Adsorption of Ethanediamine on Colloidal Silver: A Surface-Enhanced Raman Spectroscopy Study Combined with Density Functional Theory Calculations

The adsorption of ethanediamine on the colloidal silver surface has been studied by means of surface-enhanced Raman spectroscopy ( SERS) combined with density functional theory ( DFT) calculations. It is deduced from the SERS results that ethanediamine adsorbs on colloidal silver via its two N atoms. The calculation results suggest that the two N atoms of ethanediamine are bound to the same silver atom rather than different silver sites and ethanediamine prefers to absorb on the positively charged sites. Charge transfer between ethanediamine and the silver surface was probed by using SCN(-) as the probe molecule. The C equivalent to N stretching mode of SCN(-)adsorbed on a silver surface shifts from 2133 down to 2120 cm(-1) in the presence of ethanediamine, indicating that the charge transfer is from ethanediamine to the silver surface, which is further confirmed by DFT calculations. The ethanediamine adsorption mechanism on silver may shed light on the asymmetric catalysis involving 1,2-diamine ligands coordinated on transition metals.