General method for the development of models of electronic structure and bonding: covalent bonds, recoupled pair bonds and through-pair interactions

Generalized Valence Bond (GVB) Theory;Recoupled pair bond;Recoupled pair bond dyad;Bonding

Takeshita, Tyler Young

关键词: Generalized Valence Bond (GVB) Theory;    Recoupled pair bond;    Recoupled pair bond dyad;    Bonding;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/78748/TAKESHITA-DISSERTATION-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The concept of the chemical bond is essential to our understanding of molecular phenomena. G. N. Lewis laid the groundwork for our understanding of chemical bonds nearly a century ago in his classic 1916 paper in the Journal of the American Chemical Society, “The Atom and the Molecule.” This model was given a firm theoretical foundation by W. Heitler and F. London shortly after the discovery of quantum mechanics. The 1930s were most fruitful with the formulation of valence bond theory by L. Pauling, G. W. Wheland and J. C. Slater and molecular orbital theory by F. Hund and R. S. Mulliken. However, in spite of significant advances in both computational and experimental methods, little progress has been made in the development of rigorous conceptual models of electronic structure based on high-level solutions of the molecular Schrödinger equation. In this dissertation a novel method for the general and systematic development of comprehensive electronic structure models is introduced. This computationally driven design approach is applied to refine our understanding of generalized valence bond (GVB) theory and to the development of the recoupled pair bonding model. The recoupled pair bond model consists of two conceptual components, the recoupled pair bond and the recoupled pair bond dyad.The fundamental aspects of the recoupled pair bond, where the electrons that compose an atomic or molecular lone pair is recoupled, are introduced through the analysis of the ground, 2Π, and low-lying excited, 4Σ–, states of CF, OF and SF. It is shown that the conditional nature of recoupled pair bonds formed with 2p and 3p lone pairs, but not 2s lone pairs, is straightforward in the framework of GVB theory and is largely governed by the Pauli exclusion principle and can be correlated with the correlation of the lone pair and electronegativity of the ligand. Knowledge of the presence or absence of recoupled pair bonds offer valuable insights into the available ligand addition pathways a molecular species may participate in. In the presence of a recoupled pair bond one such addition pathway is the formation of a recoupled pair bond dyad. The ground and excited states of CF2 and SF2 are used to show that the formation of a recoupled pair bond dyad is also well predicted by the spatial correlation of the orbitals involved and the electronegativity of the ligand.Application of the model in conjunction with an atom-by-atom approach, that constructs molecules of increasing complexity through the systematic addition of atoms, shows that the recoupled pair bonding model is extremely general and accounts for many aspects of the anomalous behavior of the late p-block elements beyond the first row. In this dissertation this model is also used to rationalize the electronic structure of two pairs of molecules, NXOH and XO2, X = O or S, where the molecules in each pair differ by one valence isoelectronic atom yet display vastly different properties. It is found that the perplexing behavior of these valence isoelectronic species is accounted for by the presence or absence of recoupled pair bonds, recoupled pair bond dyads and through-pair interactions.