Counting cations involved in cationic clusters of hydroxy-functionalized ionic liquids by means of infrared and solid-state NMR spectroscopy

Anne Strate, Jan Neumann, Thomas Niemann, Peter Stange, Alexander E. Khudozhitkov, Alexander G. Stepanov, Dietmar Paschek, Daniil I. Kolokolov, Ralf Ludwig

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

In hydroxy-functionalized ionic liquids, two types of hydrogen bonding coexist: the conventional H-bonds between cation and anion (c-a) and those between cation and cation (c-c), although the interaction between like-charged ions is supposed to be much weaker due to the repulsive Coulomb forces. Counting the cations involved in either (c-a) or (c-c) clusters is a challenge. For that purpose, we recently performed neutron diffraction (ND) measurements and molecular dynamics (MD) simulations at and above room temperature accompanied by NMR solid-state experiments in the glassy state of the ILs. In principle, these methods are suitable for determining the populations of (c-a) and (c-c) cluster species. For different reasons we could only address single temperatures and/or small temperature intervals above 300 K. The by far largest temperature range with reasonable efforts is accessible by simple infrared (IR) spectroscopy. However, counting (c-a) or (c-c) hydrogen bonds is a difficult task due to the different transition dipole moments resulting in varying intensities and broad vibrational bands. Here we present a method for deriving the number of cations involved in (c-a) ion pairs from IR spectra in the OH stretch region. This procedure provides access to the equilibria of (c-a) and (c-c) hydrogen bonds as a function of temperature allowing derivation of the transition enthalpy.

Original languageEnglish
Pages (from-to)6861-6867
Number of pages7
JournalPhysical chemistry chemical physics : PCCP
Volume22
Issue number13
DOIs
Publication statusPublished - 7 Apr 2020

Keywords

  • QUADRUPOLE COUPLING-CONSTANTS
  • INTERACTION STRENGTH
  • INTERACTION ENERGIES
  • CHARGE ATTRACTION
  • DISPERSION FORCES
  • DYNAMICS
  • BALANCE

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