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Updated: Jun 22, 2026
06:35
Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
Published on: February 15, 2016
Ion pairing and salt structure in organic salts through diffusion, Overhauser, DFT and X-ray methods
Aitor Moreno1, Paul S Pregosin, Luis F Veiros
1Laboratory of Inorganic Chemistry, ETHZ, Hönggerberg, 8093 Zürich, Switzerland.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|June 9, 2009
Summary
This study investigates ion pairing in brucinium salts and aryl carbocations using NMR spectroscopy. Solvent and cation structure influence anion positioning, revealing novel interactions and aggregation effects.
Area of Science:
- Physical Organic Chemistry
- Supramolecular Chemistry
- Spectroscopy
Background:
- Understanding ion pairing is crucial for predicting chemical reactivity and physical properties of ionic compounds.
- Brucinium salts and aryl carbocations represent diverse ionic structures with varying electronic and steric properties.
- Solvent effects significantly influence the behavior of ionic species in solution.
Purpose of the Study:
- To characterize the pulsed gradient spin-echo (PGSE) diffusion characteristics of novel brucinium salts and aryl carbocations.
- To investigate the influence of solvent polarity and cation structure on ion pairing interactions.
- To elucidate the spatial arrangement of anions relative to carbocations using NMR spectroscopy.
Main Methods:
- Pulsed gradient spin-echo (PGSE) diffusion measurements.
- Proton and Fluorine Nuclear Overhauser Effect Spectroscopy (1H, 19F HOESY NMR).
- Density Functional Theory (DFT) calculations.
- Solid-state X-ray crystallography.
- 195Pt NMR and field-dependent T1 measurements.
Main Results:
- Solvent dependence indicates strong ion pairing in CDCl3, intermediate in CD2Cl2, and weak in [D6]acetone.
- HOESY NMR reveals specific anion-cation interactions and positional variations of the BF4- anion in aryl carbocations.
- The anion's position relative to the carbocation is dependent on the carbocation's structure, a novel observation.
- Solid-state structures of a brucinium salt and a Zeise's salt derivative were determined.
- NMR and T1 measurements suggest similarities between the brucinium-based Zeise's salt and K[PtCl3(C2H4)], and are useful for detecting aggregation.
Conclusions:
- Ion pairing strength is significantly influenced by solvent polarity and the nature of both cation and anion.
- The study demonstrates a novel positional dependence of anions on carbocation structure, supported by DFT calculations.
- NMR techniques, including HOESY and T1 measurements, are powerful tools for characterizing ion pairing and aggregation in ionic systems.
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