Raman spectroscopic studies on surface coordination mechanism of benzotriazole and triphenylphosphine with metals

The complexes of benzotriazole (BTAH) with Ag, Cu, Fe, Zn and Ni were prepared respectively in the non-aqueous solution by the direct electrochemical synthesis and characterized by microanalysis and normal Raman spectroscopy. The influence of the neutral ligand of triphenylphosphine (pph₃) on the coordination process was deduced by the normal Raman spectroscopy and electrochemistry. The metals were classified into two categories. For the first type, such as Cu and Ag, CuBTA and AgBTA were obtained in the solution without pph₃. The introduction of pph₃ led to its participation in the coordination processes of BTAH with Cu or Ag and appeared in the final complex. Fe, Zn and Ni belonged to the second type, there was no influence on the coordination of BTAH with Zn, Ni and Fe, i.e., the final complexes were Fe(BTA)₂, Zn(BTA)₂ and Ni(BTA)₂, respectively, in the solution with/without pph₃. The electrochemical results revealed that the BTAH can inhibit the corrosion of all the above metals, and the introduction of pph₃ resulted in the decrease of inhibition efficiency to Cu surface, while no influence was observed on the Ni surface. The different role of pph₃ was explained in terms of hard/soft acids and bases rule and coordination mechanism was proposed.