Single-Molecule Conductance Studies of Organometallic Complexes Bearing 3-Thienyl Contacting Groups

The compounds and complexes 1,4-C6H4(C Ccyclo-3-C4H3S)(2) (2), trans-[Pt(C C-cyclo-3-C4H3S)(2)(PEt3)(2)] (3), trans- Ru(C C-cyclo-3-C4H3S)(2)(dppe)(2)] (4) dppe = 1,2-bis(diphenylphosphino) ethane) and trans-[Ru(C C-cyclo-3C(4)H(3)S) (2){P(OEt)(3)}(4)] (5) featuring the 3-thienyl moiety as a surface contacting group for gold electrodes have been prepared, crystallographically characterised in the case of 3-5 and studied in metal | molecule | metal junctions by using both scanning tunnelling microscope break-junction (STM-BJ) and STM-I(s) methods (measuring the tunnelling current (I) as a function of distance (s)). The compounds exhibit similar conductance profiles, with a low conductance feature being more readily identified by STM-I(s) methods, and a higher feature by the STM-BJ method. The lower conductance feature was further characterised by analysis using an unsupervised, automated multi-parameter vector classification (MPVC) of the conductance traces. The combination of similarly structured HOMOs and non-resonant tunnelling mechanism accounts for the remarkably similar conductance values across the chemically distinct members of the family 2-5.