The structure of a novel mixed-valent chromium uranyl compound, (C3NH10)(10)[(UO2)(13)(Cr125+O42)(Cr6+O4)(6)(H2O)(6)](H2O)(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 x 18.5 angstrom(2) and a height of about 8 angstrom. The hemispheres are centered by a UO8 hexagonal bipyramid surrounded by six dimers of Cr5+O5 square pyramids, UO7 pentagonal bipyramids, and Cr6+O4 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 U21Cr23 and can be considered as derivatives of nanospherical cluster U26Cr36 composed of three-, four-, and five-membered rings.