, the connectivity between the building units forms a layer, the topology of which is similar to the mineral, johannite. To the best of our knowledge, this is the first observation of a well-known secondary building unit (SBU-4) in actinide framework compounds. Optical studies on 1 and 2, containing U⁴⁺ species, indicate an intense blue emission through an upconversion process, and the magnetic susceptibility studies show antiferromagnetic behavior.