TY - JOUR

T1 - Structure, hydrogen bond dynamics and phase transition in a model ionic liquid electrolyte

AU - Khudozhitkov, Alexander E.

AU - Stange, Peter

AU - Stepanov, Alexander G.

AU - Kolokolov, Daniil I.

AU - Ludwig, Ralf

N1 - Funding Information: This work has been supported by the Russian Science Foundation (grant no. 21-13-00047). R. L. is grateful to the Deutsche Forschungsgemeinschaft (DFG) for financing the projects LU 506/15-1 (grant no. 401427621). D. I. K. thanks the Alexander von Humboldt Foundation (AvH) for awarding a Humboldt Research Fellowship for Experienced Researchers. Publisher Copyright: This journal is © the Owner Societies

PY - 2022/2/11

Y1 - 2022/2/11

N2 - We show that solid-state NMR spectroscopy is a suitable method for characterizing the structure, hydrogen bond dynamics and phase transition behavior in protic ionic liquids (PILs). Deuteron line shape and spin relaxation time analysis provide a description of the structural and dynamical heterogeneity in the solid state of the model PIL triethyl ammonium bis(trifluoromethanesulfonyl)amide [TEA][NTf2]. Therein, we observed two deuteron quadrupole coupling constant for the ND bond of the TEA cation, indicating differently strong hydrogen bonds to the nitrogen and oxygen atoms of the NTf2 anion, as we could confirm by DFT calculations. The transition processes in the dynamically heterogeneous phase are characterized by two standard molar enthalpies and thus different stages of melting. We provide geometry, rates and energetics of the cation in the solid and liquid states of the PIL. Comparison with PILs having stronger interacting anions shows higher enthalpy change between the solid and liquid states, lower activation barriers of tumbling motion and higher amplitude of librational motion for the TEA cation in the presence of the weakly interacting anion NTf2. We provide reasonable relations between microscopic and macroscopic properties, as is relevant for any kind of application.

AB - We show that solid-state NMR spectroscopy is a suitable method for characterizing the structure, hydrogen bond dynamics and phase transition behavior in protic ionic liquids (PILs). Deuteron line shape and spin relaxation time analysis provide a description of the structural and dynamical heterogeneity in the solid state of the model PIL triethyl ammonium bis(trifluoromethanesulfonyl)amide [TEA][NTf2]. Therein, we observed two deuteron quadrupole coupling constant for the ND bond of the TEA cation, indicating differently strong hydrogen bonds to the nitrogen and oxygen atoms of the NTf2 anion, as we could confirm by DFT calculations. The transition processes in the dynamically heterogeneous phase are characterized by two standard molar enthalpies and thus different stages of melting. We provide geometry, rates and energetics of the cation in the solid and liquid states of the PIL. Comparison with PILs having stronger interacting anions shows higher enthalpy change between the solid and liquid states, lower activation barriers of tumbling motion and higher amplitude of librational motion for the TEA cation in the presence of the weakly interacting anion NTf2. We provide reasonable relations between microscopic and macroscopic properties, as is relevant for any kind of application.

UR - http://www.scopus.com/inward/record.url?scp=85126072285&partnerID=8YFLogxK

U2 - 10.1039/d2cp00452f

DO - 10.1039/d2cp00452f

M3 - Article

C2 - 35212342

AN - SCOPUS:85126072285

VL - 24

SP - 6064

EP - 6071

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 10

ER -