Occurence of an Octanuclear Motif of Uranyl Isophthalate with Cation–Cation Interactions through Edge-Sharing Connection Mode

An uranyl isophthalate has been hydrothermally synthesized at 200 °C for 24 h, from a mixture of uranyl nitrate, isophthalic acid, and hydrazine in water. It was characterized by single-crystal analysis [triclinic, P1̅, a = 7.3934(3) Å, b = 13.3296(5) Å, c = 15.4432(5) Å, α = 111.865(2)°, β = 90.637(2)°, γ = 104.867(2)°, V = 1355.49(9) Å3] and different spectroscopic techniques (Raman, IR-ATR, UV–visible). The 3D structure of the phase (UO2)8O2(OH)4(H2O)4(1,3-bdc)4·4H2O (1,3-bdc = 1,3-benzenedicarboxylate) reveals octanuclear units based on the association of 7-fold coordinated uranyl cations (pentagonal bipyramid) involving a rare case of cation–cation interaction together with edge-sharing polyhedral connection mode. UV–visible absorption spectroscopy confirmed that uranium was only involved in the structure as uranyl forms (excluding the presence of tetravalent or pentavalent uranium). Additionally, μ-Raman and IR-ATR experiments allowed assigning four uranyl contributions to the four types of uranyl entities in the structure, in agreement with the XRD analysis.