Ternary Iodido Bismuthates and the Special Role of Copper

Two new, isostructural members of the title material class, [PPh₄]₄[Cu₂Bi₂I₁₂] (1) and [PPh₄]₄[Ag₂Bi₂I₁₂] (2), have been prepared via a facile solution route. The crystal structure of both compounds features a tetranuclear [M₂Bi₂I₁₂]^4- (M = Cu, Ag) anion that displays an unprecedented face-sharing mode of connection between BiI₆ octahedra and MI₄ 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.