Single Crystalline Commensurate Metallic Assemblages of π-slabs and CdI<sub>2</sub>-Type Layers:  Synthesis and Properties of β-(EDT-TTF-I<sub>2</sub>)<sub>2</sub>[Pb<sub>5/6</sub><sub>1/6</sub>I<sub>2</sub>]<sub>3</sub> and β-(EDT-TTF-I<sub>2</sub>)<sub>2</sub>[Pb<sub>2/3+</sub><i><sub>x</sub></i>Ag<sub>1/3-2</sub><i><sub>x</sub></i><i><sub>x</sub></i>I<sub>2</sub>]<sub>3</sub>, <i>x</i> = 0.05

The ability of I···I van der Waals interactions to direct the self-assembly of slabs of the radical cation of ethylenedithio-1,2-diiodo-tetrathiafulvalene, EDT-TTF-I<sub>2</sub>, and polymeric lead iodide covalent anionic layers is demonstrated by the synthesis of single crystals of β-(EDT-TTF-I<sub>2</sub>)<sub>2</sub><sup>•+</sup>[(Pb<sub>5/6</sub>□<sub>1/6</sub>I<sub>2</sub>)<sup>1/3-</sup>]<sub>3</sub>, triclinic, P-1, <i>a</i> = 7.7818(8), <i>b </i>= 7.9760(8), <i>c</i> = 19.9668(2) Å, α = 82.409(12), β = 85.964(12), γ = 61.621(11)°, V = 1080.76(19) Å<sup>3</sup>, <i>R</i>1, w<i>R</i>2 = 0.0459, 0.0947; and β-(EDT-TTF-I<sub>2</sub>)<sub>2</sub><sup>•+</sup>[(Pb<sub>2/3+</sub><i><sub>x</sub></i>Ag<sub>1/3</sub><sub>-</sub><sub>2</sub><i><sub>x</sub></i>□<i><sub>x</sub></i> I<sub>2</sub>)<sup>1/3-</sup>]<sub>3</sub>, <i>x</i> ≈ 0.05, triclinic, P-1, <i>a</i> = 7.7744(8), <i>b</i> = 7.9193(8), <i>c</i> = 19.834(2) Å, α = 87.189(12), β = 83.534(12), γ = 61.602(11)°, V = 1067.4(2) Å<sup>3</sup>, <i>R</i>1, w<i>R</i>2 = 0.0508, 0.0997. The state-of-the-art, combined microprobe and structural analysis of the metal site vacancies and occupancies patterns reveal a commensurate organic−inorganic interface and point out the importance of halogen···halogen van der Waals interactions to future studies aiming at directing interface topologies. The electronic structure, room-temperature metallic character and metal−insulator transition at ca. 70 K of the two-dimensional organic slabs are retained upon alloying of the inorganic sublattice with monocations. The room-temperature conductivity of the metallic lead−silver alloy is 2 orders of magnitude larger than that of β<i>-</i>(EDT-TTF-I<sub>2</sub>)<sub>2</sub><sup>•+</sup>[(Pb<sub>5/6</sub>□<sub>1/6</sub>I<sub>2</sub>)<sup>1/3-</sup>]<sub>3</sub>. This calls for the study of materials with diverse alloying patterns with metal cations of different nature and charge.