The bismuth-rich subiodides Bi[IrBi₆I₁₂], Ag₃[IrBi₆I₁₂], and Bi_xCu_3–3x[IrBi₆I₁₂] were synthesized by high-temperature reactions in sealed silica ampules and characterized by powder and single-crystal X-ray diffraction, differential scanning calorimetry, energy-dispersive X-ray spectroscopy, and density functional theory (DFT) calculations. All three compounds contain cuboctahedral [IrBi₆I₁₂]³⁻ cluster anions composed of an iridium-centered bismuth octahedron with iodide-bridged edges, but differ markedly in the occupation of the octahedral voids of the underlying rock-salt-related packing. In Bi[IrBi₆I₁₂], the clusters are linked by Bi³⁺ cations into infinite chains. Ag₃[IrBi₆I₁₂] adopts a rock-salt-related superstructure with a high degree of occupation of octahedral voids by Ag⁺ and thus represents the most densely interconnected member of this cluster family known so far. At room temperature, the silver substructure is strongly disordered and gives rise to an ionic conductivity of 1.05 × 10⁻⁴ S cm⁻¹, whereas at 100 K a commensurately modulated fivefold superstructure reveals long-range silver ordering. Attempts to prepare the corresponding copper compound “Cu₃[IrBi₆I₁₂]” were unsuccessful; instead, a phase with a homogeneity range, Bi_xCu_3–3x[IrBi₆I₁₂] with x ≥ 0.5, was obtained, in which Bi³⁺ is replaced by Cu+ distributed over trigonal-planar and tetrahedral sites in and around the corresponding octahedral voids. Electron-counting considerations and DFT-based bonding analyses consistently support an electron-precise 18-electron configuration for iridium in [IrBi₆I₁₂]³⁻. DFT calculations identify Bi[IrBi₆I₁₂] and Ag₃[IrBi₆I₁₂] as narrow-gap semiconductors.