U3F12(H2O), a noncentrosymmetric uranium(IV) fluoride prepared via a convenient in situ route that creates U4+ under mild hydrothermal conditions.

A new noncentrosymmetric U(4+)-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 U(4+)(f(2))-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.