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)(5)CH2CH(CH3)CO2H, CF3(CF2)(5)(CH2)(4)(CF2)(5)CF3 and {CF3(CF2)(5)CH2CH2}(3)P=O have been compared and a number of C-F center dot center dot center dot F-C and C-F center dot center dot center dot 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 center dot center dot center dot 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).