Probing Orientation-Specific Charge-Dipole Interactions between Hexafluoroisopropanol and Halides: A Joint Photoelectron Spectroscopy and Theoretical Study.

The interactions between hexafluoroisopropanol (HFIP) and halogen anions X- (F-, Cl-, Br-, and I-) have been investigated using negative ion photoelectron (NIPE) spectroscopy and ab initio calculations. The measured NIPE spectrum of each [HFIP·X]- (X = Cl, Br, and I) complex shows a pattern identical to the corresponding X- by shifting to the high electron binding energy side, indicative of the formation of the [HFIP···X-] structure in which X- interacts with HFIP via charge-dipole interactions. However, the spectrum of [HFIP·F]- appears completely different from that of F- and is more similar to the spectrum of the deprotonated HFIP anion (HFIP-H-). The geometry and electron density calculations indicate that a neutral HF molecule is formed upon HFIP interacting with F- via proton transfer, rendering a stable structure of [HFIP-H···HF]-. Two conformers of [HFIP-H·HF]- with HFIP being in synperiplanar and antiperiplanar configurations, respectively, are observed, providing direct experimental evidences to show the distinctly different and orientation-specific interactions between HFIP and halide anions.