Intramolecular pi-pi Interactions in Flexibly Linked Partially Fluorinated Bisarenes in the Gas Phase

摘要

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2)(3) and (CH2)(2)SiMe2 units were synthesized by hydrosilylation and C-C coupling reactions. Their solid-state structures are dominated by intermolecular stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular pi-pi interactions. For the silicon compounds, structures characterized by sigma-pi interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6H5(CH2)(3)C6F5, in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations.