The potential-dependent behaviors of benzotriazole (BTAH) and 1-(methoxymethyl)-1H-benzotriazole (MeOMe-BTA) on copper surfaces were studied by cyclic voltammetry and in situ polarization modulation infrared reflection absorption spectroscopy. The identity of the anion in the supporting electrolyte has a significant effect on the formation and decomposition of the Cu(I)BTA multilayer surface complex. In chloride-containing solution, the Cu(I)BTA film is more easily formed. This film can be completely reduced upon excursion to more negative potentials. In sulfuric acid solution, the Cu(I)BTA film is formed less readily at more positive potentials and cannot be completely reduced at more negative potentials. The differences in the film formation/decomposition in the two electrolytes are attributed to coordination of the anion (Cl- or HSO4-) to the Cu(I) center of the Cu(I)BTA complex. Secondary ion mass spectrometric results also show that the anion coordination changes the amount of specific elements incorporated into the copper electrodeposit. MeOMe-BTA does not form a complex with copper due to blockage of one of the triazole ring nitrogens, and its electrochemical behavior is not affected by the anion identity.