Noncentrosymmetric γCsIO Obtained from IO Polyhedral Rearrangements in the Centrosymmetric βPhase.

We report the synthesis and optical properties of noncentrosymmetric (NCS) γCsIO that was obtained through IO polyhedral rearrangements from centrosymmetric (CS) β-CsIO. Trifluoroacetic acid (TFA) acts as a structure-directing agent and plays a key role in the synthesis. It is suggested that the function of TFA is to promote rearrangement reactions found in the organic synthesis of stereoisomers. γCsIO crystallizes in the NCS monoclinic space group 2 (No. 4) and exhibits a strong second-harmonic-generation (SHG) response of 5.0 × KDP (KHPO) under 1064 nm laser radiation. Additional SHG experiments indicate that the material is type I phase matchable. First-principles calculations show that SHG intensity mainly comes from its , , and SHG tensor components. The synthetic strategy of discovering γCsIO provides a new way for designing novel NCS SHG materials.