Oleum and Sulfuric Acid as Reaction Media: The Actinide Examples UO2(S2O7)‐lt (low temperature), UO2(S2O7)‐ht (high temperature), UO2(HSO4)2, An(SO4)2 (An = Th, U), Th4(HSO4)2(SO4)7 and Th(HSO4)2(SO4)

New uranium sulfates have been synthesised by the reaction of UO2(CH3COO)2·2H2O with sulfuric acid/sulfur trioxide mixtures in sealed glass ampoules. Both polymorphs of the disulfate UO2(S2O7) [low temperature (lt): triclinic, P1̄ , Z = 2, a = 647.8(1) pm, b = 684.2(1) pm, c = 800.1(1) pm, α = 87.31(2)°, β = 78.37(2)°, γ = 75.34(2)°, V = 0.33605(9) nm3; high temperature (ht): orthorhombic, Pca21, Z = 8, a = 1080.21(2) pm, b = 814.74(1) pm, c = 1655.63(3) pm, V = 1.45710(4) nm3] and the hydrogensulfate UO2(HSO4)2 [monoclinic, P21/n, Z = 4, a = 779(3) pm, b = 815.39(3) pm, c = 1285.77(5) pm, β = 103.700(1)°, V = 0.79428(5) nm3] contain hexavalent uranium in the form of the well‐known linear [UO2]2+ ion. The pentagonal bipyramidal coordination sphere around U is completed by disulfate and hydrogensulfate ions, which connect the uranyl groups to a three‐dimensional network. Reaction of uranyl acetate with sulfuric acid at sufficiently high temperature (300 °C) leads to a reduction of uranium to the tetravalent form under separation of green plates of U(SO4)2 [orthorhombic, Pbca, Z = 8, a = 940.11(2) pm, b = 898.13(2) pm, c = 1349.09(3) pm, V = 1.13909(4) nm3]. The U4+ ions in U(SO4)2 are in a square antiprismatic coordination of eight monodentate sulfate tetrahedra. By treatment of ThO2 with sulfuric acid, the thorium (hydrogen)sulfates Th(SO4)2 [orthorhombic, Pbca, Z = 8, a = 953.74(3) pm, b = 911.49(3) pm, c = 1365.02(4) pm, V = 1.18665(6) nm3], Th4(HSO4)2(SO4)7 [tetragonal, I4̄ 2d, Z = 4, a = 1327.7(2) pm, c = 1362.8(2) pm, V = 2.402.3(6) nm3] and Th(HSO4)2(SO4) [triclinic, P1̄ , Z = 2, a = 576.18(2) pm, b = 896.11(3) pm, c = 948.58(3) pm, α = 65.387(2)°, β = 87.838(2)°, γ = 88.917(2)°, V = 0.44495(3) nm3] could be obtained. Whereas Th(SO4)2 is isotypic with the respective uranium compound, both hydrogensulfates contain ninefold‐coordinated thorium to form a triple‐capped trigonal prism. The structure of Th(HSO4)2(SO4) can be described as a distorted variant of the UCl3 structure type.