[C(NH₂)₃][B(C₂O₂H₄)₂]: An Organic–Inorganic Hybrid Borate Containing Nonlinear-Optical Active Unit [B(C₂O₂H₄)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(NH2)3][B(C2O2H4)2]. The novel NLO active unit was derived from the condensation reaction between two glycol molecules and one (BO4)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(NH2)3+ cation and the [B(C2O2H4)2]− group, as indicated by theoretical calculations.