Combined studies on the surface coordination chemistry of benzotriazole at the copper electrode by direct electrochemical synthesis and surface-enhanced Raman spectroscopy

The surface coordination chemistry of benzotriazole (BTAH) on a Cu electrode was investigated by electrochemical synthesis of surface complexes and in situ electrochemical surface-enhanced Raman spectroscopy (SERS) in nonaqueous solution. Two different surface complexes were prepared in solution with or without triphenylphosphane (PPh3). A new mixed-valence Cu-N cluster compound containing BTAH was synthesized by direct electrochemical oxidation of Cu in nonaqueous solutions with PPh3. The final product, Cu5Cl(BTA)(5)(PPh3)(4) was crystallized and characterized by microanalysis and Raman spectroscopy together with X-ray crystallographic determinations. The complex crystallized in a monoclinic space group (P2(1)/n) with lattice parameters a 16.739(2) angstrom, b = 18.919(2) angstrom, c = 31.042(4) angstrom, ss=103.194(3)degrees, V = 9571.0(19) angstrom(3), R-1 = 0.0704, wR(2) = 0.1643. The results showed that the complex was a pentanuclear compound. The central Cu-II atom is coordinated to four equatorial and one axial BTA(-) ligands to form a distorted tetragonal pyramidal coordination polyhedron, whereas each surrounding Cu-I ion is in a distorted tetrahedral environment. The in situ SERS studies revealed that the BTA(-) ion was coordinated to a Cu surface through its two N atoms of the triazole ring to form a surface polymer complex of [Cu(BTA)](n), which suppressed the dissolution and oxidation of Cu effectively. The introduction of PPh3 blocked the surface coordination of BTAH with the electrode, and a complex of BTA(-) and PPh3 with Cu was formed in the bulk solution. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).