Hydrothermal Synthesis of (C₆N₂H₁₄)₂(U^VI₂U^IVO₄F₁₂), a Mixed-Valent One-Dimensional Uranium Oxyfluoride

Abstract

A new hybrid organic-inorganic mixed-valent uranium oxyfluoride, (C6N2H14)2(U3O4F12), UFO-17, has been synthesized under hydrothermal conditions using uranium dioxide as the uranium source, hydrofluoric acid as mineralizer, and 1,4-diazabicyclo[2.2.2]octane as template. The single-crystal X-ray structure was determined. Crystals of UFO-17 belonged to the orthorhombic space group Cmcm (no. 63), with a = 14.2660(15) A, b = 24.5130(10) A, c = 7.201(2) A, and Z = 4. The structure reveals parallel uranium-containing chains of two types: one type is composed of edge-sharing UO2F5 units; the other has a backbone of edge-sharing UF8 units, each sharing an edge with a pendant UO2F5 unit. Bond-valence calculations suggest the UF8 groups contain UIV, while the UO2F5 groups contain UVI. EXAFS data give results consistent with the single-crystal X-ray structure determination, while comparison of the uranium LIII-edge XANES of UFO-17 with that of related UIV and UVI compounds supports the oxidation-state assignment. Variable-temperature magnetic susceptibility measurements on UFO-17 and a range of related hybrid organic-inorganic uranium(IV) and uranium(VI) fluorides and oxyfluorides further support the formulation of UFO-17 as a mixed-valent UIV/UVI compound.

Hydrothermal Syntheses, Structures, and Magnetic Properties of the U(IV) Fluorides (C5H14N2)2U2F12·5H2O and (NH4)7U6F31

“…5a and 5b). The e!ective moments of (300 K)"3.05 and 3.03 /U(IV) for AU1-2 and (NH ) U F , respectively, fall within the range observed for other organic/inorganic uranium(IV) #uorides (1,6,7,10). The e!ective moment continues to rise at high temperatures, which is re#ected in the large values of !97 and !126 K for AU1-2 and (NH ) U F , respectively.…”

“…AU1-2 and (NH ) U F possess very similar U(IV) coordination environments and U}U distances. However, (C H N ) U F ) H O (UFO-6; (300 K)"3.59 /U(IV)) contains a one-dimensional chain with U(IV) coordination and U}U distances similar to those of AU1-2 and yet shows substantially di!erent magnetic susceptibility behavior (10). The determination of crystalline electric "eld, spin-orbit, and exchange e!ects on the temperature dependence of the magnetic susceptibility are then required for a further understanding of the magnetism of these low-dimensional U(IV) #uorides.…”

Synthesis and characterization of mixed An(IV)An(III) oxalates (An(IV)=Th, Np, U or Pu and An(III)=Pu or Am)

“…A range of mixed-valent uranium compounds [24][25][26][27][28][29] has previously been reported with different inorganic and/or organic ligands and different pairs of oxidation states (IV-V; IV-VI or V-VI). In most of these mixed-valence compounds, the environment of uranium atoms depends on the oxidation state.…”

Hydrothermal Synthesis, Structure and Thermal Stability of Diamine Templated Layered Uranyl‐Vanadates.

“…One approach for designing novel layered and microporous uranium-bearing materials is to exert influence over structural features through the introduction of templating agents. Amines have historically been used as charge balancing, space filling and templating agents in various systems including molybdate [9][10][11][12][13], phosphate [14][15][16][17][18], phosphite [19], selenate [20], selenite [21], arsenate [17] sulfate [22][23][24][25][26][27][28][29][30][31] and fluoride containing compounds [18,[31][32][33][34][35][36][37][38][39] but organically templated uranyl-vanadates systems remained unexplored so far.…”