Ion Aggregation and R3N+–C(R)–H···NR3 Hydrogen Bonding in a Fluorous Phase

Potentiometric selectivities show that in fluorous ion-selective electrode membranes the tetrabutylammonium ion binds to fluorophilic proton ionophores. For the ionophore bis­[3-(perfluorooctyl)­propyl]­(2,2,2-trifluoroethyl)­amine, this type of interaction is confirmed by the effect of the ionophore on the ionic conductivity of perfluoro­(perhydrophenanthrene) solutions of a fluorophilic NBu4 + salt. In this system, ion pairs, triple ions, and higher ionic aggregates dominate over single ions, and the ionophore increases the conductivity by favoring the formation of ion aggregates with a net charge. These observations are consistent with the formation of R3N+–C­(R)–H···NR3 type hydrogen bonds between the nitrogen atom of the ionophore and the hydrogen atoms in the α position to the positively charged quaternary ammonium center of NBu4 +. Similar interactions were observed in a number of crystalline phases. To date, observations of C–H···N type hydrogen bonds in liquid phases have been very few, and solution-phase N+–C–H···N type hydrogen bonds have not been reported previously. Interestingly, no interactions between NBu4 + and the more basic ionophore tridodecylamine were observed in conventional plasticized poly­(vinyl chloride) membranes doped with the ionophore tridodecylamine, emphasizing the uniquely low polarity of fluorous phases.