Zwitterionic Glycine-Based Antimony Fluorides with Exceptional Ultraviolet Nonlinear Optical Properties

Despite significant advancements in ultraviolet nonlinear optical (UV NLO) materials, a systematic design strategy remains elusive. This study introduces an approach to enhance NLO performance by utilizing zwitterionic units. Two antimony fluoride compounds, α –2SbF 3 ·Gly and β –2SbF 3 ·Gly, were synthesized by combining glycine zwitterions with Sb 3+ cations and highly electronegative F – anions. The structure of α –2SbF 3 ·Gly belongs to the polar noncentrosymmetric space group, Ia (No. 9), while β –2SbF 3 ·Gly adopts the centrosymmetric space group, P 2 1 / c (No. 14). The metastable α –2SbF 3 ·Gly undergoes an irreversible phase transition to the thermodynamically stable polymorph, β –2SbF 3 ·Gly, at 160 °C. Notably, α –2SbF 3 ·Gly exhibits an optimized arrangement of glycine zwitterions and SbF 3 polyhedra, interconnected through hydrogen bonding. This structural configuration imparts exceptional optical properties, including a strong second-harmonic generation intensity 3.3 times that of KH 2 PO 4, a wide band gap of 4.78 eV, and a suitable birefringence of 0.146 at 546 nm, highlighting its potential as an advanced UV NLO material. This work underscores the promise of zwitterionic units as a powerful design tool for UV NLO materials, providing a foundation for the development of next-generation NLO technologies.