Here, we discuss that unlike bond dissociation energy (BDE) that is a state function quantity, the energy components of the energy decomposition analysis (EDA), i.e. electrostatic interaction, Pauli repulsion, and orbital interaction, are path (process) function quantities. Being a path function means that EDA energy components are not uniquely defined, i.e. the relative magnitudes of the orbital interaction, Pauli repulsion, and electrostatic components may vary depending on the selected pathway for EDA. Therefore, at best, EDA can define whether closely related chemical bonds are more or less ionic/covalent compared with each other. However, a precise assessment of the nature of a certain type of chemical bond using EDA is a questionable task. Besides, we briefly discuss that the widely used EDA pathway, which is merely an arbitrary choice among infinite possible paths, comes to conclusions not consistent with our widely accepted knowledge of bond formation even for the simplest molecules.

This article examines the electronic structure of group 2 (E = Be and Mg) ligand stabilized compounds. We elaborate on the donor–acceptor interaction L(0) ⇆ E(0) ⇆ L(0) and diradical L(−1) → E(+2) ← L(−1) pictures to assess the oxidation state of the metal.

A theoretical study of the hydrolysis mechanism of A-234 [EtO–P(O)(F)–NC(Me)–N(Et)₂]; the suspected novichok agent in the Skripal attack.

Quantum chemical calculations using ab initio methods at the CCSD(T)/def2-TZVPP level and density functional theory using BP86 and M06-2X functionals in conjunction with def2-TZVPP basis sets have been carried out on the title molecules. The calculated energies suggest that the N-oxides R₃NO with R = F, Cl are lower in energy than the amine isomers R₂NOR, but the latter form is more stable than the N-oxides when R = H, Me, Ph. In contrast, the phosphane oxides R₃PO are always more stable than the phosphanyl isomers R₂NOR except for the parent system with R = H, where the two isomers are close in energy. The energy decomposition analysis suggests that the best description of the N–O bond in N-oxides R₃NO depends on the nature of the substituent R. The halogen systems F₃NO and Cl₃NO and the triphenyl species Ph₃NO possess dative bonds R₃N→O, which are enhanced by R₃N←O π backdonation. The contribution of the π backdonation is only 10% of the total orbital interactions ΔE_orb in Ph₃NO, but it amounts to ∼22% of ΔE_orb in F₃NO and Cl₃NO. The N–O bonds H₃NO and Me₃NO are better described in terms of electron-sharing single bonds between charged fragments R₃N⁺–O⁻, which are supported by modest R₃N⁺←O⁻ π backdonation that comprise 13–16% of ΔE_orb. In contrast, all phosphane oxides R₃PO are best depicted with electron-sharing single bonds between charged fragments R₃P⁺–O⁻, which are significantly supported by R₃P⁺←O⁻ π backdonation contributing 22–32% of ΔE_orb.

A recent article by Pan and Frenking challenges our assignment of the oxidation state of low valent group 2 compounds. With this reply, we show that our assignment of Be(+2) and Mg(+2) oxidation states in Be(cAAC^Dip)₂ and Mg(cAAC^Dip)₂ is fully consistent with our data. Some of the arguments exposed by Pan and Frenking were based on visual inspection of our figures, rather than a thorough numerical analysis. We discuss with numerical proof that some of the statements made by the authors concerning our reported data are erroneous. In addition, we provide further evidence that the criterion of the lowest orbital interaction energy in the energy decomposition analysis (EDA) method is unsuitable as a general tool to assess the valence state of the fragments. Other indicators based on natural orbitals for chemical valence (NOCV) deliver a more reliable bonding picture. We also emphasize the importance of using stable wavefunctions for any kind of analysis, including EDA.