New Series of Polar and Nonpolar Platinum Iodates A₂Pt(IO₃)₆ (A = H₃O, Na, K, Rb, Cs)

A new series of platinum iodates, namely, α-(H3O)2Pt­(IO3)6, β-(H3O)2Pt­(IO3)6, and A2Pt­(IO3)6 (A = Na, K, Rb, Cs), have been synthesized. Interestingly, among these six stoichiometrically identical compounds, α-(H3O)2Pt­(IO3)6 is polar, whereas other compounds are nonpolar and centrosymmetric. They all consist of zero-dimensional [Pt­(IO3)6]2– molecular units separated by H3O+ or A+ cations. All of the lone electron pairs of the IO3– groups are aligned and almost point to one direction for α-(H3O)2Pt­(IO3)6, whereas IO3– groups are located trans to each other in other compounds. The material, α-(H3O)2Pt­(IO3)6, exhibits very strong second harmonic generation (SHG) effects, approximately 1.2 × KTiOPO4 (KTP), and is phase-matchable. Thermogravimetric analysis, elemental analysis, infrared spectra, UV–vis spectra, nonlinear optical properties, and theoretical calculations are also reported.