Studies of organometallic self-assembled monolayers on Ag and Au using surface plasmon spectroscopy

We report the synthesis of a novel rhenium complex, {fac-Re(2,2'-bipyridine)(CO)(3)(NC5H4)CH2NHCO(CH2)(2)S-}(2) and its self-assembly behavior on Ag and Au, including characterization of the monolayer using surface plasmon spectroscopy (SPS). Further surface characterization, which proved to be quite complementary to SPS, was accomplished with surface-enhanced Raman spectroscopy (SERS), FTIR, ellipsometry, and contact angle measurements. SERS and FTIR data have also been used to verify the self-assembly of the free ligand and rhenium complexes on Ag to form monolayers (SAMs). Vibrational analysis also provided evidence that the attachment of the free ligand and complexes to the metal substrate occurs by reaction of the disulfide bond and not through the pyridine or bipyridine. The tilt angle of the complex with respect to the surface normal of the metal was also calculated using a projection analysis that incorporated the SPS determined thickness and a molecular mechanics (MM) minimized molecular length. Independently, a MM tilt angle was determined by minimization of a hexagonal grouping of six complexes surrounding one, each bound through a sp hybridized S-metal bond to a hollow surface site. Though this calculation is in need of further refinement, the agreement with our projection analysis is good.