Revisiting the uranyl-phthalate system: Isolation and crystal structures of two types of uranyl-organic frameworks (UOF)

摘要

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_2O)(1,2-bdc)·0.32H_2O (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_2O) 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)_3O(OH)(H_2O)(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) _2O_4(μ_2-OH)_2(H_2O) _2 with tetranuclear units (UO_2) _4(μ_3-O)_2O_(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.