Synergism of [C 2 N 4 H 7 S] cations and anionic modulators: tailoring second-order nonlinear optics and birefringence in organic–inorganic crystals

High-performance UV NLO crystals based on the [C 2 N 4 H 7 S] cation were realized by anion selection: NCS (C 2 N 4 H 7 S)SO 3 NH 2 gives 1.8 × KDP SHG, while CS (C 2 N 4 H 7 S)BF 4 shows large birefringence (0.500@546 nm).