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Expanded View of NMR Spin–Lattice Relaxation in Fluorine-Containing Ionic Liquids

Journal Article · · The Journal of Physical Chemistry Letters
 [1];  [2];  [1];  [1];  [3];  [4];  [1]
  1. City Univ. of New York (CUNY), NY (United States). Hunter College
  2. Department of Chemistry; New York City College of Technology
  3. University of Notre Dame, IN (United States)
  4. CeFEMA and Department of Physics; Instituto Superior Técnico, Universidade de Lisboa
+ Show Author Affiliations

Fluorine-containing anions are widely used in ionic liquids due to their unique physicochemical properties. However, the local dynamics of both cations and anions and their associated relaxation mechanisms remain incompletely understood. Here, we present a 1H and 19F spin–lattice relaxation rate (R1) study as a function of frequency over a broad frequency range from 30 kHz to 800 MHz for ionic liquids containing BF4–, PF6–, TFSI–, and FSI– anions and EMIM+ cation. By combining experimental R1H and R1F NMR dispersion (NMRD) profiles with relaxation models for both dipolar spin interactions and chemical shift anisotropy (CSA) contributions, we demonstrate that CSA is needed to accurately describe the R1F relaxation behavior above ∼300 MHz, the extent of which depends on the anion structure. These findings challenge the long-standing assumption that dipolar contribution is the main source of 19F relaxation in these systems and highlight the importance of including CSA to accurately interpret 19F relaxation in ionic liquids, particularly at high frequencies. This work provides new insights into the molecular dynamics of fluorine-containing species.

Research Organization:
City Univ. of New York (CUNY), NY (United States). Hunter College; Univ. of Notre Dame, IN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); Fundacio para a Ciencia e a Tecnologia
Grant/Contract Number:
SC0019409
OSTI ID:
2575423
Journal Information:
The Journal of Physical Chemistry Letters, Journal Name: The Journal of Physical Chemistry Letters Journal Issue: 30 Vol. 16; ISSN 1948-7185
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

anions
magnetic properties
quantum mechanics
salts
solvents