[RbSr 3 X][(BS 3 ) 2 ] (X = Cl, Br): two salt-inclusion thioborates with large birefringence and structure transformation from centrosymmetric to asymmetric.

[RbSr 3 X][(BS 3 ) 2 ] (X = Cl, Br), two salt-inclusion chalcogenides with planar [BS 3 ] as anionic units, were obtained. Structure analysis indicates that the size effect of halogens may adjust the arrangement between the [BS 3 ] units and further lead to the CS-to-NCS structure transformation. Experimental characterizations reveal that they have wide bandgaps (3.64-3.70 eV), large birefringence (0.136-0.144) and high LIDT (12-14 × AgGaS 2 ). This work indicates that the thioborate family is a rich source to explore structure chemistry and promising infrared functional materials.