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High-electron-density C6H6 units: stable ten-pi-electron benzene complexes.
Martin Diefenbach1, Helmut Schwarz
1Institute of Chemistry, Technical University Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.martin.diefenbach@mail.chem.tu-berlin.de
Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 19, 2005
Summary
Researchers predict the first stable benzene molecule with ten pi electrons. This aromatic stability is achieved in a bis(barium)benzene complex, where barium atoms donate electrons to the benzene ring.
Area of Science:
- Inorganic Chemistry
- Theoretical Chemistry
- Materials Science
Background:
- Aromaticity is a key concept in chemistry, typically associated with cyclic, planar molecules with delocalized pi electrons.
- Achieving aromaticity in systems with unusual electron counts or geometries presents a significant challenge.
Purpose of the Study:
- To computationally predict and characterize a novel stable benzene molecule with ten pi electrons.
- To investigate the role of barium as an electron-donating matrix in stabilizing such a complex.
Main Methods:
- Density Functional Theory (DFT) using the mPW1PW91 hybrid functional.
- Ab initio calculations employing the coupled-cluster expansion CCSD(T).
- Analysis of Nucleus Independent Chemical Shift (NICS) indices to confirm aromaticity.
Main Results:
- Prediction of the first stable benzene molecule featuring ten pi electrons.
- The bis(barium)benzene complex ([Ba2(C6H6)]) exhibits a D6h-symmetric structure with a 1A(1g) electronic ground state.
- Barium atoms act as an electron-donating matrix, stabilizing the aromatic benzene ring with four excess pi electrons.
Conclusions:
- The bis(barium)benzene complex represents a thermochemically stable, aromatic system with an unusual ten-pi-electron configuration.
- This work expands the understanding of aromaticity and electronic stabilization in organometallic compounds.
- Potential applications in molecular wires are suggested, utilizing similar sandwich structures.