SnCl2[SC(NH2)2]: Lone-Pair and Hydrogen-Bonding Triggered Chromophore Assembling for Dual Optical Optimization

Designing birefringent crystals with wide band gap presents significant challenges, especially within chalcogenide systems. Herein, motivated by the high structural anisotropy of thiourea, along with the ultraviolet compatibility and birefringence activity of halogenated tin(II)-based anionic groups, SnCl2[SC(NH2)2], a novel molecular crystal, was discovered. SnCl2[SC(NH2)2] was characterized by a bench-shaped molecule structure which is formed by the sharing of sulfur anion between a distorted SnCl2S trigonal pyramid and a planar π-conjugated thiourea unit. Through the synergistic interactions among multiple functional groups and the auxiliary regulation of hydrogen bonds, SnCl2[SC(NH2)2] succeeded in breaking the “3 eV wall” with a band gap of 3.362 eV and achieved a large birefringence of 0.20@546 nm, demonstrating a facile design strategy for the development of chalcogenides with dual optical enhancement.