The single-molecule conductance of metal complexes of the general forms trans-Ru(CCArC CY) 2 (dppe) 2 and trans-Pt(CCArCCY) 2 (PPh 3 ) 2 (Ar = 1,4-C 6 H 2 -2,5-(OC 6 H 13 ) 2 ; Y = 4-C 5 H 4 N, 4-C 6 H 4 SMe) have been determined using the STM I(s) technique. The complexes display high conductance (Y = 4-C 5 H 4 N, M = Ru (0.4 ± 0.18 nS), Pt (0.8 ± 0.5 nS); Y = 4-C 6 H 5 SMe, M = Ru (1.4 ± 0.4 nS), Pt (1.8 ± 0.6 nS)) for molecular structures of ca. 3 nm in length, which has been attributed to transport processes arising from tunneling through the tails of LUMO states.

and break-off distance data, we demonstrate that a PPh 3 supporting ligand in the platinum complexes can provide an alternative contact point for the STM tip in the molecular junctions, orthogonal to the terminal CuCSiMe 3 group. The attachment of hexyloxy side chains to the diethynylbenzene ligands, e.g. trans-Pt{CuCC 6 H 2 (Ohex) 2 CuCSiMe 3 } 2 (PPh 3 ) 2 (Ohex = OC 6 H 13 ), hinders contact of the STM tip to the PPh 3 groups and effectively insulates the molecule, allowing the conductance through the full length of the backbone to be reliably measured. The use of trialkylphosphine (PEt 3 ), rather than triarylphosphine (PPh 3 ), ancillary ligands at platinum also eliminates these orthogonal contacts. These results have significant implications for the future design of organometallic complexes for studies in molecular junctions.

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