The Weak 3D Topological Insulator Bi(12)Rh(3)Sn(3)I(9)

Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation‐free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well‐characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth‐based subiodides and recently succeeded in synthesizing a new compound Bi(12)Rh(3)Sn(3)I(9), which is structurally closely related to Bi(14)Rh(3)I(9) – a stable, layered material. In fact, Bi(14)Rh(3)I(9) is the first experimentally supported weak 3D TI. Both structures are composed of well‐defined intermetallic layers of (∞) (2)[(Bi(4)Rh)(3)I](2+) with topologically protected electronic edge‐states. The fundamental difference between Bi(14)Rh(3)I(9) and Bi(12)Rh(3)Sn(3)I(9) lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi(14)Rh(3)I(9) are isolated by (∞) (1)[Bi(2)I(8)](2−) chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to (∞) (2)[Sn(3)I(8)](2−) layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity.