Surface-enhanced vibrational study of azabipiridyl and its Co(II), Ni(II) and Cu(II) complexes

The FT-Raman spectra and surface-enhanced Raman scattering (SERS) on silver colloid of the azabipiridyl ligand and its Co(Ii), Ni(Il) and Cu(II) compl exes are reported. A resonance Raman (RR) study of the solids and a surface -enhanced infrared absorption (SEIRA) study were also accomplished. The spe ctral analysis indicates that there is a remarkable enhancement of the Rama n spectra induced by the presence of an Ag surface. The complex-surface int eraction is verified by the appearance of a v(Ag-N) band at about 216 cm(-1 ). A general energy increasing of most of the molecular modes by surface ef fect is associated to a charge transfer from the colloidal silver surface, thus, leading to an important contribution of the charge transfer mechanism to the SERS enhancement, which is corroborated by the resonant effect obse rved at different excitation lines. From the analysis of the SERS spectra a preferential planar parallel orientation of the complexes on the surface i s deduced, in such a way that all the complexes tend to adopt a similar str ucture when they are adsorbed on the metal surface. On the contrary, the ma crocycle ligand is oriented tilted, face-on to the surface. The SEIRA study of the compounds deposited onto Au films reveals slight structural modific ations upon dilution. The spectral analysis was completed with a semiempiri cal calculation and a normal co-ordinate analysis. (C) 2001 Elsevier Scienc e B.V All rights reserved.