Ion-Pair Speciation in Aqueous Alkali Fluorides from Nuclear Magnetic Resonance of 19F

Published

April 9, 2026

Author(s)

Malgorzata Musial, Samantha Miller, Christopher Suiter, Heidi Klem, Eugene Paulechka, Kathleen Schwarz, Jason Widegren, Demian Riccardi

Abstract

We demonstrate that a combination of multiscale modeling and experimental 19F NMR can be used to examine the molecular details of how ion-pair speciation changes with temperature and molality. Excellent agreement with experimental 19F NMR chemical shifts is attained through the pairing of the theoretical ion-pair chemical shift profile with speciation populations estimated with molecular dynamics simulations and thermodynamic equilibrium constants. Clear periodic trends down Group I metal cations show that the ion-pair chemical shift profile is dominated by the shielding effects of pairing-induced dehydration for smaller cations (Li+ and Na+) that are overwhelmed by short-range deshielding effects for heavier cations (K+, Rb+, and Cs+). The experimental 19F NMR chemical shift trends with increasing temperature and molality are connected explicitly to changes in ion-pair populations relative to the free-ion state. This work provides a general approach to model ion pairing and solvation within the framework of NMR, which has implications for understanding ion-pairing phenomena in various systems.

Citation

Journal of American Chemical Society

Pub Type

Journals

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Keywords

19F NMR, Ion pairing, Ion solvation, Ion-pair speciation, Periodic trends, Multiscale modeling

Citation

Musial, M. , Miller, S. , Suiter, C. , Klem, H. , Paulechka, E. , Schwarz, K. , Widegren, J. and Riccardi, D. (2026), Ion-Pair Speciation in Aqueous Alkali Fluorides from Nuclear Magnetic Resonance of ¹⁹F, Journal of American Chemical Society, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=960603 (Accessed April 10, 2026)