Crystal Growth and Structure Analysis of Ce ₁₈ W ₁₀ O ₅₇ : A Complex Oxide Containing Tungsten in an Unusual Trigonal Prismatic Coordination Environment

The noncentrosymmetric tungstate oxide, Ce 18 W 10 O 57, was synthesized for the first time as high-quality single crystals via the molten chloride flux method and structurally characterized by single-crystal X-ray diffraction. The compound is a structural analogue to the previously reported La 18 W 10 O 57, which crystallizes in the hexagonal space group P 6̅2 c . The +3 oxidation state of cerium in Ce 18 W 10 O 57 was achieved via the in situ reduction of Ce(IV) to Ce(III) using Zn metal. The structure consists of both isolated and face-shared WO 6 octahedra and, surprisingly, isolated WO 6 trigonal prisms. A careful analysis of the packing arrangement in the structure makes it possible to explain the unusual structural architecture of Ce 18 W 10 O 57, which is described in detail. The temperature-dependent magnetic susceptibility of Ce 18 W 10 O 57 indicates that the cerium(III) f 1 cations do not order magnetically and exhibit simple paramagnetic behavior. The SHG efficiency of Ln 18 W 10 O 57 (Ln = La, Ce) was measured as a function of particle size, and both compounds were found to be SHG active with efficiency approximately equal to that of α-SiO 2 .