U3F12(H2O), a Noncentrosymmetric Uranium(IV) Fluoride Prepared via a Convenient In Situ Route That Creates U4+ under Mild Hydrothermal Conditions

A new noncentrosymmetric U4+-containing fluoride, U3F12(H2O), has been synthesized via a mild hydrothermal route and its crystal structure determined by single-crystal X-ray diffraction. The material exhibits a complex three-dimensional structure that is based on [U6F33(H2O)2)]9– hexanuclear building units consisting of corner- and edge-shared UF8, UF9, and UOF7 polyhedra. Powder second-harmonic generation (SHG) measurements revealed that the SHG efficiency for U3F12(H2O) is comparable to that of α-SiO2. Magnetic susceptibility measurements indicated that the U4+(f2)-containing material exhibits a singlet ground state at low temperature. IR and UV–vis reflectance spectra were obtained, and the thermal behavior was investigated by thermogravimetric analysis.