Interaction geometry in hexafluoroisopropyl alcohol-anion complexes: Differential solvent-dependent responses of...

Structure formation based on intermolecular interactions is often governed by primary hydrogen bonding; however, how interaction geometries are modulated by the environment remains insufficiently understood. Here, solvent-dependent interaction geometries in hexafluoroisopropyl alcohol (HFIP)-triflate (TfO^-) complexes were investigated using density functional theory (DFT). In the gas phase, all initial configurations converged to a short, nearly linear O-H···O hydrogen-bond anchor with well-defined secondary C-H···O interactions. In toluene, the anchor was largely preserved, whereas secondary interactions showed increased distances and pronounced geometric fluctuations. In DMSO, the anchor remained geometrically identifiable with only modest geometric changes, whereas secondary interactions became significantly elongated and effectively absent. Quantitative analysis revealed that the O-H···O distance changed only slightly across different solvent environments, whereas the secondary interaction distances increased markedly from the gas phase to DMSO. These results indicate that the primary O-H···O hydrogen-bond anchor is relatively retained across the solvent conditions examined, whereas the secondary C-H···O interactions exhibit substantially greater solvent-dependent geometric variations. Furthermore, this study extends previous findings on acidity-dependent interaction geometries to solvent environments, demonstrating that the interaction geometry framework can also describe solvent-dependent structural variations in the present model system.