[C(NH 2 ) 2 NHNO 2 ][C(NH 2 ) 3 ](NO 3 ) 2 : A Mixed Organic Cationic Hybrid Nitrate with an Unprecedented Nonlinear-Optical-Active Unit.

We herein report a mixed organic cationic hybrid nitrate, namely, [C(NH 2 ) 2 NHNO 2 ][C(NH 2 ) 3 ](NO 3 ) 2 ( 1 ). It was successfully achieved via combining three different planar groups: [(C(NH 2 ) 2 NHNO 2 ] + , C(NH 2 ) 3 + , and NO 3 - . First-principles calculations confirm that the [(C(NH 2 ) 2 NHNO 2 ] + group is an excellent cationic nonlinear-optical (NLO)-active unit. The title compound exhibits a moderate second-harmonic-generation (SHG) response (1.5 × KDP), a wide band gap (3.58 eV), and a suitable birefringence of 0.071 at 550 nm. Theoretical calculations indicate that the synergy effect between the [(C(NH 2 ) 2 NHNO 2 ] + and C(NH 2 ) 3 + groups dominates the SHG process.