Two bismuth iodate sulfates with enhanced optical anisotropy.

Two bismuth iodate sulfates crystallizing in the monoclinic space group 2/, namely, Bi(IO)(SO) and CdBi(IO)(SO), were synthesized solvothermal reactions. Bi(IO)(SO) features 2D [Bi(SO)] layers, which are further linked by the IO groups to form a 3D network. CdBi(IO)(SO) exhibits 1D [IO] chains built from IO groups corner-sharing and is the first example of a polyiodate sulfate as far as we know. These [IO] chains are interconnected by Bi cations into [Bi(IO)] layers parallel to the plane, whereas the neighbouring Cd cations are interconnected by bridging SO anions into [Cd(SO)] layers, also parallel to the plane. These cationic and anionic 2D layers are held together through Bi-O-S bridges into a complicated 3D framework. Bi(IO)(SO) and CdBi(IO)(SO) 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 Bi, into metal sulfates can greatly enhance their birefringent properties.