(C13N3H14)2MBr4 (M = Zn, Cd): two novel hybrid metal halides with balanced integrated nonlinear optical performance†

The design and synthesis of high-performance nonlinear optical (NLO) crystals is a critical but intractable challenge in the development of advanced lasers technology. Herein, two novel zero-dimensional hybrid metal halides, namely, (C₁₃N₃H₁₄)₂ZnBr₄ (1) and (C₁₃N₃H₁₄)₂CdBr₄ (2), were successfully synthesized through a mild solution method. They crystalize in the orthorhombic noncentrosymmetric Pna2₁ space group. Both 1 and 2 exhibit good comprehensive NLO properties, including phase matchable and strong SHG effect (1.12× and 0.98 × KH₂PO₄), wide bandgaps (3.96 and 3.98 eV), large birefringences (0.15 and 0.12@1064 nm), and high laser-induced damage thresholds (28× and 25 × AgGaS₂), suggesting that they are promising NLO materials. In addition, the theoretical studies and crystal structure analysis reveal that their SHG responses and birefringences originate from the synergism of the ordered alignment of organic cations as well as the distorted [MX₄] (M = Zn, Cd) tetrahedra. This work provides a new paradigm for designing and synthesizing high-performance NLO materials.