Synthesis, Structure and Physical Properties of “Wire-like” Metal Complexes

The syntheses and crystallographically determined structures of metal complexes trans-[M(C≡CR)2Ln] (MLn = Ru(dppe)2, Ru{P(OEt)3}4, Pt(PEt3)2) featuring acetylide ligands further functionalized by aryl thioether groups are reported, together with those of analogous organic buta-1,3-diyne (RC≡CC≡CR) and 1,4-diethynylbenzene (RC≡CC6H4C≡CR) compounds for comparative purposes. The terminal thioether functional groups have an affinity for binding to the surface of gold electrodes and are considered as “anchor” groups in the design of molecules for study within metal|molecule|metal molecular junctions. The influence of the Lewis acidic and π-basic thioether moiety on a number of physical properties important to the electrical behavior of molecules within molecular junctions has been explored using spectroscopic, electrochemical, and quantum chemical methods. The thioether functional group serves as a moderately strong π-electron-donating substituent, similar in electronic character to the OMe group, resulting in relatively high lying HOMOs that are delocalized over the length of the molecule and well-suited to promote coherent tunneling within the junction. In addition, the facile oxidation processes and the relatively small reorganization energies associated with the one-electron oxidation of these compounds indicate the potential for effective hopping mechanisms of charge transport through longer structures based on these organometallic motifs.