High-Conductive Organometallic Molecular Wires with De localized 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 moleculemetal coupling on charge transport of dinuclear X(PP)(2)FeC4Fe(PP)(2)X 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 x 10 (7) G(0)), 4 formed a AuC4FeC4FeC4Au junction 4' after SnMe3 extrusion, which revealed a conductance of 8.9 x 10 (3) G(0), 3 orders of magnitude higher than for 2 (7.9 x 10 (6) G(0)) and 2 orders of magnitude higher than for 3 (3.8 x 10 (4) G(0)). 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 CAu coupling case enables the delocalized electronic system of the organometallic Fe-2 backbone to be extended over the moleculemetal interfaces to the metal electrodes to establish high-conductive molecular wires.