Web Release Date: January 1,
The First Organically Templated Tetravalent Uranium Phosphates with Dimer-Structured Topologies
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan, Department of Electronic Materials, Far East University, Tainan 74448, Taiwan, and Department of Chemistry, National Central University, Chungli 32054, Taiwan
Received September 28, 2007
Revised Manuscript Received November 28, 2007
Abstract:
Four new organically templated uranium(IV) phosphates, (C4H16N3)[U2F3(PO4)2(HPO4)] (1), (C6H21N4)[U2F4(PO4)(HPO4)2] (2), (C4H16N3)2[U2F10(HPO4)2] (3), and (C6H16N2)2(UF7)(H2PO4) (4), have been successfully synthesized in pure-phase form under mild solvothermal conditions and characterized by single-crystal X-ray diffraction, magnetic susceptibility, thermogravimetric analysis (TGA), elemental analysis, inductively coupled plasma−atomic emission spectroscopy, and fluorine analysis. They are the first tetravalent uranium phosphates with encapsulated organic templates ever reported. All four materials display unique dimer-structured topologies with various dimensionalities in the inorganic/hydrogen-bonded networks. In this series, U4+ ions are located in the center of bicapped trigonal prisms of UFO7, UF2O6, UF6O2, or UF8, from which edge-sharing U2FmO14−m dimers (m = 2 and 4 in 1, m = 4 in 2, m = 10 in 3, and m =14 in 4) are formed. The less-fluorinated U2F2O12 and U2F4O10 dimers are connected to eight and six phosphate groups to give two-dimensional layer and one-dimensional chain structures, respectively; the more-fluorinated U2F10O4 and fully fluorinated U2F14 dimers are respectively attached by two or zero phosphate groups to form clustered structures. TGA results indicated that the layered structure of 1 could sustain heating up to ~300 °C and the thermal stability of the series steadily decreased with decreasing structural dimensionality. The 4+ oxidation state of uranium was confirmed by bond-valence-sum calculations and magnetic susceptibility measurements. In view of radioactive mobility, we discovered that 1 and 2 could be more stable than UO2 under sufficiently oxidizing conditions. Crystal data: triclinic, space group P1̅, a = 9.1657(4) Å, b = 10.0618(4) Å, c = 10.7584(4) Å, α = 73.668(1)°, β = 65.366(1)°, γ = 65.916(1)°, and Z = 2 for 1; monoclinic, P21/c, a = 11.1124(4) Å, b = 19.6830(8) Å, c = 10.1466(4) Å, β = 114.362(1)°, and Z = 4 for 2; monoclinic, space group P21/n, a = 18.383(1) Å, b = 7.8448(6) Å, c = 18.442(1) Å, β = 113.967(1)°, and Z = 4 for 3; monoclinic, P21/c, a = 10.2346(9) Å, b = 23.846(2) Å, c = 8.8091(8) Å, β = 93.459(2)°, and Z = 4 for 4.
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