SnCl2[SC(NH2)2]: lone-pair and hydrogen-bonding triggered chromophore assembling for dual optical optimization

Abstract

Designing birefringent crystals with a wide bandgap 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, a molecular crystal-SnCl₂[SC(NH₂)₂] has been screened out from crystal database. SnCl₂[SC(NH₂)₂] was characterized by a bench-shaped molecular structure, which is formed by the sharing of a 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 bandgap 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.