Intermolecular charge-transfer complex between solute and ionic liquid: experimental and theoretical studies

Ground-state intermolecular donor-acceptor complex ([MCP][NTf2]-MN; 1:1) is formed between pi-electron of 1-methyl-naphthalene (MN) as solute (electron-rich) and pi+ electron of 1-methyl-4-cyanopyridinium bis((trifluoromethyl)sulfonyl)amide ([MCP][NTf2]) as solvent (electron deficient), observed in solid state. Intermolecular charge-transfer (IMCT) band is observed, indicating the formation of stable [MCP][NTf2]-MN complex. The IMCT process of [MCP][NTf2]-MN complex depends on relative strength of pi-pi+ stack between cation of [MCP][NTf2] IL and aromatic unit of MN. From DFT studies, it is clear that the geometry and interactions in [MCP][NTf2]-MN complex are also influenced by NTf2 anion. This solute-solvent interaction shows the deviation of inertness nature of [MCP][NTf2] IL. AIM analysis, electron localization function (ELF) and localized orbital locator (LOL) surface maps are obtained to achieve information regarding intermolecular interactions in the complex. Hirshfeld surface analysis and its fingerprint maps are used to identify pairwise interactions between atoms in order to avail molecular packing of the complexes from crystallographic data. NCI plots display combination of specific atom-atom interactions through hydrogen bond and vdW interactions. AIMD study shows that the complex attains a lower energy of - 2630.72 hartree at 125 and 445 fs.