Unique adsorbed state of 4,4 '-BiPy and -BiPyH22+ on Au(111) electrode

We found using attenuated total reflection infrared (ATR-IR) spectroscopy t hat 4,4'-diprotonated bipyridine (BiPyH22+) adsorbs at the second layer out side the sulfate ions on a Au(1 1 1) surface at pH < 2.65 above ca. 0.0 V ( vs. Ag/AgCl). Based on the IR spectral change, the surface coverage of BiPy H22+ increases from -0.3 to -0.1 V at pH x 2.65 close to pK(al) of BiPyH22, while the BiPy coverage increases to +1.10 V as in the neutral Na(2)SaO(4 ) solution (pH = 7.1). The same BiPy adspecies were observed in 0.1 M HClO4 solution. Noteworthy is that BiPyH22+ adsorbs at the first layer and ClO4- at the second layer in this case. Furthermore, the surface coverage of BiP yH22+ and ClO4- increases up to ca. +0.8 V in Cl- containing solution, beca use the chemisorbed Cl- at the first layer stabilizes the BiPyH22+ and ClO4 - adsorption at the second and third layer, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.