Two bismuth iodate sulfates with enhanced optical anisotropy

Abstract

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.