Chiral amino acid-templated tin fluorides tailoring nonlinear optical properties, birefringence, and photoluminescence

Abstract

In this study, we successfully synthesized two types of new chiral amino acid-templated tin fluoride crystals: (R)-[(C₈H₁₀NO₃)₂]Sn(IV)F₆, (S)-[(C₈H₁₀NO₃)₂]Sn(IV)F₆, (R)-[C₈H₁₀NO₃]Sn(II)F₃, and (S)-[C₈H₁₀NO₃]Sn(II)F₃, employing a slow evaporation method. The crystal structures of Sn(IV)-compounds were determined to belong to the noncentrosymmetric (NCS) nonpolar space group, P2₁2₁2. Conversely, the structures of Sn(II)-compounds were found to crystallize in the NCS polar space group, P2₁, as revealed by single-crystal X-ray diffraction analysis. Remarkably, Sn(IV)-compounds exhibited a larger birefringence (0.328@546.1 nm), attributed to the well-stacked arrangement of planar π-conjugated benzene rings along the b-axis. The ability of tin(IV) fluorides to form more hydrogen bonds with ligands increased the probability of π–π interactions between benzene rings, enabling the growth of centimeter-sized crystals in Sn(IV)-compounds. In contrast, Sn(II)-compounds displayed a stronger second-harmonic generation (SHG) response (0.85 × KDP) than Sn(IV)-compounds (0.46 × KDP). This enhanced SHG response in Sn(II)-compounds was attributed to the increased dipole moments resulting from the presence of lone pairs. Additionally, Sn(II)-compounds exhibited photoluminescent properties due to the transition from the metal-to-ligand charge transfer state, facilitated by the presence of the lone pairs.