Do TFSA Anions Slither? Pressure Exposes the Role of TFSA Conformational Exchange in Self-Diffusion.
Multinuclear ((1)H, (2)H, and (19)F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent (2)H T1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, as shown by their respective activation volumes (28.8 ± 2.5 cm(3)/mol for TFSA vs 14.6 ± 1.3 cm(3)/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV(‡)) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis. In addition, (2)H T1 data suggest increased ordering with increasing pressure, with two T1 regimes observed for the MD3 and D2 isotopologues between 0.1-100 and 100-250 MPa, respectively. The activation volumes for T1 were 21 and 25 cm(3)/mol (0-100 MPa) and 11 and 12 cm(3)/mol (100-250 MPa) for the MD3 and D2 isotopologues, respectively.
Physics Department, Brooklyn College , Brooklyn, New York 11210, United States.
Sophia N
SN
Suarez
Department of Physics, Hunter College , New York, New York 10021, United States.|CUNY Graduate School, New York, New York 10016, United States.
Armando
A
Rúa
Physics Department, Brooklyn College , Brooklyn, New York 11210, United States.|CUNY Graduate School, New York, New York 10016, United States.
David
D
Cuffari
Department of Physics, Hunter College , New York, New York 10021, United States.|CUNY Graduate School, New York, New York 10016, United States.
Kartik
K
Pilar
CUNY Graduate School, New York, New York 10016, United States.|Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
Jasmine L
JL
Hatcher
Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
Sharon
S
Ramati
Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
James F
JF
Wishart
D000838:Anions; D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008968:Molecular Conformation
D000838:Anions