## 1 Introduction  
Due to its good thermal and electrical properties as well as resistance toward the influence of various chemical agents, copper has a wide range of industrial applications, electronics being one of them. Despite being quite a stable metal, copper is susceptible to dissolution or corrosion in aggressive aerated media, for instance, containing strong oxidants and acids. A protective passive layer is not formed in such media, which is why corrosion inhibitors should be used to prevent copper corrosion. Numerous studies of the possible inhibitors conducted to date have demonstrated that the most effective ones are organic compounds [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11] acting as complex agents and adsorbates on the copper metal surface. Introducing heteroatoms such as nitrogen, sulphur, and oxygen with free electron pairs as well as multiple conjugated chemical bonds and aromatic rings containing delocalised \(\pi\)-electrons into the structure of an organic molecule can substantially improve its inhibiting effect. This is accounted for by the fact that vacant d-orbitals in the atoms of copper can form coordinative bonds with heteroatoms and groups able to donate electrons, which results in effective chemisorption on the metal surface. Nitrogen-containing azoles, e.g., benzotriazole [12; 13] and benzimidazole [14], are the most common organic compounds that serve as inhibitors of copper corrosion in various media [15]. They get adsorbed on the copper surface and form a chemisorbed protective film. Sulphur-containing azole derivatives are excellent copper corrosion inhibitors in acidic media [16; 17; 18]. Taking into account the fact that the inhibition efficiency follows the sequence O \(<\) N \(<\) S [19], simultaneous introduction of a larger number of heteroatoms and groups into azole molecules is expected to yield a higher inhibition efficiency. This has been confirmed by a number of theoretical and experimental studies in the field of inhibition of copper corrosion by sulphur-containing compounds. Quantum-chemical calculations showed [20] that 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 is higher than that of benzotriazole. Heterocyclic compounds containing several different functional groups, e.g., OH, N=N, C=O, were observed to form Cu(II)-complexes [21] determining the protection properties of these organic molecules. 2-Amino-5-ethylthio-1,3,4-thiadiazole lowers the Cu corrosion rate greatly due to its strong adsorption onto the copper surface [22]. The strong adsorption of 1,3,4-thiadiazole [1], 1,2,4-triazole-3-thiole [4], and various mercapto-derivatives of tetrazole molecules on copper prevents the formation of soluble Cu chloride and oxychloride complexes in aerated chloride solutions, with the value of the inhibition efficiency being up to 100%. The introduction of an aromatic ring into mercapto-derivatives of 1,2,3,4-tetrazole and the possibility of simultaneous formation of several bridges of Cu(I) ions with N and S atoms results in a higher corrosion resistance of Cu in 0.1 M HNO\({}_{3}\)[7] and 1 mM H\({}_{2}\)SO\({}_{4}\)[8] solutions. The efficiency of copper corrosion inhibition in hydrochloric acid increases in the row 3-amino-1,2,4-triazole \(<\) 3-amino-mercapto-1,2,4-triazole \(<\) 3-amino-5-methylthio-1,2,4-triazole [10], i.e., when an S-atom is introduced into the azide molecule, and its molecular weight increases. It was shown [23] that the hydrophilic mercapto-group in the substituted benzenethiol molecules has a high affinity for copper and the inhibitor molecules anchor on the Cu surface via the thiolate bond, while the hydrophobic benzene ring with different substituents constitutes the ultra-thin protective monolayer.