Metal Methanesulfonates with Mixed Anionic Groups with Large Band Gaps and Enhanced Birefringence

Four new metal methanesulfonates with mixed anionic groups, Bi(SeO3)(CH3SO3) (1), Bi(TeO3)(CH3SO3) (2), Ba(BF4)(CH3SO3) (3), and Ba-2(BF4)(CH3SO3)(3)(H2O)(3) (4), have been successfully synthesized. Compounds 1 and 2 are isomorphic and exhibit a two-dimensional (2D) layered structure. Stereoactive lone pairs are observed with Se4+, Te4+, and Bi3+. Compound 3 features a three-dimensional (3D) structure formed by connecting [Ba(CH3SO3)](+) layers via BF4 tetrahedra, whereas compound 4 features a 2D layered structure, where the BF4 tetrahedra are positioned on both sides of the [Ba-2(CH3SO3)(3)](+) layers. The ultraviolet-visible-near-infrared (UV-vis-NIR) spectra indicate that compounds 1 and 2 have absorption edges at 270 and 274 nm, whereas compounds 3 and 4, with absorption edges below 200 nm, are characterized as deep-UV crystals. Calculations were performed to determine the absorption edges, and comparative analysis indicates a significant enhancement in the calculated birefringence values compared to analogous compounds.