The ethyl cation as proton donor for dihydrogen bonds in the (m=1 or 2 and n=1 or 2) complex: A theoretical study

Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides

The dihydrogen bond-an interaction between a transition-metal or main-group hydride (M-H) and a protic hydrogen moiety (H-X)-is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen exchange, alcoholysis and aminolysis, hydrogen evolution, hydrogenation, and dehydrogenation, are discussed.

A comparative interplay between small heterorings and hypofluorous acids

Through the B3LYP/6-311++G(d,p) calculations, theoretical studies of structural parameters, electronic properties, infrared vibration modes, and charge density topologies on the C2H4O∙∙∙HX and C2H5N∙∙∙HX (X = F or O-F) heterocylic hydrogen complexes are presented. The H-bond distances and high energies point out strong contacts and stable interactions in these complexes, and the relationships between the frequency shifts on the H-F and H-O bonds as well as O-F σ-holes with the interaction strength are the benchmarks of this current work. The computations of charge transfer amounts in light of the ChelpG and NBO approaches revealed a separation of charge density on the O-F σ-holes, whose statement is reinforced by the QTAIM descriptors. Despite that O∙∙∙H and N∙∙∙H H-bonds have been characterized as closed-shell interactions, qualitatively the appearance of a partial covalent profile also was unveiled by the QTAIM protocol.

The covalence and infrared spectra of cationic hydrogen bonds and dihydrogen bonds

A theoretical study of hydrogen bonds and dihydrogen bonds formed by ethyl cation, hydrocarbons and magnesium hydride is presented with calculations performed at the BHandHLYP/6-31G(d,p) level of theory. The structural results and IR analyses demonstrated great insights, mainly the strengthening and weakness of the CC bond of the ethyl cation and π or pseudo-π bonds, respectively. The interaction strength was measured through the supermolecule as well as by means of additional approaches. The QTAIM calculations were applied to characterize not only the intermolecular interactions but specifically the covalent character in the H + ⋯ π, H + ⋯ pseudo-π and H + ⋯ H contacts. The NBO calculations were useful to interpret the polarization on the CC bond and whether this effect is related with the bond length reduction as well as increase of charge density and frequency shifts.

Theoretical Study of Mixed Hydrogen and Dihydrogen Bond Interactions in Clusters

Ab initio calculations were used to analyze interactions of with 1–4 molecules of NH3at the MP2/6-311++G(d,p) and the B3LYP/6-311++G(d,p) computational levels. In addition to H3B–H⋯H–NH2dihydrogen bond, the H2N–H⋯NH3hydrogen bonds were also predicted in clusters. Negative cooperativity in clusters constructed from mixed H3B–H⋯H–NH2dihydrogen and H2N–H⋯NH3hydrogen bonds are more remarkable. The negative cooperativity increases with size and number of hydrogen bonds in cluster. The B–H stretching frequencies show blue shifts with respect to cluster formation. Greater blue shift in stretching frequencies was predicted for B–H bonds which did not contribute to dihydrogen bonding with NH3molecules. The structures were analyzed with the atoms in molecules (AIM) methodology.

Bonding topology, hydrogen bond strength, and vibrational chemical shifts on hetero-ring hydrogen-bonded complexes — Theoretical insights revisited

This work presents a theoretical study about the interaction strength of the hydrogen-bonded complexes C2H4O···HF, C3H6O···HF, C2H4O···HCF3, and C3H6O···HCF3 at the B3LYP/6–311++G(d,p) level. The structures, hydrogen bond energies, charge transfers, and dipole moments of these complexes were analyzed in accordance with routine spectroscopy events, such as the red- and blue-shifts on the stretch frequencies of the proton donors (HF and HCF3). The ChelpG atomic charges were used to quantify the charge-transfer fluxes from electron donor (O) towards to acceptors (HF or HCF3). Moreover, the topological calculations on the basis of the quantum theory of atoms in molecules (QTAIM) approach were also used to unveil the hydrogen bond strength (O···H), mainly in the determination of their electronic densities and Laplacian shapes.

Theoretical aspects of binary and ternary complexes of aziridine···ammonia ruled by hydrogen bond strength

B3LYP calculations, ChelpG atomic charges, and quantum theory of atoms in molecules (QTAIM) integrations were used to investigate the binary (1:1) and ternary (1:2) hydrogen-bonded complexes formed by aziridine (1) and ammonia (2). In a series of analysis, geometry data, electronic parameters, vibrational oscillators, and topological descriptors were used to evaluate hydrogen bond strength, and additionally to determine the more prominent molecular deformations upon the formation of C(2)H(5)N···NH(3) (1:1) and C(2)H(5)N···2NH(3) (1:2) systems. Taking a spectroscopic viewpoint, results obtained from analysis of the harmonic infrared spectrum were examined. From these, new vibrational modes and red- and blue-shifts related to the stretch frequencies of either donors or acceptors of protons were identified. Furthermore, the molecular topology of the electronic density modeled in accord with QTAIM was absolutely critical in defining bond critical points (BCP) and ring critical points (RCP) on the heterocyclic structures. Taking all the results together allowed us to identify and characterize all the N···H hydrogen bonds, as well as the strain ring of the aziridine and its stability.

A theoretical study of dihydrogen bonds in small protonated rings: aziridine and azetidine cations

B3LYP/6-311++G(d,p) calculations were used to predict some molecular properties of the C2H6N+...BeH2, C2H6N...MgH2, C3H8N...BeH2 and C3H8N+...MgH2 dihydrogen-bonded complexes. In these systems, it was demonstrated that the C2H6N+ and C3H8N+ protonated rings are potential candidates to bind with protonic hydrogens derived from alkaline earth metal compounds, BeH2 and MgH2. In terms of structural parameters and quantification of the dihydrogen bond energies, we should mention that the C2H6N+ three-membered ring provides the formation of stronger bound systems, which are 4.0 kJ mol-1 more stables than C3H8N+ four-membered ones. As complement, the analysis of the infrared spectrum indicated that red-shifts and blue-shifts are occurring in the N-H bonds of both C2H6N+ and C3H8N+ cationic rings. However, these two vibrational shifts were also verified on BeH2 and MgH2, what lead us to affirm that cationic compounds derived from small nitrogen rings and earth alkaline molecules are able to form unusual dihydrogen-bonded complexes by means of distinct spectroscopic phenomena, the red-shits and blue-shifts.