QTAIM Study of Strong H-Bonds with the O−H···A Fragment (A = O, N) in Three-Dimensional Periodical Crystals

Abstract

The relationship between the d(H...A) distance (A=O, N) and the topological properties at the H...A bond critical point of 37 strong (short) hydrogen bonds occurring in 26 molecular crystals are analyzed using the quantum theory of atoms in molecules (QTAIM). Ground-state wave functions of the three-dimensional periodical structures representing the accurate experimental geometries calculated at the B3LYP/6-31G** level of approximation were used to obtain the QTAIM electron density characteristics. The use of an electron-correlated method allowed us to reach the quantitatively correct values of electron density rhob at the H...A bond critical point. However, quite significant differences can appear for small absolute values of the Laplacian (<0.5 au). The difference between the H...O and H...N interactions is described using the rhob versus d(H...A) dependence. It is demonstrated that the values of parameters in this dependence are defined by the nature of the heavy atom forming the H...A bond. An intermediate (or transit) region separating the shared and closed-shell interactions is observed for the H-bonded crystals in which the bridging proton can move from one heavy atom to another. The crystalline environment changes the location of the bridging proton in strong H-bonded systems; however, the d(O-H)/d(H...O) ratio is approximately the same for both the gas-phase complexes and molecular crystals with a linear or near-linear O-H...O bond.

Universal Features of the Electron Density Distribution in Hydrogen‐Bonding Regions: A Comprehensive Study Involving H⋅⋅⋅X (X=H, C, N, O, F, S, Cl, π) Interactions

“…[16,17] Similar dependencies for HBs have been observed in crystals from experimental electron density distributions determined by using high-resolution Xray diffraction data [12,[18][19][20] of from theoretical calculations. [21] In the analysis of these dependencies, typically through least squares fits, the values of the properties at the BCP present some degree of dispersion around the fitting curves. When using experimental data, this dispersion is usually attributed to observational errors, which correspond to the difference between the experimentally determined and the exact magnitude of 1(r) and affect the derived topological and energetic properties at BCP.…”

DFT study of H-bonds in the peptide secondary structures: The backbone–side-chain and polar side-chains interactions

“…The quantum-topological analysis of the crystalline electron density was performed by the TOPOND computer program [31]. Details of the electron-density topological analysis of the periodical models were presented elsewhere [32].…”

“…Computed values of the OAH distance of 1.021 Å and the electron density at the H-bond critical point of $0.05 a.u. indicate the ''intermediate" type of non-covalent interactions, which is placed between the ideal shared (covalent) and closedshell interactions [32]. Table 4 shows that the polar side-chain interactions cause the formation of moderate inter-chain H-bond ($40 kJ/mol).…”

Synthesis, Spectral Studies and Quantum-Chemical Investigations on the Powerful Fluorophores: Imidazo[4,5-a]acridines

“…If both ∇ 2 ρ and H C be simultaneously positive (∇ 2 ρ(r) > 0, H c > 0) which can be categorized as the interactions of closed electron shells, to which, in particular, most hydrogen bonds and van der Waals interactions belong. If ∇ 2 ρ be positive while H C is negative, and the -G C /V C is smaller than 1, then the nature of interaction is considered as partly covalent [22].…”