Revisiting the Uranyl-phthalate System: Isolation and Crystal Structures of Two Types of Uranyl−Organic Frameworks (UOF)

Three uranyl phthalates have been hydrothermally synthesized (200 °C, 24 h) and characterized by means of single-crystal X-ray diffraction analysis. The compound UO2(H2O)(1,2-bdc)·0.32H2O (1,2-bdc = phthalate) crystallizes at low pH (0.9−1.5). Its structure is built up from pentagonal bipyramids (UO2)O4(H2O) linked to each other through the phthalate groups and defines infinite nanotubular 1D motifs delimited by six uranyl centers. The two other compounds A(UO2)3O(OH)(H2O)(1,2-bdc)2 (A = K, NH4) are formed for higher pH (1.5−3). They are isostructural and consist of the 1D connection of dinuclear units (UO2)2O4(μ2-OH)2(H2O)2 with tetranuclear units (UO2)4(μ3-O)2O12 via the phthalate groups. The cationic A species are intercalated between the mixed organic−inorganic chains. Discussion of the formation of these different phases was given as a function of pH.