TY - JOUR

T1 - Ion Mobility in Hydroxy-Functionalized Ionic Liquids Depends on Cationic Clustering: Tracking the Alkyl Chain Length Behavior with Deuteron NMR Relaxation

AU - Khudozhitkov, Alexander E

AU - Stepanov, Alexander G

AU - Kolokolov, Daniil I

AU - Ludwig, Ralf

PY - 2023/11/2

Y1 - 2023/11/2

N2 - Observing and quantifying the like-charge attraction in liquids and solutions is still challenging. However, we showed that elusive cation-cation hydrogen bonding may govern the structure and interaction in hydroxyl-functionalized ionic liquids. Therefore, cationic cluster formation depends on the shape, charge distribution, and functionality of the ions. We demonstrated by means of solid-state 2H NMR spectroscopy that cationic clusters change the structure and dynamics of ionic liquids. With increasing alkyl chain length, we observed two deuteron quadrupole coupling constants for the OD groups, differing by about 30 kHz. The lower value was assigned to the cation-cation interaction, indicating that the average (c-c) hydrogen bonds are stronger than the (c-a) hydrogen bonds between the cation and the anion despite the repulsive and attractive Coulomb interaction in the first and latter cases. Ion mobility could be studied by 2H NMR spectroscopy, although the deuterons in the hydrogen-bonded clusters underwent fast exchange. Our results also showed that simple relaxation models are not applicable anymore and that anisotropic motion must be considered.

AB - Observing and quantifying the like-charge attraction in liquids and solutions is still challenging. However, we showed that elusive cation-cation hydrogen bonding may govern the structure and interaction in hydroxyl-functionalized ionic liquids. Therefore, cationic cluster formation depends on the shape, charge distribution, and functionality of the ions. We demonstrated by means of solid-state 2H NMR spectroscopy that cationic clusters change the structure and dynamics of ionic liquids. With increasing alkyl chain length, we observed two deuteron quadrupole coupling constants for the OD groups, differing by about 30 kHz. The lower value was assigned to the cation-cation interaction, indicating that the average (c-c) hydrogen bonds are stronger than the (c-a) hydrogen bonds between the cation and the anion despite the repulsive and attractive Coulomb interaction in the first and latter cases. Ion mobility could be studied by 2H NMR spectroscopy, although the deuterons in the hydrogen-bonded clusters underwent fast exchange. Our results also showed that simple relaxation models are not applicable anymore and that anisotropic motion must be considered.

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85175878316&origin=inward&txGid=02879fe00745af6a9b91d664c609c480

U2 - 10.1021/acs.jpcb.3c05330

DO - 10.1021/acs.jpcb.3c05330

M3 - Article

C2 - 37857325

VL - 127

SP - 9336

EP - 9345

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 43

ER -