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

The U(IV) fluorides (C5H14N2)2U2F12·5H2O and (NH4)7U6F31 have been prepared from the reaction of UO3 with HF and homopiperazine (C5H12N2) at 180 C in aqueous media. AU1-2 contains dodecahedral UF8 units that share two edges to form 1∞[UF4F4/2] one-dimensional chains. The fluoride ligands form hydrogen bonds with the diprotonated homopiperazinium cations to yield channels running down the a axis that contain occluded water molecules. (NH4)7U6F31 is isostructural with Na7Zr6F31, forming a three-dimensional network consisting of edge- and corner-sharing UF8 square antiprisms that create cubooctahedral clusters and small intersecting channels. A disordered fluoride anion resides in the cubooctahedral cavities and the ammonium cations partially fill the channels. AU1-2 and (NH4)7U6F31 display similar magnetic behavior with μeff (300 K)=3.05 and 3.03 μB/U(IV) and θ=-97 and -126 K, respectively. Crystallographic data: AU1-2, monoclinic, space group P21/n, a=6.545(3) angstrom, b=19.90(1) angstrom, c=19.07(1) angstrom, β=98.89(4)o, Z=4, λ=0.71073 angstrom, R(F)=0.0395 for 293 parameters with 3282 reflections with I>2σ(I); (NH4)7U6F31, rhombohedral, space group Rbar 3, a=15.371(3) angstrom, c=10.791(3) angstrom, Z=3, λ=0.71073 angstrom, R(F)=0.0242 for 82 parameters with 841 reflections with I>2σ(I)