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 UO 2 (H 2 O)(1,2-bdc)·0.32H 2 O (1,2-bdc = phthalate) crystallizes at low pH (0.9−1.5). Its structure is built up from pentagonal bipyramids (UO 2 )O 4 (H 2 O) linked to each other through the phthalate groups and defines infinite nanotubular 1D motifs delimited by six uranyl centers. The two other compounds A(UO 2 ) 3 O(OH)(H 2 O)(1,2-bdc) 2 (A = K, NH 4 ) are formed for higher pH (1.5−3). They are isostructural and consist of the 1D connection of dinuclear units (UO 2 ) 2 O 4 (μ 2 -OH) 2 (H 2 O) 2 with tetranuclear units (UO 2 ) 4 (μ 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.