Atoms‐in‐Molecules Analysis of Extended Hypervalent Five‐Center, Six‐Electron (5c–6e) C₂Z₂O Interactions at the 1,8,9‐Positions of Anthraquinone and 9‐Methoxyanthracene Systems

Abstract

To clarify the nature of five‐center, six‐electron (5c–6e) C2Z2O interactions, atoms‐in‐molecules (AIM) analysis has been applied to an anthraquinone, 1,8‐(MeZ)2ATQ (1 (Z=Se), 2 (Z=S), and 3 (Z=O)), and a 9‐methoxyanthracene system, 9‐MeO‐1,8‐(MeZ)2ATC (4 (Z=Se), 5 (Z=S), and 6 (Z=O)), as well as 1‐(MeZ)ATQ (7 (Z=Se), 8 (Z=S), and 9 (Z=O)) and 9‐MeO‐1‐(MeZ)ATC (10 (Z=Se), 11 (Z=S), and 12 (Z=O)). The total electronic energy density (Hb(rc)) at the bond critical points (BCPs), an appropriate index for weak interactions, has been examined for 5c–6e C2Z2O and 3c–4e CZO interactions of the np(O)⋅⋅⋅σ*(ZC) type in 1–12. Some hydrogen‐bonded adducts were also re‐examined for convenience of comparison. The total electronic energy densities varied in the following order: O⋅⋅⋅O (3: Hb(rc)=0.0028 au)=O⋅⋅⋅O (6: 0.0028 au)>O⋅⋅⋅O (9: 0.0025 au)≥NN⋅⋅⋅HF (0.0024 au)≥O⋅⋅⋅O (12: 0.0023 au)≫H2O⋅⋅⋅HOH (0.0015 au)>S⋅⋅⋅O (8: 0.0013 au)=S⋅⋅⋅O (2: 0.0013 au)≥S⋅⋅⋅O (11: 0.0012 au)=S⋅⋅⋅O (5: 0.0012 au)>HF⋅⋅⋅HF (0.0008 au)=Se⋅⋅⋅O (10: 0.0008 au)=Se⋅⋅⋅O (4: 0.0008 au)≥Se⋅⋅⋅O (1: 0.0007 au)≥Se⋅⋅⋅O (7: 0.0006 au)≫HCN⋅⋅⋅HF (−0.0013 au). Hb(rc) values for S⋅⋅⋅O were predicted to be smaller than the hydrogen bond of H2O⋅⋅⋅HOH and Hb(rc) values for Se⋅⋅⋅O are very close to or slightly smaller than that for HF⋅⋅⋅HF in both the ATQ and 9‐MeOATC systems. In the case of Z=Se and S, Hb(rc) values for 5c–6e C2Z2O interactions are essentially equal to those for 3c–4e CZO if Z is the same. The results demonstrate that two np(O)⋅⋅⋅σ*(ZC) 3c–4e interactions effectively connect through the central np(O) orbital to form the extended hypervalent 5c–6e system of the σ*(CZ)⋅⋅⋅np(O)⋅⋅⋅σ*(ZC) type for Z=Se and S in both systems. Natural bond orbital (NBO) analysis revealed that ns(O) also contributes to some extent. The electron charge densities at the BCPs, NBO analysis, and the total energies calculated for 1–12, together with the structural changes in the PhSe derivatives, support the above discussion.

A Unique Case of Oxidative Addition of Interhalogens IX (X=Cl, Br) to Organodiselone Ligands: Nature of the Chemical Bonding in Asymmetric ISeX Polarised Hypervalent Systems

“…[29] Analysis of the QTAIM properties at the BCPs of Se À C/ Se À X bonds in 1-17: To better establish the degree of hypervalency of the selenium atom in chalcogen compounds featuring either a linear I À SeA C H T U N G T R E N N U N G ( À C<) À X (X= Br, Cl) or linear NCÀSeA C H T U N G T R E N N U N G (ÀC<)ÀI moiety and, therefore, the 3c-4e nature of these compounds, we performed a topological electron density analysis on model compounds 1-17 (Scheme 2) based on the quantum theory of atoms-in-molecules (QTAIM) [30] approach developed by Bader and already applied with success to other types of hypervalent systems. [31][32][33][34][35] Non-hypervalent compounds 1-5 have also been considered as reference compounds for comparing QTAIM parameters (see below). The structures of 6-17 were previously optimised at the DFT level by using the LanL2DZ basis set with effective core potentials (ECP) for halogen atoms, [14b, 17, 23a] but in this work d,p polarisation functions were also added.…”

COOPERATIVITY BETWEEN HYDROGEN BOND AND HALOGEN BOND INHBr⋯BrX⋯HBr (X = F, Cl, Br)

“…68 According to the theory, the electron density is used to describe the strength of a bond. The larger value means the stronger bond.…”

Intrinsic Dynamic Nature of Neutral Hydrogen Bonds Elucidated with QTAIM Dual Functional Analysis: Role of the Compliance Force Constants and QTAIM‐DFA Parameters in Stability

“…The QTAIM approach, introduced by Bader, enables us to analyze the nature of chemical bonds and interactions . Many QTAIM investigations have been reported, mainly by theoretical researchers, and experimental scientists have recently used QTAIM to explain their results by considering chemical bonding and interactions . A bond critical point (BCP, ✶) is an important concept in QTAIM, for which ρ ( r ) (charge density) reaches a minimum along the interatomic (bond) path, whereas it is a maximum on the interatomic surface separating the atomic basins.…”