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Chemical bonding in hypervalent molecules: is the octet rule relevant?
Stéphane Noury1, Bernard Silvi, Ronald J Gillespie
1Laboratoire de Chimie Théorique(UMR-CNRS 7616) Université Pierre et Marie Curie, Paris, France.
Inorganic Chemistry
|April 16, 2002
Summary
The electron localization function (ELF) analysis reveals hypervalent molecule bonding is similar to nonhypervalent molecules, with bond polarity determined by ligand electronegativity. Hypervalency primarily indicates more than four electron pair bonds, not a violation of bonding rules.
Area of Science:
- Quantum Chemistry
- Chemical Bonding Theory
- Computational Chemistry
Background:
- Hypervalent molecules, featuring central atoms with more than eight valence electrons, challenge traditional bonding models.
- The Valence Shell Electron Pair Repulsion (VSEPR) model provides a framework for predicting molecular geometry.
- Understanding electron distribution is key to characterizing chemical bonds.
Purpose of the Study:
- To investigate the nature of chemical bonding in hypervalent molecules using topological analysis.
- To correlate electron density distribution with molecular properties and bonding characteristics.
- To assess the significance of the 'hypervalent' designation in molecular bonding.
Main Methods:
- Topological analysis of the Electron Localization Function (ELF).
- Partitioning electron density into core and valence basins.
- Integration of electron populations within atomic basins.
Main Results:
- ELF analysis shows basin populations correlate with ligand electronegativity, varying significantly.
- Hypervalent atoms exhibit valence shell electron populations that differ from the octet rule, e.g., PF(5) vs. AsMe(5).
- Bonds in hypervalent molecules are analogous to those in nonhypervalent molecules, characterized by polarity.
Conclusions:
- The concept of hypervalency is primarily a descriptor of the number of bonds formed, rather than a fundamental deviation in bonding character.
- Bond polarity in hypervalent systems is dictated by ligand electronegativity, similar to Lewis octet molecules.
- ELF topological analysis provides a robust method for characterizing electron distribution and bonding in diverse molecular systems.