Sb 4 O 3 (TeO 3 ) 2 (HSO 4 )(OH): An Antimony Tellurite Sulfate Exhibiting Large Optical Anisotropy Activated by Lone Pair Stereoactivity.

A new birefringent crystal of Sb 4 O 3 (TeO 3 ) 2 (HSO 4 )(OH) was achieved by incorporating two stereochemically active lone pair (SCALP) cations of Sb(III) and Te(IV) into sulfates simultaneously. The Sb 3+ and Te 4+ ions display highly distorted coordination environments due to the SCALP effect. Sb 4 O 3 (TeO 3 ) 2 (HSO 4 )(OH) displays a 3D structure composed of [Sb 4 O 3 (TeO 3 ) 2 (OH)] ∞ + layers bridged by [SO 3 (OH)] - tetrahedra. It possesses a large birefringence and a wide optical transparent range, making it a new UV birefringent crystal. First-principles calculation analysis suggests that the synergistic effect of the cooperation of SCALP effect of Sb 3+ and Te 4+ cations make a dominant contribution to the birefringence. The work highlights that units with SCALP cations have advantages in generating large optical anisotropy and are preferable structural units for designing novel birefringent materials.