Investigation of pyridine–Ag(X), (X=NO3-,ClO4-) aqueous solutions: SERS and Raman study supported by NMR spectroscopy

The Ag–pyridine system has been investigated by Surface Enhanced Raman spectroscopy (SERS), Raman and Nuclear Magnetic Resonance (NMR) spectroscopy. Raman and NMR spectroscopy data concerning the formation of a pyridine complex with silver cations in the solution bulk have been used to explain the nature of a band at 1025 cm−1 appearing in the SERS spectrum at the anode etching of a silver electrode. The existence of two complexes of different stoichiometric composition Ag(py)+ and Ag(py)2+, has been confirmed. The distribution of pyridine forms at Ag:py mole ratios from 0 to 6 has been obtained from the analysis of the intensities of individual components of the Raman spectrum. Both types of complexes have been shown to exist in solution at equimolar 1:1 ratio. It has been assumed that a complex of 1:1 composition will be adsorbed at the excess of Ag+ ions near the surface.

► Formation of two types of complexes is possible in the Ag–pyridine aqueous system.
► At Ag:py mole ratio less then 1 Ag(py)2+ form dominates.
► At Ag:py mole ratio more then 1 Ag(py)+ form dominates.
► Band 1025 cm−1 in SERS spectrum of pyridine corresponds to adsorbed complex Ag(py)+.