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Spin-paired solvated electron couples in alkali-ammonia systems
Michael Mauksch1, Svetlana B Tsogoeva
1Department of Chemistry and Pharmacy, Institute of Theoretical Chemistry, Computer Chemistry Center, Nägelsbachstrasse 25a, 91052 Erlangen, Germany. michael.mauksch@fau.de.
Physical Chemistry Chemical Physics : PCCP
|November 6, 2018
Summary
Concentrated alkali metal solutions in ammonia exhibit diamagnetism due to spin-paired electron couples occupying solvent cavities. This pairing also explains the slow hydrogen evolution reaction from these unique solutions.
Area of Science:
- Physical Chemistry
- Computational Chemistry
Background:
- Alkali metals in liquid ammonia form deep blue solutions containing solvated electrons.
- Diamagnetism in more concentrated solutions requires explanation beyond single solvated electrons.
Purpose of the Study:
- To elucidate the nature of diamagnetism in concentrated alkali metal-ammonia solutions.
- To rationalize the observed sluggish hydrogen evolution kinetics.
Main Methods:
- Density Functional Theory (DFT) computations.
- Ab initio electronic structure calculations.
Main Results:
- Spin-paired electron couples can overcome Coulombic repulsion.
- These electron pairs occupy solvent cavities similar in size to single solvated electrons.
- A high activation barrier for the reaction between electron pairs and ammonia molecules was identified.
Conclusions:
- The diamagnetism of concentrated alkali metal-ammonia solutions is attributed to spin-paired electron couples in solvent cavities.
- The sluggish hydrogen evolution is a consequence of the high activation barrier for the electron pair's reaction with ammonia.
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