Centrosymmetric RbSnF2NO3vs. noncentrosymmetric Rb2SbF3(NO3)2

Two fluoride nitrates named RbSnF2NO3 and Rb2SbF3(NO3)(2) have been successfully synthesized using a rapid evaporation concentration method by introducing Sn2+/Sb3+ cations with stereochemically active lone pairs into the nitrate system. The discrepancy in the cation sizes and coordination modes induces the different symmetries of these two title compounds, RbSnF2NO3 crystallizing in a centrosymmetric (CS) space group of C2/m, while Rb2SbF3(NO3)(2) in a noncentrosymmetric (NCS) space group of P2(1). In particular, NCS Rb2SbF3(NO3)(2) exhibits a strong second harmonic generation (SHG) response of approximately 2.7 times that of benchmark KH2PO4 (KDP) and an appropriate birefringence (0.06@1064 nm) for phase matching, indicating that Rb2SbF3(NO3)(2) is a promising UV nonlinear optical material. Detailed structural and theoretical analysis confirmed that the large nonlinear optical coefficient was derived from the synergistic effect of the pi-conjugated planar triangular NO3 groups and the Sb3+ cations with stereochemically active lone pairs.

Automated summary

Two fluoride nitrates, RbSnF2NO3 and Rb2SbF3(NO3)(2), have been successfully synthesized by introducing Sn2+/Sb3+ cations into the nitrate system. These compounds exhibit different symmetries and nonlinear optical properties, with Rb2SbF3(NO3)(2) showing promising performance in second harmonic generation.