The efficiency of 2-amino-5-mercapto-1,3,4-thiadiazole and 2-methyl-5-mercapto-1,3,4-thiadiazole as copper corrosion inhibitors in neutral chloride environments was investigated. The study was carried out by means of a density-functional quantum-chemical approach and by impedance spectroscopy. The theoretical method was used to obtain a microscopic information about the surface-molecule interactions including the adsorption geometry conformations. Based on this information a physical model of the investigated system was proposed. A characteristic feature of it is the presence of interfacial phases between the bulk metal and the oxide and between the bulk oxide and the electrolyte. The derived model was relayed to an equivalent circuit which included the whole metal-oxide electrolyte system and the impedance data were fitted to it. The obtained estimates of the total dc path resistance showed that the studied thiadiazole derivatives were excellent copper corrosion inhibitors. (C) 2004 Elsevier Ltd. All rights reserved.