Synthesis, Structure, and Upconversion Studies on Organically Templated Uranium Phosphites

Three new amine templated uranium phosphites, [C2N2H10][U2IVF6(HPO3)2], 1, [C4N2H12][U2IVF6(HPO3)2], 2, and
[C4N2H12][(UVIO2)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.