Coordinative Properties of Highly Fluorinated Solvents with Amino and Ether Groups

Abstract

In spite of the widespread use of perfluorinated solvents with amino and ether groups in a variety of application fields, the coordinative properties of these compounds are poorly known. It is generally assumed that the electron withdrawing perfluorinated moieties render these functional groups rather inert, but little is known quantitatively about the extent of their inertness. This paper reports on the interactions between inorganic monocations and perfluorotripentylamine and 2H-perfluoro-5,8,11-trimethyl-3,6,9,12-tetraoxapentadecane, as determined with fluorous liquid-membrane cationselective electrodes doped with tetrakis[3,5-bis(perfluorohexyl)phenyl]borate salts. The amine does not undergo measurable association with any ion tested, and its formal pK a is shown to be smaller than -0.5. This is consistent with the nearly planar structure of the amine at its nitrogen center, as obtained with density functional theory calculations. The tetraether interacts very weakly with Na + and Li + . Assuming 1:1 stoichiometry, formal association constants were determined to be 2.3 and 1.5 M -1 , respectively. This disproves an earlier proposition that the Lewis base character in such compounds may be non-existent. Due to the extremely low polarity of fluorous solvents and the resulting high extent of ion pair formation, a fluorophilic electrolyte salt with perfluoroalkyl substituents on both the cation and the anion had to be developed for these experiments. In its pure form, this first fluorophilic electrolyte salt is an ionic liquid with a glass transition temperature, T g , of -18.5 °C. Interestingly, the molar conductivity of solutions of this salt increases very steeply in the high concentration range, making it a particularly effective electrolyte salt.

Gels from a semifluorinated n-alkane in fluorinated solvents as a probe for intermolecular interactions

“…We remark here that also in PFTBA the dipole moment is practically negligible, as the electron attracting power of fluorine atoms forces the molecule to adopt a planar geometry (see the molecular model depicted in Fig. 3) instead of the typical pyramidal structure of regular amines, and the presence of the three perfluorobutyl chains results in a bulky branched structure [32].…”

“…Since to the best of our knowledge no experimental value for a and I of FCs was found in the literature, we calculated the polarizability according to Le and Weers [43], and the ionization potential was estimated according to Reed [44]. The dipole moment of PF6, PF7, PF8, PFD and PFTBA is zero [32,45]. While, due to the presence of the bromide atom in PFOB, and because of the CF 2 -CH 2 bond in F 8 H 16 , these two molecules possess a non-zero l [3,4].…”

Electroanalytical Sensor Technology

“…In each instance improved selectivity is reported coupled with favourable LODs. Buhlmann's group having reported the success of highly fluorinated liquid phases as sensing materials, detailing the design of numerous ion-selective sensors which incorporate fluorinated membranes [129][130][131].…”

Noncovalent associations in fluorous fluids

“…In 2005, Bü hlmann and coworkers reported the first quantitative data on the coordinative properties of perfluoroethers and perfluoralkylamines towards monocations [21]. They have shown that the selectivity (potentiometric measurement and referenced to Cs + ) of a fluorous-liquid membrane loaded with 14 for the small ions Na + and Li + was modified when using the perfluoroether 24 (Scheme 10) as the fluorous liquid phase instead of the perfluorodecalin or perfluoroperhydrophenanthrene.…”