Synthesis and structure of the new pentanary uranium(vi) silicate, K4CaUSi4O14, a member of a structural family related to fresnoite

Abstract

Single crystals of K₄CaUSi₄O₁₄ have been grown from a eutectic CaF₂–KF flux. K₄CaUSi₄O₁₄ crystallizes in a new structure which exhibits a 49-fold superstructure believed to be due to a modulation of the uranium and silicon polyhedra. We report the sub-cell of the structure which adopts the tetragonal space group Pn2 with lattice parameters a = 9.2862(2) Å, c = 8.3796(4) Å, and V = 722.60(5) ų. K₄CaUSi₄O₁₄ is a member of a structural family related to the mineral fresnoite which we describe here. Finally, we report UV-vis absorbance and SHG measurements on the compound, which is non-centrosymmetric.