Interactions and mechanisms of sulfonium salts with metal interfaces: An in-depth computational exploration of COSMO-RS profiles, quantum chemistry and molecular dynamics on iron, copper, and aluminum

Sulfonium salts (SSs) exhibit diverse structural and electronic attributes, offering rich prospects in corrosion inhibition strategies. This research employed a combination of methodologies, such as COSMO-RS and Density Functional Theory (DFT), to investigate six specific SSs, including Phenacyl dimethyl sulfonium bromide (SH) and its p-derivatives 4-Methyl-SH (SM), 4-Chloro-SH (SC), 4-Bromo-SH (SB), 4-Methoxy-SH (SMe), and 4-NitroSH (SN). Additionally, Molecular Dynamics (MD) simulations were utilized to examine their adsorption configurations and affinities to Fe, Cu, and Al surfaces. The initial investigation through COSMO-RS sigma-profiles confirmed the SSs' propensity for hydrogen bonding in water. Quantum chemical calculations (QCCs) further elucidated the distinctive reactivity effects of various functional groups. For instance, methyl-substituted SS displayed remarkable reactivity with metals, whereas nitro groups led to strong electron acceptance in the SN molecule. Fukui functions identified pronounced electrophilic and nucleophilic characteristics within atoms, with carbonyl atoms emerging as key reactive sites. MD simulations provided insights into the adsorption of SSs on metal surfaces, revealing parallel disposition as the most stable mode and a strong affinity towards copper, iron, and aluminum, in the order of SM > SMe > SH > SB > SC > SN. This correlation aligned with the Delta N data. The study revealed the substantial effects of both methyl and methoxy groups on SSs' reactivity with metals, with electron-withdrawing groups exerting a negative influence. Overall, the findings enrich our comprehension of SSs and offer a solid foundation for their further exploration and utilization, especially in customized design and applications such as corrosion protection.