Explorations of New Second-Order Nonlinear Optical Materials in the K<sup>I</sup>-M<sup>II</sup> -I<sup>V</sup>-O Systems

Explorations of new second-order nonlinear optical (NLO) materials in the K<sup>I</sup>-M<sup>II</sup> -I<sup>V</sup>-O systems led to four novel mixed metal iodates, namely, K<sub>2</sub>M(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> (M = Mn, Co, Zn, Mg). The four compounds are isostructural and crystallize in space group <i>I</i>2 which is in the chiral and polar crystal class 2. Their structure features zero-dimensional {M(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>}<sup>2−</sup> anions that are separated by K<sup>+</sup> cations. The M(II) centers are ligated by two aqua ligands in trans fashion and four monodentate iodate anions. The K<sup>+</sup> cation is eight-coordinated by two iodate anions in bidentate chelating fashion and four other iodates in a unidentate fashion. Second harmonic generation (SHG) measurements indicate that K<sub>2</sub>Zn(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> and K<sub>2</sub>Mg(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> display moderate SHG responses that are approximately 2.3 and 1.4 times of KH<sub>2</sub>PO<sub>4</sub> (KDP), respectively, and they are also phase-matchable. The SHG response of K<sub>2</sub>Co(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> is much weaker (about 0.3×KDP), and no obvious SHG signal was detected for K<sub>2</sub>Mn(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>. Results of optical property calculations for the Zn and Mg phases revealed SHG responses of approximately 5.3 and 4.7 times of KDP, respectively, the order of Zn > Mg is in good agreement with the experiment data.