REI O (RE=Y and Gd): Promising SHG Materials Featuring the Semicircle-Shaped I O Polyiodate Anion.

The first examples of rare-earth polyiodates, namely, REI O (RE=Y and Gd), have been prepared by hydrothermal reactions of RE O and H IO in H PO (≥85 wt % in H O), with extremely high yields (>95 %). They crystalize in the polar space group Cm and feature a brand-new semicircle-shaped [I O ] pentameric polyiodate anion composed of two IO and three IO polyhedra. Remarkably, both compounds exhibit very large second-harmonic generation (SHG) signals (14× and 15×KH PO (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.