REI₅O₁₄ (RE=Y and Gd): Promising SHG Materials Featuring the Semicircle‐Shaped I₅O₁₄³⁻ Polyiodate Anion

Abstract

The first examples of rare-earth polyiodates, namely, REI₅ O₁₄ (RE=Y and Gd), have been prepared by hydrothermal reactions of RE₂ O₃ and H₅ IO₆ in H₃ PO₄ (≥85 wt % in H₂ O), with extremely high yields (>95 %). They crystalize in the polar space group Cm and feature a brand-new semicircle-shaped [I₅ O₁₄ ]^3- pentameric polyiodate anion composed of two IO₃ and three IO₄ polyhedra. Remarkably, both compounds exhibit very large second-harmonic generation (SHG) signals (14× and 15×KH₂ PO₄ (KDP) upon 1064 nm laser radiation for Y and Gd compounds, respectively). Our work shows that the hydrothermal reaction in a phosphoric acid medium facilitates the formation of rare-earth polyiodates.