Nonlinear Optical Effects of Hybrid Antimony(III) Halides Induced by Stereoactive 5s2 Lone Pairs and Trimethylammonium Cations

Organic–inorganic hybrid metal halides have unique optical and electronic properties, which are advantageous in the study of nonlinear optical materials. To investigate the effect of stereoactive lone pair electrons and the induction of organic cations on the structure of hybrid antimony(III) halides on nonlinear optics, we synthesize two noncentrosymmetric hybrid antimony(III)-based halide single crystals (TMA) 3 Sb 2 X 9 (TMA = NH(CH 3 ) 3 +, X = Cl, Br) by a room-temperature slow evaporation method, and their single-crystal structures, phase transition, X-ray photoelectron spectroscopy, and energy-band structure calculations are studied. More importantly, second-harmonic generation results of (TMA) 3 Sb 2 X 9 (X = Cl, Br) are about 0.7 and 0.8 × KH 2 PO 4 (KDP), respectively. Interestingly, (TMA) 3 Sb 2 Cl 9 single crystals undergo a reversible structural transition from Pc (No. 7) at room temperature to P 2 1 / c (No. 14) at 400 K, while the (TMA) 3 Sb 2 Br 9 single crystals belong to the noncentrosymmetric space group R 3c (No. 161), which clarifies the previous results. This work not only deepens the understanding of the role in lone pair electrons and organic cations in the structural induction in antimony-based halide perovskite materials but also provides guidance for subsequent nonlinear optical explorations.