DFT studies of 2-mercaptobenzothiazole and 2-mercaptobenzimidazole as corrosion inhibitors for copper

Abstract

This work describes 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI) adsorption on Cu(111) by a systematic DFT study. Whatever the surface coverage of the adsorbed molecule, the adsorption is favored when the exocyclic sulfur atom is unprotonated (i.e. thione and thiolate forms). At low molecular density, the molecules adsorb forming a Cu-S(exo) and a Cu-N bond, and the adsorption energies of both molecules are similar, around 1.2 eV. To investigate a coverage corresponding to the density of self-assembled films, two strategies were applied: on the one hand, the best epitaxial relationship between the molecular layer and the Cu(111) surface was searched. A reasonable accommodation was found for a molecular density of 3.9 molecule/nm² in the honeycomb (3 × 3) Cu(111) superstructure, in which the molecules are adsorbed with the C2v axis tilted, forming two Cu-S bonds for MBT and one Cu-S and one Cu-N bond for MBI. On the other hand, the best structure for atomic S on Cu(111), the (√7 x √7) R19° superstructure, with a molecular coverage of 5 molecule/nm2, was considered. We find that the honeycomb MBT and MBI layer is the most stable arrangement, showing that in this case, the molecular organization prevails over the head-group/surface interaction. The MBI molecule adsorbs more strongly than the MBT molecule, due to better lateral interactions in the organic layer.