Die zweigesichtige Natur der Wasserstoffbrückenbindung in hydroxylfunktionalisierten ionischen Flüssigkeiten, offenbart durch Neutronendiffraktometrie und Molekulardynamik‐Simulation

Niemann, Thomas; Neumann, Jan; Stange, Peter; Gärtner, Sabrina; Youngs, Tristan G. A.; Paschek, Dietmar; Warr, Gregory G.; Ludwig, Ralf

doi:10.1002/ange.201904712

Angewandte Chemie

2019

DOI: 10.1002/ange.201904712

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Die zweigesichtige Natur der Wasserstoffbrückenbindung in hydroxylfunktionalisierten ionischen Flüssigkeiten, offenbart durch Neutronendiffraktometrie und Molekulardynamik‐Simulation

Thomas Niemann

Jan Neumann

Peter Stange

et al.

Abstract: Wir charakterisieren Wasserstoffbrückenbindungen in hydroxyfunktionalisierten ionischen Flüssigkeiten mittels Neutronendiffraktometrie isotopensubstituierter Proben (NDIS), Molekulardynamik-Simulationen (MD) und quan-tenchemischenB erechnungen. NDIS-Daten werden mithilfe der "empirical potential structure refinement"-Technik (EPSR) angepasst, um die H···O-und O···O-Paarverteilungsfunktionen fürW asserstoffbrücken zwischen Ionen entgegengesetzter und gleicher Ladung zu ermitteln. Trotz der abstoßenden Coulomb-K… Show more

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Cited by 5 publications

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“…For all ILs the DQCCs for the (c-c) hydrogen bonds are between 40 and 60 kHz smaller than for the (c-a) species indicating stronger interaction. Such a difference is in accord with corresponding red-shifted OH vibrational bands and shortening of intermolecular O···O distances obtained from neutron diffraction measurements . However, decreasing DQCCs with increasing hydroxalkyl chains due to enhanced (c-c) cluster formation as observed in the liquid phase cannot be reported for temperatures below the glass transition.…”

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Freezing the Motion in Hydroxy-Functionalized Ionic Liquids–Temperature Dependent NMR Deuteron Quadrupole Coupling Constants for Two Types of Hydrogen Bonds Far below the Glass Transition

Khudozhitkov

Niemann

Stange

et al. 2020

J. Phys. Chem. Lett.

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We measured the deuteron quadrupole coupling constants (DQCCs) for hydroxy-functionalized ionic liquids (ILs) with varying alkyl chain length over the temperature range between 60 and 200 K by means of solid-state NMR spectroscopy. For all temperatures, the 2H spectra show two DQCCs representing different types of hydrogen bonds. Higher values, ranging from 220 to 250 kHz, indicate weaker hydrogen bonds between cation and anion (c-a), and lower values varying from 165 to 210 kHz result from stronger hydrogen bonds between the OD groups of cations (c-c), in agreement with recent observations in infrared, neutron diffraction, and NMR studies. We observed different temperature dependencies for (c-a) and (c-c) hydrogen bonding. From the static pattern of the 2H spectra at the lowest temperatures, we derived the true DQCCs being up to 20 kHz larger than recently reported values measured at the glass transition temperature. We were able to freeze the librational motions of the hydrogen bonds in the ILs. The temperature dependence of the (c-a) and (c-c) cluster populations in the glassy state is opposite to that observed in the liquid state, partly anticipating the behavior of ILs tending to crystallize.

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confidence: 99%

Freezing the Motion in Hydroxy-Functionalized Ionic Liquids–Temperature Dependent NMR Deuteron Quadrupole Coupling Constants for Two Types of Hydrogen Bonds Far below the Glass Transition

Khudozhitkov

Niemann

Stange

et al. 2020

J. Phys. Chem. Lett.

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Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems

et al. 2019

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We present deuteron quadrupole coupling constants (DQCC) for hydroxyl-functionalized ionic liquids (ILs) in the crystalline or glassy states characterizing two types of hydrogen bonding:T he regular Coulomb-enhanced hydrogen bonds between cation and anion (c-a), and the unusual hydrogen bonds between cation and cation (c-c), which are present despite repulsive Coulomb forces.W em easure these sensitive probes of hydrogen bonding by means of solid-state NMR spectroscopy. The DQCCs of (c-a) ion pairs and (c-c) Hbonds are compared to those of salt bridges in supramolecular complexes and those present in molecular liquids.A tl ow temperatures,t he (c-c) species successfully compete with the (c-a) ion pairs and dominate the cluster populations.Equilibrium constants obtained from molecular-dynamics (MD) simulations show vantH off behavior with small transition enthalpies between the differently H-bonded species.W eshow that cationic-cluster formation prevents these ILs from crystallizing.W ith cooling,t he (c-c) hydrogen bonds persist, resulting in supercooling and glass formation.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems

et al. 2019

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We present deuteron quadrupole coupling constants (DQCC) for hydroxyl‐functionalized ionic liquids (ILs) in the crystalline or glassy states characterizing two types of hydrogen bonding: The regular Coulomb‐enhanced hydrogen bonds between cation and anion (c–a), and the unusual hydrogen bonds between cation and cation (c–c), which are present despite repulsive Coulomb forces. We measure these sensitive probes of hydrogen bonding by means of solid‐state NMR spectroscopy. The DQCCs of (c–a) ion pairs and (c–c) H‐bonds are compared to those of salt bridges in supramolecular complexes and those present in molecular liquids. At low temperatures, the (c–c) species successfully compete with the (c–a) ion pairs and dominate the cluster populations. Equilibrium constants obtained from molecular‐dynamics (MD) simulations show van't Hoff behavior with small transition enthalpies between the differently H‐bonded species. We show that cationic‐cluster formation prevents these ILs from crystallizing. With cooling, the (c–c) hydrogen bonds persist, resulting in supercooling and glass formation.

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Die zweigesichtige Natur der Wasserstoffbrückenbindung in hydroxylfunktionalisierten ionischen Flüssigkeiten, offenbart durch Neutronendiffraktometrie und Molekulardynamik‐Simulation

Cited by 5 publications

References 62 publications

Freezing the Motion in Hydroxy-Functionalized Ionic Liquids–Temperature Dependent NMR Deuteron Quadrupole Coupling Constants for Two Types of Hydrogen Bonds Far below the Glass Transition

Freezing the Motion in Hydroxy-Functionalized Ionic Liquids–Temperature Dependent NMR Deuteron Quadrupole Coupling Constants for Two Types of Hydrogen Bonds Far below the Glass Transition

Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems

Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems

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