Synthesis and characterization of uranyl complexes containing orotate and isoorotate

The synthesis and structural characterization of three new Uranyl Organic Frameworks (UOFs) – ([UO₂(C₅H₃N₂O₄)₂(H₂O)₃]·2H₂O (1), (H₃O)₃[(UO₂)₄(C₅HN₂O₄)(O)₄] (2), and H₃O[UO₂(C₅H₂N₂O₄)(OH)] (3) – in which uranyl ($U{O}_2^{2+})$ is coordinated to either orotate (1 and 2) or isoorotate (3) with varying coordination modes and denticities, is presented. Complex 1 was prepared via slow evaporation from a mixed solvent (ethanol–water), while complexes 2 and 3 were prepared via a hydrothermal methodology. Single crystal X-ray diffraction analysis reveals that 1 is a 0D structure, 2 is a 2D structure, and 3 is a 1D structure. In each complex, uranium exhibits an approximately pentagonal bipyramidal geometry, a result of the linear dioxo uranyl unit being coordinated by water, orotate/isoorotate, and/or other uranyl units in the equatorial region. The observed coordination mode(s) of orotate (in 1) and isoorotate (in 3) are consistent with what has previously been reported. However, in complex 2, the orotate ligand is bound through every possible donor atom (two carboxylate oxygens, two carbonyl oxygens, and two nitrogen atoms). This is the first example of orotate coordinated in this manner. Herein, the synthesis, characterization, and structural descriptions of these new complexes is presented.