Computational study of the cooperative effects between tetrel bond and halogen bond in XCN⋅⋅⋅F2CO⋅⋅⋅YCN complexes (X = H, F, Cl, Br; Y = F, Cl, Br)

Theoretical Insights into Regulation of Red/Blue-Shifting Hydrogen Bonds Through Cooperativity with Regium Bonds

To deeply understand the characteristics and regulation of red/blue-shifting hydrogen bonds (HBs), a theoretical investigation was conducted to explore the cooperativity between regium bonds and HBs in the complexes of Y···MCN···HCX3 (M = Cu, Ag, Au; Y = H2O, HCN, NH3; X = F, Cl). When MCN formed a hydrogen bonding dimer with CHF3 or CHCl3, the blue shift of C-H vibration frequency v(C-H) decreases as the following sequence Au > Cu > Ag, and the red shift decreases following the order Ag > Cu > Au. Upon the formation of ternary complexes, the presence of regium bonding interactions exerts a positive synergistic effect, resulting in the strengthening of the HBs. This, in turn, leads to noticeable changes in the red and blue shifts of v(C-H). In CHF3 complexes, v(C-H) undergoes a decrease in the blue shift, whereas that in CHCl3 exhibits an increase in the red shift. Especially, a transition from blue to red shift is observed within the AuCN···HCCl3 complex. As the strength of the regium bond increases, the trend of shifting from blue to red becomes more pronounced. For a given MCN, the changes occur in the order of NH3 > HCN > H2O. The interplay between two interactions was revealed by the molecular electrostatic potentials (MEP), the atoms in the molecule (AIM), and natural bond orbitals (NBO) analysis. It is revealed that Δv(C-H) is linearly correlated with a series of configuration and energy parameters. We explain the red- and blue-shifting HBs and their changes from the perspective of hyperconjugation and rehybridization. The presence of the positive synergistic effect enhances the hyperconjugation effect, thereby leading to a reduction in the blue shift and an increase in the red shift of v(C-H) within the complexes. This study enriches previous mechanisms regarding red- and blue-shifting HBs and introduces a novel idea to manipulate the characteristics of HBs, with the potential to impact the functioning of intricate systems.

Can we quantitatively evaluate the mutual impacts of intramolecular metal-ligand bonds the same as intermolecular noncovalent bonds?

In this paper, we have reviewed several equations for calculating the cooperative energy of two chemical bonds between three fragments/species, regardless of whether they are atoms, ions or molecules, and whether the bonds between them are intra- or intermolecular. It is emphasized that two chemical bonds upon cooperation in a new compound change the bond dissociation energy of each other exactly by the same quantitative value, their cooperative energy, regardless of the nature of the bonds or whether one bond is very weak and another one is very strong. However, the final benefit/drawback of weak bonds from this cooperation can be considerably larger than that of strong bonds. The above statements are supported by a computational study on the various types of inter- and intramolecular chemical bonds.

Cooperativity between H-bonds and tetrel bonds. Transformation of a noncovalent C⋯N tetrel bond to a covalent bond

The dimers and trimers formed by imidazole (IM) and F2TO (T = C, Si, Ge) are studied by ab initio calculations. IM can engage in either a NH⋯O H-bond with F2TO or a T⋯N tetrel bond (TB) with the π-hole above the T atom. The latter is a true noncovalent TB for T = C but is a much shorter and stronger covalent bond with F2SiO or F2GeO. When a second IM is added, the cooperativity emerging from its H-bond with the first IM makes it a stronger nucleophile, leading to two minima with F2CO. The first structure contains a long noncovalent C⋯O TB and there is a much shorter covalent bond in the other, with a small energy barrier separating them. The same sort of double minimum occurs when the two IM units are situated parallel to one another in a stacked geometry.

Tetrel Bonds between Phenyltrifluorosilane and Dimethyl Sulfoxide: Influence of Basis Sets, Substitution and Competition

Ab initio calculations have been performed for the complexes of DMSO and phenyltrifluorosilane (PTS) and its derivatives with a substituent of NH₃, OCH₃, CH₃, OH, F, CHO, CN, NO₂, and SO₃H. It is necessary to use sufficiently flexible basis sets, such as aug’-cc-pVTZ, to get reliable results for the Si···O tetrel bonds. The tetrel bond in these complexes has been characterized in views of geometries, interaction energies, orbital interactions and topological parameters. The electron-donating group in PTS weakens this interaction and the electron-withdrawing group prominently strengthens it to the point where it exceeds that of the majority of hydrogen bonds. The largest interaction energy occurs in the p-HO₃S-PhSiF₃···DMSO complex, amounting to −122 kJ/mol. The strong Si···O tetrel bond depends to a large extent on the charge transfer from the O lone pair into the empty p orbital of Si, although it has a dominant electrostatic character. For the PTS derivatives of NH₂, OH, CHO and NO₂, the hydrogen bonded complex is favorable to the tetrel bonded complex for the NH₂ and OH derivatives, while the σ-hole interaction prefers the π-hole interaction for the CHO and NO₂ derivatives.

Origins and properties of the tetrel bond

The tetrel bond (TB) recruits an element drawn from the C, Si, Ge, Sn, Pb family as electron acceptor in an interaction with a partner Lewis base. The underlying principles that explain this attractive interaction are described in terms of occupied and vacant orbitals, total electron density, and electrostatic potential. These principles facilitate a delineation of the factors that feed into a strong TB. The geometric deformation that occurs within the tetrel-bearing Lewis acid monomer is a particularly important issue, with both primary and secondary effects. As a first-row atom of low polarizability, C is a reluctant participant in TBs, but its preponderance in organic and biochemistry make it extremely important that its potential in this regard be thoroughly understood. The IR and NMR manifestations of tetrel bonding are explored as spectroscopy offers a bridge to experimental examination of this phenomenon. In addition to the most common σ-hole type TBs, discussion is provided of π-hole interactions which are a result of a common alternate covalent bonding pattern of tetrel atoms.

Strengthening of halogen bond in XCl∙∙∙FH∙∙∙F- through cooperativity with a strong hydrogen bond and proton transfer

A theoretical calculation has been performed for the ternary complexes XCl∙∙∙FH∙∙∙F^- (X = CCH, CN, OH, NC, and F) and the corresponding binary complexes. The halogen bond in the dyad is very weak with the interaction energy less than 2.5 kcal/mol. Interestingly, the halogen bond gets a big enhancement when it combines with a very strong hydrogen bond in FH∙∙∙F^-, and the largest interaction energy is up to ∼25.6 kcal/mol in FCl∙∙∙FH∙∙∙F^-. The enhancement of halogen bond not only results in a larger elongation of X-Cl bond and a bigger redshift of the bond stretch vibration but also makes the blue-shifting halogen bond in NCCl∙∙∙FH be a red-shifting one in NCCl∙∙∙FH∙∙∙F^-. The halogen bond belongs to a purely close-shell interaction in the dyad, while it becomes a partially covalent interaction in XCl∙∙∙FH∙∙∙F^- (X = OH, NC, and F) with negative energy density. In FH∙∙∙F^-, the proton is shared between the two F atoms, however, this proton transfers towards the F^- end in XCl∙∙∙FH∙∙∙F^-.

Comparison of tetrel bonds in neutral and protonated complexes of pyridineTF3and furanTF3(T = C, Si, and Ge) with NH3

Protonation not only changes the primary interaction mode between α/β-furanCF₃/p-PyCF₃and NH₃but also prominently enhances the strength of the Si/Ge⋯N tetrel bond.

Modulating the strength of tetrel bonding through beryllium bonding

Quantum chemical calculations were performed to investigate the stability of the ternary complexes BeH2···XMH3···NH3 (X = F, Cl, and Br; M = C, Si, and Ge) and the corresponding binary complexes at the atomic level. Our results reveal that the stability of the XMH3···BeH2 complexes is mainly due to both a strong beryllium bond and a weak tetrel-hydride interaction, while the XMH3···NH3 complexes are stabilized by a tetrel bond. The beryllium bond with a halogen atom as the electron donor has many features in common with a beryllium bond with an O or N atom as the electron donor, although they do exhibit some different characteristics. The stability of the XMH3···NH3 complex is dominated by the electrostatic interaction, while the orbital interaction also makes an important contribution. Interestingly, as the identities of the X and M atoms are varied, the strength of the tetrel bond fluctuates in an irregular manner, which can explained by changes in electrostatic potentials and orbital interactions. In the ternary systems, both the beryllium bond and the tetrel bond are enhanced, which is mainly ascribed to increased electrostatic potentials on the corresponding atoms and charge transfer. In particular, when compared to the strengths of the tetrel and beryllium bonds in the binary systems, in the ternary systems the tetrel bond is enhanced to a greater degree than the beryllium bond. Graphical Abstract A tetrel bond can be strengthened greatly by a beryllium bond.