An Archetype of Hydrogen Bonding Observed in Cationic Dimers of Carboxy-Functionalized Ionic Liquids by Means of NMR Solid State Spectroscopy – Reminiscent of Salt Bridges, Peptides and DNA | Sciact - CRIS-system of Boreskov Institute of Catalysis

An Archetype of Hydrogen Bonding Observed in Cationic Dimers of Carboxy-Functionalized Ionic Liquids by Means of NMR Solid State Spectroscopy – Reminiscent of Salt Bridges, Peptides and DNA ArticleGenre_short.SHORT_COMMUNICATION

Journal

PCCP: Physical Chemistry Chemical Physics
ISSN: 1463-9076 , E-ISSN: 1463-9084

Output data

Year: 2025, Volume: 27, Number: 12, Pages: 5949–5955 Pages count : 7 DOI: 10.1039/d5cp00303b

Tags

QUADRUPOLE COUPLING-CONSTANTS; CORRELATION TIMES; CHARGED IONS; RESONANCE; COMPLEXES; DEUTERON; STABILITY; CLUSTERS; ACID

Authors

Khudozhitkov Alexander E. ^1,5 , Hunger Lasse ² , Al-Sheakh Loai ² , Stepanov Alexander G. ¹ , Kolokolov Daniil I. ^1,5 , Ludwig Ralf ^2,3,4

Affiliations

1	Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk, 630090, Russia
2	Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, Dr-Lorenz-Weg 2, Rostock 18059, Germany
3	Department LL&M, University of Rostock, Albert-Einstein-Str. 25, Rostock 18059, Germany
4	Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert-Einstein-Str. 29a, Rostock 18059, Germany
5	Novosibirsk State University, Pirogova Street 2, Novosibirsk, 630090, Russia

Funding (3)

1	Russian Science Foundation	24-13-00129
2	German Research Foundation	LU 506/17-1 (Project 470038970)
3	German Research Foundation	LU-506/18-1 (Project 517661181)

Ion pair formation is a fundamental concept in chemistry. The association between ions of opposite charge is widely used in synthesis and catalysis. In contrast, there is little evidence for the formation of cationic or anionic dimers in solution. We report the strength and distribution of doubly hydrogen bonded cationic dimers (c+[double bond, length as m-dash]c+) in carboxy-functionalized ionic liquids [HOOC-(CH2)n-py][NTf2] with n = 2, 4, 5, 6, 7, and 9, probed by NMR solid-state spectroscopy. The two OH⋯O[double bond, length as m-dash]C H-bonds of the cationic dimers resemble the archetype H-bond motif known for formic acid. Herein, we clarify how the propensity for the formation of (c+[double bond, length as m-dash]c+) H-bonds depends on the alkyl chain length between the pyridinium ring and the carboxy group of the cations. For n = 9, the H-bond population is primarily dominated by cationic dimers (c+[double bond, length as m-dash]c+). Obviously, cooperative H-bond attraction is not only able to compensate for the repulsive Coulomb forces but also to ignore the H-bond accepting capabilities of the counter anion completely. In this regard, we provide the first evidence for quasi-isolated cationic dimers in solution that are stabilized by strong and directional (c+[double bond, length as m-dash]c+) H-bonds being as strong as the (m[double bond, length as m-dash]m) H-bonds between molecular mimics of the IL cations.

Khudozhitkov A.E. , Hunger L. , Al-Sheakh L. , Stepanov A.G. , Kolokolov D.I. , Ludwig R.
An Archetype of Hydrogen Bonding Observed in Cationic Dimers of Carboxy-Functionalized Ionic Liquids by Means of NMR Solid State Spectroscopy – Reminiscent of Salt Bridges, Peptides and DNA
PCCP: Physical Chemistry Chemical Physics. 2025. V.27. N12. P.5949–5955. DOI: 10.1039/d5cp00303b WOS Scopus ANCAN PMID

Submitted:	Jan 22, 2025
Accepted:	Feb 23, 2025
Published online:	Feb 24, 2025
Published print:	Mar 28, 2025

Web of science:	WOS:001436839100001
Scopus:	2-s2.0-85219582809
Chemical Abstracts:	2025:538715
Chemical Abstracts (print):	190:146373
PMID:	40040365

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