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One-Dimensional Ionic Self-Assembly in a Fluorous Solution: The Structure of Tetra-n-butylammonium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate in Perfluoromethylcyclohexane by Small-Angle Neutron Scattering (SANS)

Published

Author(s)

Kenneth A. Rubinson, Philippe Buhlmann, Thomas C. Allison

Abstract

Fluorous liquids are the least polarizable condensed phases known, and their nonpolar members form solutions with conditions the closest to being in vacuo. A soluble salt consisting of a large fluoroborate anion, tetrakis[3,5-bis(perfluorohexyl)phenyl]borate, and its counterion, tetra-n-butylammonium, dissolved in perfluoromethylcyclohexane produces ionic solution with extremely low conductivity. These solutions were subjected to small-angle neutron scattering (SANS) to ascertain the solute structure. At concentration of 9% weight fraction, the fluorophilic electrolyte forms straight, long (>200 A) self-assembled structures that are, in essence, long, homogeneous cylinders. Molecular models were made assuming a requirement for electroneutrality on the shortest length scale possible. This shows a structure formed from a stack of alternating anions and cations, and the structures fir the experimental scattering well. At the lower concentration of 1%, the stacks of ion pairs are shorter and eventually break up to form solitary ion pairs in the solution. These characteristics suggest such conditions provide an interesting new way to form long, self-assembling ionic nanostructures with single-molecule diameters in free solution onto which various moieties could be attached.
Citation
Physical Chemistry Chemical Physics
Volume
18
Issue
14

Keywords

SANS, non-conducting ionic solution, perfluorocarbon solvent, fluorous

Citation

Rubinson, K. , Buhlmann, P. and Allison, T. (2016), One-Dimensional Ionic Self-Assembly in a Fluorous Solution: The Structure of Tetra-n-butylammonium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate in Perfluoromethylcyclohexane by Small-Angle Neutron Scattering (SANS), Physical Chemistry Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=920001 (Accessed September 17, 2021)
Created April 14, 2016, Updated February 19, 2017