The structure of a novel mixed-valent chromium uranyl compound, (C ₃NH ₁₀) ₁₀[(UO ₂) ₁₃(Cr ₁₂ ⁵⁺O ₄₂)(Cr ⁶⁺O ₄) ₆(H ₂O) ₆](H ₂O) ₆ (1), obtained by the combination of a hydrothermal method and evaporation from aqueous solutions with isopropylammonium, contains uranyl chromate hemispheres with lateral dimensions of 18.9 × 18.5 Å ² and a height of about 8 Å. The hemispheres are centered by a UO ₈ hexagonal bipyramid surrounded by six dimers of Cr ⁵⁺O ₅ square pyramids, UO ₇ pentagonal bipyramids, and Cr ⁶⁺O ₄ tetrahedra. The hemispheres are linked into two-dimensional layers so that two adjacent hemispheres are oriented in opposite directions relative to the plane of the layer. From a topological point of view, the hemispheres have the formula U ₂₁Cr ₂₃ and can be considered as derivatives of nanospherical cluster U ₂₆Cr ₃₆ composed of three-, four-, and five-membered rings.