Fully X-substituted C222-X, Si222-X, and Ge222-X structures are sampled using RDKit as described in Supporting Information part A. Common to all the methylthiomethyl-functionalized bicyclo[2.2.2]-systems, the molecular core is chiral but has no conformational freedom. Therefore, the orientations of the two linkers relative to each other provide three conformations. These are shown in Figure as a Newman projection along the bridgehead axis of the molecule, and as the optimized conformations of Si222-H. It is the Si-Si-CH 2 -S dihedral angles of the linkers that must be rotated to sample the three conformations. In accordance with previous work, we refer them as the anti, ortho, and cis conformers. We sample these three in all studied molecules. For a control system, we examine the equivalent linear molecule in its all-trans conformation as shown in bottom panel of Figure . All structures are optimized using density functional theory as implemented in Gaussian09 using the PBE exchange-correlation (XC) functional with 6-311G(d,p) basis set. Single-molecule junctions were made by placing the optimized molecules between two four-atom Au pyramids on 5x5 Au fcc(111) surfaces. The initial junction structure is built using Au-S bond length of 2.5 Å and Au-S-C bond angle of 110°. The terminal methyl groups are rotated to a dihedral angle of ±90° in order to make space for the Au atoms in the transoid position (±170°). Junctions are relaxed to a force threshold of 0.06 eV/Å using DFT with the PBE XC functional and double-z plus polarization basis set as implemented in ASE and GPAW. Finally, the Landauer transmission is calculated using the NEGF approach as implemented in ASE. We devise an extensive list of substituents based on the criterion of some extent of chemical realism, though in some cases also on chemical curiosity. The different substituents on C222-X, Si222-X, and Ge222-X are to some extent limited by the size of the molecular frame, and therefore not all substituents can be used. Scheme 1 provides an overview of all 34 molecules studied.