First crystalline salt of 1,1-bis-(carboxymethylthio)-1-phenylethane: synthesis, crystal structure, Hirshfeld surface analysis, and computational study

The reaction of 1,1-bis-(carboxymethylthio)-1-phenylethane with piperidine was conducted in an acetone solution at a molar ratio of the initial components of 1:2. As a result, a new compound was obtained: piperidinium-1,1-bis-(carboxymethylthio)-1-phenylethane, characterized by FT-IR. The crystal structure of the synthesized compound is structurally elucidated via single crystal XRD technique, indicating that a H-atom is transferred from half of the piperidinium-1,1-bis-(carboxymethylthio)-1-phenylethane part to the piperidine ring and the structure is a salt in nature. N–H⋯O and C–H⋯O bondings contribute to the stability and enforcement of crystal packing; further assessment is supported via Hirshfeld surface analysis, considering interatomic contacts. We employed density functional theory (DFT)-based computations along with molecular dynamics (MD) simulations in a systematic manner, aiming for the investigation of the stabilizing interactions and electronic characteristics of the molecular ionic compound. The structural framework is notably stabilized by dual N–H···O hydrogen bonding, originating from piperidine rings positioned on either side of the central fragment. Electronic structure analysis revealed intermolecular charge transfer characteristics through HOMO–LUMO orbital distributions, complemented by TD-DFT studies of excited state behavior. Furthermore, ab initio MD simulations at 300 K conclusively demonstrated the ionic compound's robust kinetic and dynamic stability.