High-conductive organometallic molecular wires with delocalized electron systems strongly coupled to metal electrodes

Besides active, functional molecular building blocks such as diodes or switches, passive components, for example, molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule-metal coupling on charge transport of dinuclear X(PP)₂FeC₄Fe(PP)₂X molecular wires (PP = Et₂PCH₂CH₂PEt₂); X = CN (1), NCS (2), NCSe (3), C₄SnMe₃ (4), and C₂SnMe₃ (5) under ultrahigh vacuum and variable temperature conditions. In contrast to 1, which showed unstable junctions at very low conductance (8.1 × 10^-7 G₀), 4 formed a Au-C₄FeC₄FeC₄-Au junction 4′ after SnMe₃ extrusion, which revealed a conductance of 8.9 × 10^-3 G₀, 3 orders of magnitude higher than for 2 (7.9 × 10^-6 G₀) and 2 orders of magnitude higher than for 3 (3.8 × 10^-4 G₀). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C-Au coupling case enables the delocalized electronic system of the organometallic Fe₂ backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires.