In situ vibrational spectroscopy of contact adsorbed thiocyanate on silver electrodes: experiment and theory

Abstract

In situ Fourier transform infrared vibrational spectra of thiocyanate ions adsorbed on polycrystalline Ag electrodes as a function of electrode potential and electrolyte concentration are reported. Interpretation of the results are performed with the help of ab initio SCF calculations of the electronic structure and bonding of thiocyanate to small silver clusters. It was concluded that thiocyanate ion adsorbs with S-and N-end down in the double layer region for potentials greater than -0.3 V (versus Ag/AgCl). At potentials close to the potential of zero charge thiocyanate ion is adsorbed flat and cannot be detected by IR.

Electrochemical Contact Adsorption Site Changes Driven by Field and Charge: Fact and Theory

“…These have been interpreted as adsorption with S-and N-atom down in accordance with correlations known between crystal structure and ir spectra of inorganic coordination complexes [51]. Cluster calculations for Agn (n = 1, 5 and 10) show there to be two possible orientations [50,52]. N down has the configuration axis perpendicular to the surface plane, whereas S-down lies almost flat.…”

“…Both sers and surface ftir show the presence of multiple bands in the region of the, internal C-N stretching mode at ca.2000 cm-I [49,50]. These have been interpreted as adsorption with S-and N-atom down in accordance with correlations known between crystal structure and ir spectra of inorganic coordination complexes [51].…”

Potential-Dependent Reorientation of Thiocyanate on Au Electrodes

“…4 SCN forms bond with the metals via the S or N end, 5 via both ends in bridge form, 6 and also in three-waybridging M 2 SCN-M′ geometry. 7 Because of its strong adsorption on metal surface and the large infrared and Raman cross section of the C-N stretch, thiocyanate has been studied extensively by in situ vibrational spectroscopies [8][9][10][11] such as confocal microprobe Raman spectroscopy (CMR), 10 surface-enhanced Raman spectroscopy (SERS), 12 potential-difference infrared spectroscopy (PDIR), 13,14 polarization-modulation reflection absorption infrared spectroscopy (PM-RAIRS), 15 attenuated total internal reflection infrared spectroscopy (ATR), 16 and sum-frequency generation (SFG). 17,18 The frequency of the C-N stretch is sensitive to both the adsorption geometry and the electrode potential via the Stark effect.…”

Adsorption of thiocyanate on polycrystalline silver and gold electrodes studied in situ by sum-frequency spectroscopy

“…The adsorption of thiocyanate (SCN-) onto the surfaces of silver and gold has been something of a testing ground for in situ vibrational spectroscopy in recent years. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Thiocyanate has a rich homogeneous coordination chemistry.17 It binds readily to most complex-forming metal ions through the nitrogen atom, the sulfur atom, or both. The sulfur atom can also form a bridge between two metal ions.…”