Crystal Structure of (H3O)2[(UO2)2(SO4)3(H2O)] · 6.86H2O, a New Hydroxonium Diuranyltrisulfate Aqua Complex

Abstract

Single crystals of earlier unknown hydroxonium monoaquatrisulfatodiuranylate 6.86-hydrate (H₃O)₂[(UO₂)₂(SO₄)₃(H₂O)] · 6.86H₂O (I) have been synthesized via the evaporation of an aqueous [UO₂(NO₃)₂(H₂O)₂] · nH₂O (n = 2, 4) solution containing sulfuric and nitric acids in air at room temperature. The structure of complex I has been studied by X-ray diffraction. Crystals are monoclinic, а = 15.0903(12) Å, b = 9.9191(8) Å, c = 15.6099(13) Å, β = 112.560(1)°, space group P2₁/n, Z = 4, V = 2157.7(3) ų. The complex is formed due to electrostatic attraction forces between counterions and stabilized by hydrogen bonds. Its main structural element is the [(UO₂)₂(SO₄)₃H₂O] _n^2- framework. The structure contains two types of uranium atoms surrounded by oxygen atoms according to a pentagonal bipyramid motif. The coordination polyhedra of all the three crystallographically different S atoms are SO₄^2- tetrahedra. The U(1) atom in the equatorial bipyramid plane is monodentately bonded to the oxygen atoms of five SO₄^2- tetrahedra, while the U(2) atom is monodentately coordinated to four sulfate groups and one water molecule.