A new series of pillared uranyl-vanadates based on uranophane-type sheets in the uranium-vanadium-linear alkyl diamine systems

A new family of three-dimensional (3D) uranyl vanadates (C3N2H12){[(UO2)(H2O)][(UO2)(VO4)]4}·1H2O (C3UV), (C4N2H14){[(UO2)(H2O)][(UO2)(VO4)]4}·2H2O (C4UV), (C5N2H16) {[(UO2)(H2O)][(UO2)(VO4)]4} (C5UV), (C6N2H20) {[(UO2)(H2O)][(UO2)(VO4)]4} (C6UV) and (C7N2H22) {[(UO2)(H2O)][(UO2)(VO4)]4} (C7UV) was prepared from mild-hydrothermal reactions using 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane and 1,7-diaminoheptane as structure directing agents. The five compounds are orthorhombic, space group Cmc21, with a≈15.6, b≈14.1, c≈13.6 Å. The structures were solved using single-crystal X-ray diffraction data. The compounds contain the same three-dimensional inorganic framework built from uranyl-vanadate layers of uranophane-type anion topology pillared by [UO6(H2O)] pentagonal bipyramids. The doubly protonated diamines reside in the cavities created by the inorganic framework and are linked to the inorganic framework through hydrogen bonds involving one nitrogen atom. The structure is compared with that of uranyl-phosphates and uranyl-arsenates containing alkaline metals. The use of alkaline metals for the synthesis of uranyl-vanadates leads to carnotite-type compounds.