Noncentrosymmetric γ - Cs 2 I 4 O 11 Obtained from IO 4 Polyhedral Rearrangements in the Centrosymmetric β - Phase.

We report the synthesis and optical properties of noncentrosymmetric (NCS) γ - Cs 2 I 4 O 11 that was obtained through IO 4 polyhedral rearrangements from centrosymmetric (CS) β-Cs 2 I 4 O 11 . 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. γ - Cs 2 I 4 O 11 crystallizes in the NCS monoclinic space group P 2 1 (No. 4) and exhibits a strong second-harmonic-generation (SHG) response of 5.0 × KDP (KH 2 PO 4 ) 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 d 34 , d 21 , and d 23 SHG tensor components. The synthetic strategy of discovering γ - Cs 2 I 4 O 11 provides a new way for designing novel NCS SHG materials.