Kinetic Energy Density as a Predictor of Hydrogen-Bonded OH-Stretching Frequencies

Abstract

This work considers the nature of the intermolecular hydrogen bond in a series of 15 different complexes with OH donor groups and N, O, P, or S acceptor atoms. To complement the existing literature, room-temperature gas-phase vibrational spectra of the methanol-pyridine, ethanol-pyridine, and 2,2,2-trifluoroethanol-pyridine complexes were recorded. These complexes were chosen, as they exhibit hydrogen bonds of intermediate strength as compared to previous investigations that involved strong or weak hydrogen bonds. Non Covalent Interactions (NCI) theory was used to calculate various properties of the intermolecular hydrogen bonds, which were compared to the experimental OH-stretching vibrational red shifts. We find that the experimental OH-stretching red shifts correlate strongly with the kinetic energy density integrated within the reduced density gradient volume that describes a hydrogen bond [G(s)]. Given that vibrational red shifts are commonly used as a metric of the strength of a hydrogen bond, this suggests that G(s) could be used as a predictor of hydrogen bonding strength.

Halogen Bonding: A Halogen-Centered Noncovalent Interaction Yet to Be Understood

“…A necessary condition is the existence of a bond path and a bcp between the two atoms under consideration; a sufficient condition is a negative value of the local energy density H(r) = V(r) + G(r) at the bcp, which implies a dominating potential energy V(r) (always negative, stabilizing) over the kinetic energy G(r) (always positive, destabilizing), and is indicative of a covalent interaction. These signatures are not only true for hydrogen bonds [252], but also for halogen bonds, tetrel bonds, chalcogen bonds, pnictogen bonds, and any other noncovalent interaction, and including metal-ligand coordinate interactions of various types [253,254].…”

Structure-directing sulfur...metal noncovalent semicoordination bonding

“…The most common real-space method, the Quantum Theory of Atoms in Molecules (QTAIM) (Matta & Boyd, 2007), provides an opportunity to explore bonding diatomic interactions with meaningful exchange energy contributions and subsequently to construct the atomic connectivity graph. The properties of corresponding descriptors of topological bonding, such as interatomic surfaces and (3, À1) critical points (CPs) of electron density (r), serve as weights of the connectivity graph and are frequently used to provide a range diatomic interactions in terms of charge separation and contributions to the energy of the system (Bader & Essé n, 1984;Cremer & Kraka, 1984;Silva Lopez & de Lera, 2011;Alkorta et al, 1998;Espinosa et al, 1998;Vener et al, 2012;Bartashevich, Matveychuk et al, 2014;Saleh et al, 2015;Lane et al, 2017;Ananyev et al, 2017;Borissova et al, 2008;Romanova et al, 2018). For instance, the topographic analysis of (r) in the transition metal complexes usually indicates the MÁ Á ÁX bonding interaction for any coordination bond, i.e.…”

Estimations of energy of noncovalent bonding from integrals over interatomic zero‐flux surfaces: Correlation trends and beyond

“…), the E B ∼ g ( r bcp ) correlation ( g ( r bcp ) denotes Lagrangian electronic kinetic energy density at bcp ) established for hydrogen bonds and further extended on a wider range of noncovalent interactions (see, ref. ), the Δ ν ∼ g ( r ) RDG correlation (RDG—reduced density gradient, g ( r ) RDG denotes integral of electronic kinetic energy density within a specific isosurface of the RDG function, Δ ν —shift of a vibration band upon the interaction formation/breaking) for hydrogen bonds, the E B ∼ v ( r ) RDG and E B ∼ g ( r ) RDG correlations for various weak interactions …”

“…Each E B ∼ ρ ( r bcp ) correlation was developed for a particular interaction type, for which it is known that the ρ ( r bcp ) and v ( r bcp ) values are interconnected and depend only on internuclear separation. Moreover, if it is believed that the local quantity at bcp is a measure of the integral of this quantity over the region around this bcp , than the Δ ν ∼ g ( r ) RDG , E B ∼ g ( r ) RDG and E B ∼ v ( r ) RDG correlations can also be considered as special cases of the general k eff trend. Again, the v ( r ) and g ( r ) values are interconnected through the local virial theorem, while the red shifts of the XH stretching vibrational frequency are nearly quantitatively equal to changes of the XH stretching force constant since the reduced mass of the XH stretching vibration is close to unity (for instance for X = O μ ≈ 0.94 a.m.u.)…”

“…This kind of analysis is also attractive as the ρ ( r ) function can readily be calculated using wavefunction or density functional theories or even can be constructed from experimental diffraction data from long‐ordered solids such as crystals . Various features, which can be calculated at bcp and around it, are usually analyzed to describe an interaction in terms of its ionic/covalent character, directionality and finally, strength …”