SERS OF THE BIS(4,5-DIMERCAPTO-1,3-DITHIOLE-2-THIONATO) NICKELATE(III) COMPLEX ION AND OF ITS INCLUSION COMPOUND IN GAMMA-CYCLODEXTRIN ADSORBED ON A SILVER ELECTRODE

The surface-enhanced Raman (SER) spectra of the complex [Ni(dmit)2]- ( H-2dmit = 4,5-dimercapto-1,3-dithiole-2-thione) adsorbed on a silver e lectrode have been investigated in two different ways, first from a so lution containing the dissolved complex and second from a solution con taining the Ni(III) complex included in gamma-cyclodextrin (gamma-CD). In the first case and for the applied potentials investigated the SER spectra present several features that were assigned to the Ni(II) com plex adsorbed flat on the electrode surface. When the Ni(III) complex is included in gamma-CD only one feature is observed in the SER spectr a at ca. 230 cm-1, which is assigned to the nu(Ag-S) mode of the inclu sion compound adsorbed head-on via the sulfur atom of the C=S moiety t owards the silver surface. These results have shown that when the comp lex adsorbs flat the charge-transfer mechanism (metal --> adsorbate) o f enhancement plays a role for the total enhancement while in the case of the adsorbed inclusion compound the charge-transfer mechanism is o f the type adsorbate --> metal.