Flexible Acyclic Polyol-Chloride Anion Complexes and Their Characterization by Photoelectron Spectroscopy and
Alireza Shokri1, Xue-Bin Wang2, Yanping Wang3
1Department of Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States.
The Journal of Physical Chemistry. A
|February 25, 2016
Summary
Flexible alcohols binding to chloride anions were studied using photoelectron spectroscopy and computations. Larger polyols showed stronger hydrogen bonding, influencing detachment energies and binding constants, with complex entropic and enthalpic factors at play.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Spectroscopy
Background:
- Flexible acyclic alcohols with varying hydroxyl groups were investigated.
- Complexation with chloride anions was a key focus.
- Understanding hydrogen bonding in alcohol-anion systems is crucial.
Purpose of the Study:
- To investigate the electronic properties of alcohol-chloride anion complexes.
- To determine binding affinities and thermodynamic parameters in solution.
- To elucidate the role of hydrogen bonding networks in these interactions.
Main Methods:
- Negative ion photoelectron spectroscopy (NIPES) was employed.
- Density Functional Theory (DFT) computations (M06-2X/aug-cc-pVTZ) were used for theoretical analysis.
- Solution equilibrium binding constants were measured using tetrabutylammonium chloride (TBACl) in acetonitrile at various temperatures.
Main Results:
- Vertical detachment energies (VDEs) ranged from 4.45-5.96 eV, well-reproduced by DFT.
- Larger polyols exhibited significantly higher VDEs due to extensive hydrogen bonding.
- Solution binding constants showed similar free energies of association (ΔG° = -2.8 ± 0.7 kcal mol⁻¹) across different alcohols.
- Thermodynamic analysis revealed counterintuitive entropic favorability and enthalpic disfavorability for larger alcohols in solution.
Conclusions:
- Hydrogen bond networks in alcohol-Cl(-) complexes significantly impact electronic detachment energies.
- Ionic and nonionic hydrogen bonds are energetically comparable in larger polyols.
- Solution thermodynamics suggest increased solvent release upon binding larger alcohols, leading to negative heat capacities.
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