Explorations of a Series of Second Order Nonlinear Optical Materials Based on Monovalent Metal Gold(III) Iodates

The syntheses, crystal structures, and characterizations of a series of monovalent metal gold­(III) iodates, namely, α-NaAu­(IO3)4, β-NaAu­(IO3)4, RbAu­(IO3)4, α-CsAu­(IO3)4, β-CsAu­(IO3)4, and AgAu­(IO3)4 are reported. Their structures feature Au­(IO3)4– anions that are separated by alkali metal ions or silver­(I) ions. The Au­(IO3)4– anions in the polar α-NaAu­(IO3)4, RbAu­(IO3)4, and α-CsAu­(IO3)4 are polar with all four iodate groups being located only above (or below) the AuO4 square plane (cis- configuration). α-NaAu­(IO3)4, RbAu­(IO3)4, and α-CsAu­(IO3)4 display moderate strong Second-Hamonic Generation (SHG) responses of 1.17 ×, 1.33 ×, and 1.17 × KTP (KTiOPO4), respectively, and all three materials are type-I phase-matchable. The Au­(IO3)4– anions in centrysymmetric β-NaAu­(IO3)4, β-CsAu­(IO3)4, and AgAu­(IO3)4 are nonpolar with the four iodate groups of the Au­(IO3)4– anion being located both above and below the AuO4 square plane (trans- configuration). IR and UV spectra, luminescent and ferroelectric properties have also been measured. Theoretical calculations of their optical properties based on density functional theory (DFT) methods were performed by using the CASTEP total-energy code.