[C(NH 2 ) 3 ][B(C 2 O 2 H 4 ) 2 ]: An Organic-Inorganic Hybrid Borate Containing Nonlinear-Optical Active Unit [B(C 2 O 2 H 4 ) 2 ] - with Solar-Blind-Region Optical Nonlinearity.

We herein report an unprecedented organic-inorganic hybrid borate incorporating a novel nonlinear-optical (NLO) active unit, namely, [C(NH 2 ) 3 ][B(C 2 O 2 H 4 ) 2 ]. The novel NLO active unit was derived from the condensation reaction between two glycol molecules and one (BO 4 ) 5- group. The title compound exhibits a moderate second-harmonic-generation effect (0.7 × KDP), a significant band gap (5.76 eV), and a suitable birefringence (0.078 at 550 nm). The optical properties are determined by the synergistic interaction between the C(NH 2 ) 3 + cation and the [B(C 2 O 2 H 4 ) 2 ] - group, as indicated by theoretical calculations.