Chemical bonding is crucial to the material world, influencing everything from basic atoms to intricate universes. It involves the attractive forces between atoms, ions, or molecular fragments. It was first introduced by Gilbert N. Lewis in 1916, with subsequent developments by Irving Langmuir and breakthroughs in 1927 when Heitler and London used quantum theory to explain the H2 molecule's chemical bond. Linus Pauling later combined classical and quantum viewpoints to create a new perspective on chemical bonding1. Chemical bonds exhibit considerable variability, influenced by factors such as electronegativity, atomic size, and electron density distribution. Lines typically represent covalent bonds, whereas dative bonds, introduced by Sidgwick in 1923, were devised to characterise coordinative compounds. Advanced computational methods like the EDA-NOCV method combine Energy Decomposition Analysis (EDA)2 with Natural Orbitals for Chemical Valence (NOCV)3 to provide the flexibility to study the interacting fragment in more than one possible electron configuration and charge. Thus, enables precise analysis of bonding energies, including the energy required to deform fragments and their valence electronic configuration (ΔΕprep) and the interaction energy between fragments (ΔΕint), further divided into electrostatic, Pauli repulsion, orbital interaction, which are sometimes augmented by a fourth expression for dispersion (van der Waals) interactions. The most accurate ΔΕint values directly relate to experimental bond dissociation energy (-De = ΔΕint + ΔΕprep). The further partitioning of the orbital (covalent) term into pairwise orbital interactions has been proven very helpful because it provides a quantitative expression of the FMO model of Fukui and the suitable orbitals of the interacting fragment for the most accurate description of the chemical bond1. Therefore, my goal is to present in a clear and concise way what we currently understand of the physical nature of the interatomic interactions that give rise to what we call a chemical bond, highlight the most important findings from numerous studies to provide an overview of unique bonding patterns in different sets of molecules using computational methods, such as EDA-NOCV, in conjunction with NBO and QTAIM within the framework of Density Functional Theory (DFT).
References:
[1]. Zhao, L.; Pan, S.; Holzmann, N.; Schwerdtfeger, P.; Frenking, G. Chemical Bonding and bonding models of main-group compounds. Chem. Rev. 2019, 119, 8781-8845.
[2]. Ziegler, T.; Rauk, A. On the calculation of bonding energies by the Hartree Fock Slater method. Theor. Chim. Acta 1977, 46, 1–10.
[3]. Mitoraj, M.; Michalak, A. Donor-Acceptor Properties of Ligands from the Natural Orbitals for Chemical Valence Organometallics 2007, 26, 6576 – 6580.