Explorations of New Second-Order Nonlinear Optical Materials in the Potassium Vanadyl Iodate System

Four new potassium vanadyl iodates based on lone-pair-containing IO3 and second-order Jahn-Teller distorted VO5 or VO6 asymmetric units, namely, alpha-KVO2(IO3)(2)(H2O) (Pbca), beta-KVO2(IO3)(2)-(H2O) (P2(1)2(1)2(1)), K-4[(VO)(IO3)(5)](2)(HIO3)(H2O)(2)center dot H2O (PI), and K(VO)(2)O-2(IO3)(3) (Ima2) have been successfully synthesized by hydrothermal reactions. alpha-KVO2(IO3)(2)(H2O) and beta-KVO2(IO3)(2)(H2O) exhibit two different types of ID [VO2(IO3)(2)](-) anionic chains. Neighboring VO6 octahedra in the alpha-phase are corner-sharing into a ID chain with the IO3 groups attached on both sides of the chain in a uni- or bidentate bridging fashion, whereas those of VO5 polyhedra in the beta-phase are bridged by IO3 groups into a right-handed helical chain with remaining IO3 groups being grafted unidentately on both sides of the helical chain. The structure of K-4[(VO)(IO3)(5)](2)(HIO3)(H2O)(2)center dot H2O contains novel isolated [(VO)(IO3)(5)](2-) units composed of one VO6 octahedron linked to five IO3 groups and one terminal O2- anion. The structure of K(VO)(2)O-2(IO3)(3) exhibits a ID [(VO)(2)O-2(IO3)(3)](-) chain in which neighboring VO6 octahedra are interconnected by both oxo and bridging iodate anions. Most interestingly, three of four compounds are noncentrosymmetric (NCS), and K(VO)(2)O-2(IO3)(3) displays a very strong second-harmonic generation response of about 3.6 x KTP, which is phase matchable. It also has high thermal stability, a wide transparent region and moderate hardness as well as an excellent growth habit. Thermal analyses and optical and ferroelectric properties as well as theoretical calculations have also been performed.