Effects of number, type and length of the alkyl-chain on the structure and property of indazole derivatives used as corrosion inhibitors

In this study, three series of new indazole derivatives linked with double long alkyl-chains (N-alkyl-chain, O-alkyl-chain or S-alkyl-chain) were designed. Then, to estimate the potential used as corrosion inhibitors and effects of number, type and length, their geometries, frontier molecular orbital energies, global electrophilicity index, nucleophilicity index, absolute electronegativity, absolute hardness, softness, a fraction of electrons transferred, Fukui functions and binding energy were investigated by the density functional theory method and molecular dynamics simulation. The results showed that the introduced second long chain has significant effects on the anti-corrosive properties and is very helpful for improving the inhibition efficiency. Among three long-chains, the N-alkyl-chain is favorable for donating electrons to metals, while the S-chain is good for accepting electrons to form feedback bonds. Both the N-alkyl-chain and O-alkyl-chains are much more convenient for forming big water-block than the S-alkyl chain. As a result, inhibitors linked with two N-alkyl-chains may have higher inhibition efficiency than others. When the length of the long-chain is longer than eight carbon atoms, most anti-corrosive properties will not change any more obvious, but the binding energy will decrease, and the adsorption strength between inhibitors and metals may be weakened because of the curling, bending and repulsion of long chains. The N3/O/S, N1, C1, C4, C6 and C7 atoms are possible reactive sites to donate electrons, while N2, C1, C4, C5, C7 and N1 atoms are the main electrophilic centers to form feedback bonds. This work may be helpful for developing new multi-chain organic corrosion inhibitors.