Charge-inverted Hydrogen Bonds Research Articles

Hydrogen bond types which do not fit accepted definitions.

There are various interactions that either partially fit or do not fit the currently accepted definitions of the hydrogen bond. However, they possess characteristics of this interaction. It seems that it is partly connected to the fact that these definitions are not precise. The typical 3c-4e (three centres - four electrons) A-H⋯B hydrogen bond is characterized by the single-atom A and B centres that are highly electronegative. On the other hand, non-typical interactions that do not fit the hydrogen bond definitions well are characterised by uncommon proton donors and/or proton acceptors. The cases of multi-centre proton acceptors, π-electron or σ-electron systems are well known - such interactions are designated as A-H⋯π and A-H⋯σ hydrogen bonds, respectively. However, the cases of interactions with the multi-centre proton donors and proton acceptors do not fit the majority of definitions of hydrogen bond. The π⋯H+⋯π system in the proton-bound homodimer of acetylene is an example. This system can be classified as a hydrogen bond according to the two-sites hydrogen bond, 2sHB, definition. There are various types of interactions discussed in this review; among them, those that are undoubtedly unclassified as hydrogen bonds, i.e., hydride bonds, and charge inverted hydrogen bonds, CIHBs. Special emphasis is also put here on the proton sponges and other systems such as the [FHF]- anion or [NgHNg]+ cation (Ng is the noble gas centre).

Si-H···Se Chalcogen-Hydride Bond Quantified by Diffraction and Topological Analyses.

The Si-H···Se contact in 1-mesitylselanyl-8-(dimethylsilyl)naphthalene (1), which exhibits the spatial arrangement of a δ-agostic interaction from geometric considerations, was investigated. Is this just enforced by close 1,8-proximity or is this a favorable interaction? Charge density studies are best suited to investigate the exact origin of the interaction and to quantify the properties. Hence, they are most elucidating. High-resolution X-ray diffraction data of 1 were collected, and a multipole refinement followed by a topological analysis using Bader's quantum theory of atoms in molecules was employed. The resulting bond properties were set in relation to high-level computational parameters. The comparison to Si-H···[M] agostics, hydride bonding, chalcogen bonds, and charge-inverted hydrogen bonds qualified the Si-H···Se noncovalent interaction to be best classified as a chalcogen-hydride bond.

Ten years of charge-inverted hydrogen bonds

This article is a review of the current state of knowledge about the so-called charge-inverted hydrogen bond—the type of interaction proposed 10 years ago. Numerous examples of model dimers and molecules in which this type of interaction exists in the inter- and intramolecular forms, respectively, as well as systems actually existing and studied by experimental and theoretical methods will be presented. The results of extensive theoretical research on the physical nature of charge-inverted hydrogen bonds will be thoroughly discussed. Dimers with a recently described hydride-carbene bond, i.e., a particular case of charge-inverted hydrogen bond in which the carbene carbon atom plays the role of an atom with the electron lone-pair vacancy, will also be presented.

The first theoretical proof of the existence of a hydride-carbene bond

We report the first theoretical proof of existance of dimers featuring hydride-carbene bond (Xδ+–Hδ-⋯⊃C), i.e. an interaction between partially negatively-charged hydrogen atom (i.e. a hydride hydrogen) and the unoccupied orbital p on the carbenic carbon (⊃C) atom in singlet carbenes. These interactions are special case of charge-inverted hydrogen bonds and are rather weak with binding and dissociation energies amounting to ca. 7.2–7.7 kJ/mol (1.7–1.8 kcal/mol) and 3.1–5.3 kJ/mol (0.7–1.3 kcal/mol), respectively.

Hydride-Triel Bonds.

In this article, we present the results of our comprehensive studies of 72 dimers of the R3XXH⋯YR3Y type (X = Si, Ge; Y = B, Al, Ga; RX = H, Cl, Me; RY = H, F, Cl, Me) and featuring hydride-triel bonds (i.e., charge-inverted hydrogen bonds). Influence of X and Y atoms as well as RX and RY substituents on various properties of these dimers is investigated in detail. In particular the strength of the H⋯Y hydride-triel bonds is paid a close attention and it is shown that hydride-triel bonds can be strong enough to considerably determine structure and properties of molecular systems. In addition, properties of the investigated dimers are largely governed by the charge transfer from the Lewis base to the Lewis acid, which is particularly important if more bulky and polarizable RY and Y atoms are present in the YR3Y molecule. Several excellent linear (R2 close to 1) and exponential correlations between pairs of diverse parameters are presented. Few instances are discussed where somewhat unexpected bond paths exist between two atoms featuring partial negative charges (e.g., between hydride hydrogen and halogen and between lateral sides of two halogens) showing that in some cases a bond path prefers to link two closely spaced electron-rich atoms instead of two atoms that are expected to form a bond. © 2018 Wiley Periodicals, Inc.

Revealing the physical nature and the strength of charge-inverted hydrogen bonds by SAPT(DFT), MP2, SCS-MP2, MP2C, and CCSD(T) methods

The physical nature of charge-inverted hydrogen bonds in H3 XH ⋯YH3 (X = Si, Ge; Y = Al, Ga) dimer systems is studied by means of the SAPT(DFT)-based decomposition of interaction energies and supermolecular interaction energies based on MP2, SCS-MP2, MP2C, and CCSD(T) methods utilizing dimer-centered aug-cc-pCVnZ (n = D, T, Q) basis sets as well as an extrapolation to the complete basis set limit. It is revealed that charge-inverted hydrogen bonds are inductive in nature, although dispersion is also important. Computed interaction energies form the following relation: EintSAPT<EintSCS-MP2≤EintMP2C<EintMP2≈EintCCSD(T). It is confirmed that the aug-cc-pCVDZ basis set performs poorly and that very accurate values of interaction and dispersion energies require basis sets of at least quadrupole-ζ quality. Considerably large binding energies suggest potential usefulness of charge-inverted hydrogen bonds as an important structural motif in molecular binding. Terminology applying to σ- and π-hole interactions as well as to triel and tetrel bonds is discussed. According to this new terminology the charge-inverted hydrogen bond would become the first described case of a hydride-triel bond. © 2017 Wiley Periodicals, Inc.

Comparative study of geometric and QTAIM-based differences between X[sbnd]H⋯Y intramolecular charge-inverted hydrogen bonds, M1⋯(H[sbnd]X) agostic bonds and M2⋯(η2-XH) σ interactions (X = Si, Ge; Y = Al, Ga; M1 = Ti, Co; M2 = Mn, Fe, Cr)

General conclusions on geometric and QTAIM-based differences and similarities between XH⋯Y intramolecular charge-inverted hydrogen bonds (IMCIHBs), M1⋯(HX) agostic bonds and M2⋯(η2-XH) σ interactions (X=Si, Ge; Y=Al, Ga; M1=Ti, Co; M2=Mn, Fe, Cr) are formulated. In particular we show that IMCIHBs feature significantly smaller covalent character as indicated, for example, by lower values of the electron density computed at BCPH⋯Y and lower values of δ(H,M). Some topological differences between IMCIHBs and the other interactions are found. Among others, it is shown that in agostic bonds and σ interactions nuclear attractors of H and M are more located in the H⋯M space and that bond paths tracing the XH bond are in many instances significantly curved toward RCP, whereas, on the contrary, the corresponding bond paths tracing XH in systems featuring IMCIHB are straight. Also the influence of the Si→Ge replacement was carefully studied, increasing the current state of knowledge on the chemistry of germanium.

Geometry- and QTAIM-Based Comparison of Intramolecular Charge-Inverted Hydrogen Bonds, M···(H-Si) "Agostic Bond", and M···(η(2)-SiH) σ Interactions.

Using large sets of systems having an intramolecular charge-inverted hydrogen bond (IMCIHB), M···(Ha-Si) "agostic bond" or M···(η(2)-SiH) σ interaction, we have compared both geometric and QTAIM-based topological parameters characterizing all these three types of interactions. It is shown that IMCIHBs can be distinguished from the other relevant interactions by the significantly less elongated Si-H bond. The other geometric parameters are not characteristic because they accept wide ranges of values in systems having either an M···(Ha-Si) "agostic bond" or M···(η(2)-SiH) σ interaction. If QTAIM-based results are investigated, then it is shown that an IMCIHB can be characterized by the position of the BCPH···M that is closer to the metal atom, whereas, quite the contrary, this BCP has been found to be closer to the agostic hydrogen in complexes having either M···(Ha-Si) or M···(η(2)-SiH) interactions. Another difference is in the curvature of the M···H bond path. If the M···H bond path tracing the M···(H-E) (E = Si, C) interaction is curved, then this curvature appears near the agostic hydrogen-a property particularly pronounced in M···(Ha-C) agostic bonds. Moreover, it has also been shown that an IMCIHB can be characterized by lower curvatures and, in general, lower values of the electron density computed at BCPH···Al than at BCPs of either M···(Ha-Si) or M···(η(2)-SiH) interactions. Importantly, IMCIHBs can be distinguished from the other two types of interactions on the basis of values of delocalization index, which are significantly lower for IMCIHBs. Other QTAIM-based parameters have occurred to be not characteristic for IMCIHBs due to wide ranges of their values obtained for M···(Ha-Si) and M···(η(2)-SiH) interactions. It has also been shown that the PBE0 functional gives the best molecular structure in comparison with experimental data.

QTAIM-based comparison of agostic bonds and intramolecular charge-inverted hydrogen bonds.

Using DFT-based calculations with seven exchange-correlation functionals (BP86, B3LYP, B3PW91, PBE0, TPSSh, M06-L, M06) we have performed comparative studies on α-, β-, γ-, and δ-agostic bonds (ABs) and intramolecular charge-inverted hydrogen bonds (IMCIHBs). Our detailed analysis of values of QTAIM parameters computed at bond (BCP) and ring critical points (RCP) as well as of the curvatures of bond paths tracing agostic bonds and intramolecular charge-inverted hydrogen bonds gives the opportunity to distinguish between both these types of interactions. In the case of molecules with agostic bonds, the BCP is significantly closer to the agostic hydrogen, whereas in systems with IMCIHB the BCP is, instead, somewhat closer to the metal atom. Agostic bonds are characterized by H···M bond paths being straight in the BCP···M section and then highly curved near the agostic hydrogen, whereas in the case of IMCIHB any substantial curvature of BP in the vicinity of hydrogen is not present. Quite the contrary, the significant curvature of BP near the metal atom can be obtained, instead. One can also distinguish IMCIHBs and ABs on the basis of values of bond ellipticity at BCP and the electron density at RCP which are either somewhat (PBE0) or considerably (M06) greater for the latter type of interaction. It has also been shown that, in general, the exchange-correlation functional has small influences on most of QTAIM parameters computed at BCP and RCP. More significant influences have only been obtained for Laplacian of the electron density, some its components, and the bond ellipticity.

Charge-inverted hydrogen bond vs. other interactions possessing a hydridic hydrogen atom

By performing ab initio calculations for a wide range of dimers with various types of interactions involving a hydridic hydrogen atom (hydride hydrogen bond, dihydrogen bond, agostic bond, etc.) we show that the recently proposed charge-inverted hydrogen bond (CIHB) should indeed be investigated as a new type of interaction. This conclusion is obtained on the basis of formal definitions of relevant interactions as well as on the quantum theory of atoms in molecules and the hybrid variational-perturbation scheme of the decomposition of the interaction energy. Additionally, it is shown that CIHB is somewhat similar to strong dihydrogen bonds. The origin of this finding is also presented.

Physical nature of interactions in charge-inverted hydrogen bonds

Based on the hybrid variational-perturbation decomposition scheme we show that the electrostatic and delocalization energy terms are the most stabilizing components of the interaction energy of the charge-inverted hydrogen-bond (CIHB). It is shown that the electrostatic multipole term is the only one that closely reproduces the MP2 minimum conformation thus indicating that the bent structure results from a peculiar distribution of charge that can be described by atomic multipole moments of interacting monomers. To isolate the origin of observed bending of CIHB idealized linear structures have been analyzed as well. In this case the delocalization energy term outweighs all other stabilizing terms.

Theoretical insight into the nature of the intermolecular charge-inverted hydrogen bond

The results of our further theoretical studies on the so-called charge-inverted hydrogen bond that is defined as an interaction between the partially negatively charged hydrogen atom of the X–H subunit and an atom possessing a lone pair vacancy are presented. It is shown that the elongation of the X–H bond and the red-shift of its stretching vibration frequency is caused by the charge transfer from the bonding σXH orbital to the empty pz orbital of the Y atom. The weakening of the X–H bond can also be reinforced by the small increase of the occupancy of the σXH★ antibonding orbital. Based on quantum theory of atoms in molecules by Bader it is shown that the charge-inverted hydrogen bond is a closed-shell type interaction with significant contribution of covalent character. We found charge-inverted hydrogen bonds as a new type of interactions which are different than more common hydride or agostic-type interactions.

Full vs. constrain geometry optimization in the open–closed method in estimating the energy of intramolecular charge-inverted hydrogen bonds

We investigate several variants of the open–closed method to estimate the energy of the intramolecular charge-inverted hydrogen bond in model systems. We show that, depending on whether the geometry of the reference open system is partially or fully optimized, the estimated value of the energy may be from a wide range. It seems that the most reasonable reference system should have geometry parameters optimized but with the simultaneous freezing of those geometry parameters whose relaxation may lead to the significant change in the bonding pattern. Results obtained by means of two other estimating methods are studied. Reasonable estimates of energy values can be obtained only if full geometry optimizations of the molecules being components of the isodesmic reaction do not lead to any significant difference in the bonding pattern comparing with that of the interaction-bonded system. All calculations were performed using the B3LYP/aug-cc-pVTZ approximation.

Intramolecular charge-inverted hydrogen bond

It is shown that the Si δ + H δ - ⋯ ⊃ Al interaction, where ‘ ⊃ ’ denotes the electron lone-pair vacancy, may exist if Si δ + H δ - and ⊃ Al subunits belong to the same molecule, i.e. they may form the intramolecular charge-inverted hydrogen bond. Its influence to the molecular geometry is studied by comparison with geometries of several reference systems. In studied molecules this kind of interaction is formed even if it leads to large structural deformations of the system and is even energetically profitable in the case of the presence of strong strain forces in the five-membered quasi-ring molecule.

Binding of X–H to the lone-pair vacancy: Charge-inverted hydrogen bond

It is found that in certain cases the X–H bonds of the X δ + – H δ - polarity may weakly interact with lone pair vacancies in Y ( ⊃ Y ), leading to weak X δ + – H δ - ⋯ ⊃ Y structures. These structures, which are referred to as charge-inverted hydrogen bonds (CIHB), were computationally established for several pairs of X δ + – H δ - donors and hydrides of the 13th group of the periodic table and shown to feature the characteristics of the usual hydrogen bonds.