Ternary Iodido Bismuthates and the Special Role of Copper.

Two new, isostructural members of the title material class, [PPh][CuBiI] (1) and [PPh][AgBiI] (2), have been prepared via a facile solution route. The crystal structure of both compounds features a tetranuclear [MBiI] (M = Cu, Ag) anion that displays an unprecedented face-sharing mode of connection between BiI octahedra and MI tetrahedra, enabling close Bi···M contacts. The two compounds allow for a direct experimental and quantum chemical investigation of the influence of group 11 metal cations on the optical and electronic properties of ternary iodido bismuthate anions, indicating that Cu is a better electronic match than Ag, resulting in a significantly lower optical band gap of the copper compound.