Mononuclear and dinuclear complexes of the types X(p-C6H4)C2M(diphosphine)2C2(p-C6H4)X (M = Mo, Fe, Ru; diphosphine = depe or dppe) and YM(L2)2C4M(L2)2Y (M = Fe, L2 = depe) were prepared and characterized by spectroscopic methods and exemplarily determined in their structures by X-ray diffraction studies. The X and Y groups were designed to serve as covalent or coordinative hook-ups to gold electrodes of a Controlled Break Junction device (CBJ) pursuing single molecule conductivity measurements. For the mononuclear series of molecular junctions stable anchoring was achieved with the -SC6H4- moiety originating initially from thioacetyl substitution by release of the acetyl residue upon contact with the gold electrodes. Low-bias i/V sweeps at low temperatures revealed partly strong electrical hysteresis, which according to DFT calculations were caused by redox processes and changes in the metal d-electron configurations. The dinuclear series of YFe(depe)2C4Fe(depe)2Y complexes was investigated exploring the conductivity effects of strongly covalent carbon-based anchoring groups Y = -C2-, -C4-, and in addition of coordinatively attached Y = SCN-, SeCN-, NC- moieties expecting different binding strengths to the gold surfaces. The covalent carbon binding was accomplished via Me3Sn elimination from acetylenic moieties upon contact with gold. Such covalent anchoring led to very strong binding contacts and based on the CBJ i/V measurements to very high resonant molecular conductivities with close energies of the gold Fermi level and the HOMO/LUMO levels of the complexes. The YFe(depe)2C4Fe(depe)2Y complexes with Y = coordinatively binding groups revealed for Y = CN unstable binding to the gold electrodes and for Y = SCN-, SeCN- medium binding strengths. According to the i/V sweeps of the CBJ experiments the latter cases showed electrical hystereses, which could principally be exploited for electrical switching. Concomitant DFT calculations confirmed for all the systems orbital-control for the electrode-to-electrode electron transport. The strong binding systems can thus be viewed as unique (electrode)-(junction)-(electrode) quantum mechanical molecular entities, while the medium binding stength systems with partial electronic decoupling of the junction from the gold electrodes were found to restore to a major extent the molecular properties of the junctions with their metal based various redox states and d-electron configurations.

Orbital control of single molecule conductivies and electrical switching properties of organometallic complexes

254th National Meeting (2017)

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