Centrosymmetric RbSb(CO)(HO) and Noncentrosymmetric RbSb(CO)F: Two Antimony (III) Oxalates as UV Optical Materials.

Herein, we have successfully synthesized two rubidium antimony (III) oxalates, namely, RbSb(CO)(HO) and RbSb(CO)F, utilizing a low-temperature hydrothermal method. These two compounds share a similar chemical composition, consisting of Sb cations with active lone pair electrons, alkali metal Rb ions, and planar π-conjugated CO anions. However, they exhibit different symmetries, RbSb(CO)(HO) is centrosymmetric (CS), while RbSb(CO)F is noncentrosymmetric (NCS), which should be caused by the presence of F ions. Notably, the NCS compound, RbSb(CO)F, demonstrates a moderate second-harmonic generation (SHG) response, approximately 1.3 times that of KHPO (KDP), and exhibits a large birefringence of 0.09 at 546 nm. These characteristics indicate that RbSb(CO)F holds promising potential as a nonlinear optical material for ultraviolet (UV) applications. Detailed structural analysis and theoretical calculations confirm that the excellent optical properties arise from the synergistic effects between Sb cations with SCALP and planar π-conjugated [CO] groups.