A DFT exploration of the organization of thiols on Au(111): a route to self-assembled monolayer of magnetic molecules

Abstract

Nitronyl nitroxides with thiol groups, NitRs, provide exciting opportunities for investigating the properties of magnetic SAMs on gold surfaces. Here we have employed periodic/molecular DFT calculations to study the energetics, structure, bonding and magnetic exchange of SAMs of nitronyl nitroxide radical thiols on Au(111). Two structures 4-(methylthio)phenyl nitronyl nitroxide (NitR-A-SCH₃), A = phenyl, and 4-(methylthio)methyl phenyl nitronyl nitroxide (NitR-B-SCH₃), B = phenyl-CH₂, have been chosen. The radical species of type NitR-B-S• is found to be energetically favourable with the reconstructed 1 : 2 Au_ad/thiols ratio model being the most favored structure. The computed structures are consistent with the experimental data (STM, ToF-SIMS and EPR) reported earlier. The computed magnetic exchange interactions in the SAMs of nitronyl nitroxide radicals reveal a stronger than expected intramolecular coupling, revealing the non-innocent nature of the gold surface.