Fluorine–Fluorine Interactions in the Solid State: An Experimental and Theoretical Study

The solid state structures of three compounds that contain a perfluorinated chain, CF3(CF2)5CH2CH(CH3)CO2H, CF3(CF2)5(CH2)4(CF2)5CF3 and {CF3(CF2)5CH2CH2}3PO have been compared and a number of C–F···F–C and C–F···H–C interactions that are closer than the sum of the van der Waals radii have been identified. These interactions have been probed by a comprehensive computational chemistry investigation and the stabilizing energy between dimeric fragments was found to be 0.26–29.64 kcal/mol, depending on the type of interaction. An Atoms-in-Molecules (AIM) study has confirmed that specific C–F···F–C interactions are indeed present, and are not due simply to crystal packing. The weakly stabilizing nature of these interactions has been utilized in the physisorption of a selected number of compounds containing long chain perfluorinated ponytails onto a perfluorinated self-assembled monolayer, which has been characterized by IRRAS (Infrared Reflection Absorption Spectroscopy).