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 degrees C, 24 h) and characterized by means of single crystal X-ray diffraction analysis. The compound UO2(H2O)(1,2-bdc)center dot 0.32H(2)O (1,2-bdc = phthalate) crystallizes at low pH (0.9-1.5). Its structure is built up from pentagonal bipyramids (UO2)O-4(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)(3)O(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)(2)O-4(mu(2)-OH)(2)(H2O)(2) with tetranuclear units (UO2)(4)(mu(3)-O)(2)O-12 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.