The Role of Recoupled Pair Bonding in Hypervalent Molecules

David E. Woon, Thom H. Dunning

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Hypervalence occurs when an element forms more bonds than expected based upon the number of unpaired electrons in the ground atomic state. Thus sulfur is hypervalent because compounds like SF4 and SF6 are stable, but oxygen is not hypervalent because the analogous compounds are not stable. In the recoupled pair bonding model, hypervalence occurs when lone-pair electrons such as the 3p and 3s pairs of ground state sulfur atoms can favorably participate in chemical bonds. Using sulfur fluoride species SFn (n=1-6) as an example, we show that this conditional form of bonding depends on the stability of the lone-pair in question and the ability of a given ligand to break up the pair. Recoupled pair bonding involves two steps, the initial formation of a bond that decouples a lone-pair and recouples one of the electrons in the lone-pair orbital with a electron in a singly occupied ligand orbital (recoupled pair bond), and the formation of a second bond as another ligand is coupled to the electron left over from recoupling (recoupled pair bond dyad). The first of these bonds is weaker than a covalent bond and its bond length is larger because of the adverse influence of the third electron. The second bond is usually stronger than a covalent bond and the two bond lengths are much closer to the bond lengths of the corresponding covalent bonds. The recoupled pair bond dyad has properties that distinguish it from a pair of covalent bonds. In this chapter, we use orbitals and other information from both multi-configurational self-consistent field (MCSCF) and approximate generalized valence bond (GVB) wavefunctions to demonstrate the bonding character of recoupled pair bonds and bond dyads. We also compare them to other models of hypervalency, such as the Rundle-Pimentel three-center, four-electron model.

Original languageEnglish (US)
Title of host publicationThe Chemical Bond
Subtitle of host publicationChemical Bonding Across the Periodic Table
PublisherWiley-Blackwell
Pages49-70
Number of pages22
Volume9783527333158
ISBN (Electronic)9783527664658
ISBN (Print)9783527333158
DOIs
StatePublished - Jul 8 2014

Keywords

  • Generalized valence bond
  • Hypervalence
  • Multi-configurational self-consistent field
  • Recoupled pair bonding
  • Sulfur and oxygen fluorides
  • Three-center four-electron model

ASJC Scopus subject areas

  • Chemistry(all)

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  • Cite this

    Woon, D. E., & Dunning, T. H. (2014). The Role of Recoupled Pair Bonding in Hypervalent Molecules. In The Chemical Bond: Chemical Bonding Across the Periodic Table (Vol. 9783527333158, pp. 49-70). Wiley-Blackwell. https://doi.org/10.1002/9783527664658.ch3