The effects of solvent and electrolyte in the surface enhanced Raman spectrum of iron(II)bis(1,10 phenanthroline)dicyano: evidence for the formation of strong ion-pairs

The SERS (surface-enhanced Raman scattering) and SERRS (surface-enhanced resonant Raman scattering) spectra of Fe(phen)(2)(CN)(2) adsorbed on a silver electrode were investigated in different solvents and in the presence of different electrolytes. The remarkable solvatochromism and ionochromism of the complex is reflected by an outstanding dependence of the SERS spectrum on the solvent and electrolyte, particularly the relative intensity of the CN and phenanthroline modes. All evidence points to a strong interaction involving the CN moiety and the acidic protons of the solvents, besides a strong ion-pair interaction involving such moiety and cations as Li+ and Mg2+. Excitation of the SERS spectrum of Fe(phen)(2)(CN)(2) close to resonance with the high energy shoulder of the MLCT transition indicates the presence of a second charge transfer transition involving the CN moiety. (C) 1999 Elsevier Science B.V. All rights reserved.