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.