SURFACE-ENHANCED RAMAN-SCATTERING SPECTROSCOPY OF ORGANOMETALLICS IN SYSTEMS WITH AQUEOUS SILVER COLLOIDS

SERS (surface-enhanced Raman scattering) spectra of [Re(CO)3Br] L (L - dpp - 2,3-bis(2'-pyridyl)pyrazine, bpm = 2,2'-bipyrimidine, and bpy = 2,2'-bipyridine) complexes were investigated in systems with an aqueous Ag colloid. The organometallic species were added to the aqueous Ag colloid as solutions in dimethyl sulfoxide (DMSO). SERS spectra of DMSO and of the dpp and bpm ligands are also reported. Chemisorption of DMSO via the oxygen atom as well as co-adsorption of DMSO and of the complexes on the surface of Ag colloid was proved. The role of DMSO in formation of the SERS-active systems with the organometallics was elucidated. Good quality SERS spectra were obtained for the complexes with the tetradentate ligands L - dpp and bpm, while, for the complex with bidentate ligand L = bpy, no SERS spectra were obtained. The difference is explained by chemisorption of the complexes with L = dpp and bpm via the two uncoordinated N-atoms on the surface of Ag colloid in contrast to the absence of this interaction for the complex with L = bpy, in which the sites for chemisorption are absent. Formation of the Ag(n)+-L-Re(CO)3Br (L = dpp, bpm) heterobinuclear surface complexes is thus postulated.