An Optimal Arrangement of (H2C4N2O3)2- Groups in the First Non-Centrosymmetric Alkali Barbiturate Li2(H2C4N2O3)•2H2O Inducing a Giant Second Harmonic Generation Response and a Striking Birefringence

Ionic inorganic-organic ultraviolet (UV) nonlinear optical (NLO) materials have gradually become attractive because they can integrate their advantages into one. In this study, the first non-centrosymmetric alkali dihydro barbiturate, Li-2(H2C4N2O3)center dot 2H(2)O, was successfully synthesized by a mild hydrothermal method. Li-2(H2C4N2O3)center dot 2H(2)O has a short ultraviolet cutoff edge (similar to 261 nm) due to the introduction of the inorganic Li ion. Besides, owing to being nearly coplanar and the pi-conjugated organic (H2C4N2O3)(2-) groups being parallel to each other, Li-2(H2C4N2O3)center dot 2H(2)O exhibits a very strong second harmonic generation response (10.8 x KH2PO4) and a quite large birefringence (0.218@546 nm). These superior linear and nonlinear properties make Li-2(H2C4N2O3)center dot 2H(2)O a promising UV NLO material.