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Revisiting the electronic structure of phosphazenes
Adrian B Chaplin1, John A Harrison, Paul J Dyson
1Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland. adrian.chaplin@epfl.ch
Inorganic Chemistry
|November 8, 2005
Summary
Ionic bonding dominates phosphazene electronic structure, with negative hyperconjugation contributing to a full description. This ionic model explains bond length alternation in polyphosphazenes, superseding older theories.
Area of Science:
- Inorganic Chemistry
- Computational Chemistry
- Quantum Chemistry
Background:
- Phosphazenes exhibit unique electronic structures with debated bonding models.
- Understanding substituent effects on phosphazene bonds is crucial for predicting material properties.
Purpose of the Study:
- Investigate the electronic structure of various phosphazene compounds.
- Critically evaluate proposed bonding models, including ionic and negative hyperconjugation.
- Explain the phenomenon of bond length alternation in polyphosphazenes.
Main Methods:
- Natural Bond Orbital (NBO) analysis to probe electronic structure.
- Topological electron density analysis to determine bonding features.
- Calculation of aromaticity indicators like NICS and PDI for cyclophosphazenes.
Main Results:
- Ionic bonding identified as the dominant feature in phosphazene electronic structure.
- Negative hyperconjugation contributes to a comprehensive bonding description.
- A combined ionic and negative hyperconjugation model successfully rationalizes bond length alternation, replacing d-orbital participation theories.
Conclusions:
- The study provides a refined understanding of phosphazene bonding.
- The proposed model offers a superior explanation for observed structural variations.
- Aromaticity in cyclophosphazenes is quantitatively assessed.