Structure modulation by cationic modification of sulfates using planar CS(NH2)2†

Non-centrosymmetric (NCS) structures are the prerequisite and basis for ideal nonlinear optical (NLO) crystals. However, NCS structures are usually difficult to achieve. In this regard, a cationic modulation strategy utilizing a planar molecule was proposed and implemented. With the centrosymmetric (CS) structure of ZnSO₄ as the template and planar CS(NH₂)₂ groups as a structure inducer, Zn[CS(NH₂)₂]₃SO₄ (ZTS) crystals with a NCS structure (space group of Pca2₁) were obtained, and were found to exhibit not only a large birefringence of 0.09@546 nm but also a strong second harmonic generation effect equivalent to that of KH₂PO₄ crystals. The properties of the ZTS crystals mainly result from the near uniform arrangement of the planar CS(NH₂)₂ groups. Thus, the strategy of cationic modification with planar groups contributes to both the transformation of a CS structure to a NCS structure and favorable optical properties. Therefore, this work will facilitate the development of NLO crystals, especially short-wave ultraviolet NLO crystals.