Deep Eutectic Solvents Synthesis of A₂Sb(C₂O₄)Cl₃ (A = NH₄, K, Rb) with Superior Optical Performance

Abstract Deep eutectic solvents (DESs), which are considered as a new kind of green solvents, have been adopted for the synthesis of diverse functional materials. Herein, DESs synthesis is used to solve the problem of easy hydrolysis and oxidation of the emerging optical functional groups Sb³⁺ cations, producing three novel antimony chloride oxalates named A₂Sb(C₂O₄)Cl₃ (A = NH₄, K, Rb). The three title compounds feature noncentrosymmetric structures consisted of [Sb(C₂O₄)Cl₃]^2– anionic clusters, which induce excellent linear and nonlinear optical properties of them. Particularly, Rb₂Sb(C₂O₄)Cl₃ exhibits a strong nonlinear optical response that is 2.1 times that of KH₂PO₄, as well as large calculated birefringence of 0.22@546 nm, indicating that antimony oxalates are promising optical materials. This work affords an effective strategy to settle the difficulties in crystallization of the materials including cations with low oxidation state and easy hydrolysis.