The application of 4,5-dinitrobenzimidazole C7H3N(NH)(NO2)(2) (4,5-DNBIA) as a copper corrosion inhibitor in both mild acidic and alkaline phosphate solutions is reported. Electrochemical and spectroscopic studies reveal that copper exposed to solutions containing DNBIA results in the fast formation of Cu-(I)-DNBIA complex, with a film thickness of 2-5 nm. The thickness and the composition of the protective film depend on the solution's pH and applied potentials. The first step in the protective layer formation involves DNBIA's chemisorption by imidazole nitrogen followed by Cu(DNBIA)(2) complex coverage. Rapid protective film formation may be an advantage in applications where fast passivation is needed.