[SMe₃]₂[Bi₂Ag₂I₁₀], a silver iodido bismuthate with an unusually small band gap

Iodido metalates of heavy main group elements have seen much research interest in the last years due to their possible application as absorbers in photovoltaics. However, for materials based on the non-toxic element bismuth one challenge lies in narrowing the optical band gap for sufficient solar absorption. Here, we present a new iodido silver bismuthate, [SMe₃]₂[Bi₂Ag₂I₁₀] (1), which is prepared from solution and characterized regarding its structure, thermal stability and optical absorption. While compounds with similar anion compositions are known, the band gap of 1.82 eV is the smallest in chain-like Bi/Ag/I-compounds that has been reported to date. To support our experimental findings we carried out computational investigations and were able to reproduce the surprisingly narrow band gap, highlighting the subtle influence of the connectivity of different building units in multinary bismuthates. We also prepared and characterized the simple iodido pentelates [SMe]₃[E₂I₉] (E = Bi, Sb; 2, 3) to provide a point of comparison.