Bi(SO)F·HO and Bi(SO)(NO)·3HO: Chemical Substitution-Induced Birefringence Enhancement in Bismuth Sulfates.

Two new Bi(III)-based sulfates, namely, Bi(SO)F·HO (BSOF) and Bi(SO)(NO)·3HO (BSNO), have been successfully synthesized through aliovalent replacement of partial [SO] groups with F and [NO] anions, respectively, in the parent structure of Bi(SO). Such chemical replacement altered the coordination environment of Bi cations, facilitating changes in the structure and optical properties. Notably, the birefringence values of BSOF and BSNO are found to be 4.4 and 15.5 times that of parent Bi(SO). Further investigation into the structure-property relationship revealed that the birefringence enhancement in BSOF and BSNO is attributed to the improvement of the polarizability anisotropy of Bi-centered polyhedra in BSOF and BSNO compared to that of Bi(SO). In addition, the existence and optimized arrangement of planar [NO] groups are also indispensable for further birefringence improvement of the BSNO compound.