THE EFFECT OF LIGAND STRUCTURE ON SURFACE-ENHANCED RAMAN-SCATTERING BY FE(II) MACROCYCLIC COMPLEXES - [(FETPC)-T-II](2-D-II](2+)() AND [(FEDPC))

This paper reports studies on surface-enhanced Raman scattering (SERS) by two ferrous macrocyclic complexes, one with the pentadentate ligan d, DPC (DPC = N,N'-di-2-picolyl-4,7-diaza-1-oxacyclononane), and the o ther with the hexadentate ligand, TPC (TPC = N,N',N ''-tri-2-picolyl-1 ,4,7-triazacyclononane). The purpose of this work is to show how the l igand structure changes Raman scattering by the Fe(II) complexes on a silver hydrosol protected by sodium citrate, Ag/Cit(3-). It is demonst rated that SERS by [(FeTPC)-T-II](2+) on Ag/Cit(3-) is enhanced by the factor of E = 3.5 +/- 0.5 +/- 10(3), if the concentration of the sol is live times that of the complex. However, the relative intensities a nd frequencies in the SERS spectrum are parallel to those obtained upo n resonance Raman experiments with lambda(ex) = 441.2 nm. In contrast to [(FeTPC)-T-II](2+), Raman scattering by [(FeDPC)-D-II](2+) on Ag/Ci t(3-) is quite different to that obtained from the aqueous solution wi th no silver sol, and includes resonance Raman-forbidden modes. These observations are considered in terms of the electromagnetic and chemic al mechanisms of surface-enhanced Raman scattering. It is postulated t hat the chemical mechanism is predominant in Raman scattering by the [ (FeDPC)-D-II](2+) complex with the open coordination site on the Fe(II ) cation, whereas the electromagnetic mechanism provides a better fit to the behavior of [(FeTPC)-T-II](2+) on Ag/Cit(3-), as there is no op portunity for an Ag-[(FeTPC)-T-II](2+) surface complex formation.