Noncentrosymmetric Crystal [C 10 H 8 NO 2 ] 2 SiF 6 ·H 2 O with Large Birefringence.

Crystals with noncentrosymmetric structures are applied in many fields, but reported compounds have a high probability of forming a centrosymmetric structure. Here, by hydrogen-bonding the π-conjugated [C 10 H 8 NO 2 ] + cation with the separated [SiF 6 ] 2- octahedron, a noncentrosymmetric isoquinoline hexafluorosilicate monohydrate optical crystal of [C 10 H 8 NO 2 ] 2 SiF 6 ·H 2 O was formed under the regulatory influence of hydrogen bonding. It not only possesses a moderate second harmonic generation response (1.0 × KDP) but also has a large birefringence (0.282 at 550 nm), which is greater than those of most commercial birefringent crystals. In addition, the UV-vis-NIR diffuse reflectance spectrum and thermal stability analysis are also reported. Our finding gives insight into how to design noncentrosymmetric structural compounds in the organic-inorganic system.