Hydrothermal syntheses, structures, and magnetic properties of the U(IV) fluorides (C5H14N2)2U2F12•5H2O and (NH4)7U6F31

The U(IV) fluorides (C5H14N2)(2)U2F12. 5H(2)O (AU1-2) and (NH4)(7)U6F31 have been prepared from the reaction of UO3 with HF and homopiperazine (C5H12N2) at 180 degreesC in aqueous media. AU1-2 contains dodecahedral UF, units that share two edges to form (1)(infinity)[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. (N-H)(7)U6F31 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)(7)U6F31 display similar magnetic behavior with mu (eff) (300 K) = 3.05 and 3.03 mu (B)/U(TV) and theta = - 97 and - 126 K, respectively. Crystallographic data: AU1-2, monoclinic, space group P2(1)/n, a = 6.545(3) Angstrom, b = 19.90(1) Angstrom, c = 19.07(1) Angstrom, beta = 98.89(4)degrees, Z = 4, lambda = 0.71073 Angstrom, R(F)=0.0395 for 293 parameters with 3282 reflections with I > 2 sigma (I); (NH4)(7)U6F31, rhombohedral, space group R (3) over bar, 15.371(3) Angstrom, c = 10.791(3) Angstrom, Z = 3, lambda = 0.71073 Angstrom, R(F)= 0.0242 for 82 parameters with 841 reflections with I > 2 sigma (I) (C) 2001 Academic Press.