Two bismuth iodate sulfates with enhanced optical anisotropy

Two bismuth iodate sulfates crystallizing in the monoclinic space group P21/c, namely, Bi(IO3)(SO4) and CdBi(IO3)(SO4)2, were synthesized via solvothermal reactions. Bi(IO3)(SO4) features 2D [Bi(SO4)]+ layers, which are further linked by the IO3- groups to form a 3D network. CdBi(IO3)(SO4)2 exhibits 1D [IO3]- chains built from IO43- groups via corner-sharing and is the first example of a polyiodate sulfate as far as we know. These [IO3]- chains are interconnected by Bi3+ cations into [Bi(IO3)]2+ layers parallel to the bc plane, whereas the neighbouring Cd2+ cations are interconnected by bridging SO42- anions into [Cd(SO4)2]2- layers, also parallel to the bc plane. These cationic and anionic 2D layers are held together through Bi-O-S bridges into a complicated 3D framework. Bi(IO3)(SO4) and CdBi(IO3)(SO4)2 show wide band gaps of 3.91 and 4.03 eV and large birefringence values of 0.087 and 0.100 at 1064 nm, respectively. Our work indicates that the introduction of iodate group and lone pair cations, such as Bi3+, into metal sulfates can greatly enhance their birefringent properties.