Tuning the Competition between Hydrogen and Tetrel Bonds by a Magnesium Bond.

A computational study of the complexes formed by TF3 OH (T=C, Si, Ge) with three nitrogen-containing bases NCH, NH3 , and imidazole (IM) is carried out at the MP2/aug-cc-pVTZ level. TF3 OH can participate in two different types of noncovalent interactions: a hydrogen bond (HB) involving the hydroxyl proton and a tetrel bond (TB) with the tetel atom T. The strength of the HB is largely unaffected by the identity of T while the TB is enhanced as T grows larger. The HB is preferred over the TB for most systems, with the exception of GeF3 OH with either NH3 or IM. MgCl2 engages in a Mg⋅⋅⋅O Magnesium bond (Mg-bond) with the TF3 OH O atom, which cooperatively enhances both the HB and TB. The HB strengthening is particularly large for the NH3 or IM bases, and especially for CF3 OH, but is slowly reduced as the T atom grows larger. The TB enhancement, on the other hand, behaves in the opposite fashion, accelerating for the larger T atoms. As a bottom line, the Mg-bond generally reinforces and accentuates the preference for the HB or TB that is already present in the dimer. The Mg-bond is also responsible for a proton transfer in the HB configurations with NH3 and IM.

Comparison between Hydrogen and Halogen Bonds in Complexes of 6-OX-Fulvene with Pnicogen and Chalcogen Electron Donors.

Quantum chemical calculations are applied to complexes of 6-OX-fulvene (X=H, Cl, Br, I) with ZH3 /H2 Y (Z=N, P, As, Sb; Y=O, S, Se, Te) to study the competition between the hydrogen bond and the halogen bond. The H-bond weakens as the base atom grows in size and the associated negative electrostatic potential on the Lewis base atom diminishes. The pattern for the halogen bonds is more complicated. In most cases, the halogen bond is stronger for the heavier halogen atom, and pnicogen electron donors are more strongly bound than chalcogen. Halogen bonds to chalcogen atoms strengthen in the order O

Systematic study of the substitution effect on the tetrel bond between 1,4-diazabicyclo[2.2.2]octane and TH3X.

A tetrel bond was characterized in the complexes of 1,4-diazabicyclo[2.2.2]octane (DABCO) with TH3X (T = C, Si, Ge; X= -Me, -H, -OH, -NH2, -F, -Cl, -Br, -I, -CN, -NO2). DABCO engages in a weak tetrel bond with CH3X but a stronger one with SiH3X and GeH3X. SiH3X is favorable to bind with DABCO relative to GeH3X, inconsistent with the magnitude of the σ-hole on the tetrel atom. The methyl group in the tetrel donor weakens the tetrel bond but an enhancing effect is found for the other substituents, particularly -NO2. The substitution effect is also related to the nature of the tetrel atom. The halogen substitution from F to I has a weakening effect in the CH3X complex but an enhancing effect in the SiH3X complex and a negligible effect in the GeH3X complex. The above abnormal results found in these complexes can be partly attributed to the charge transfer from the lone pair on the nitrogen atom of DABCO into the anti-bonding orbital σ*(T-X) of TH3X. The stability of both SiH3X and GeH3X complexes is primarily controlled by electrostatic interactions and polarization.

Tetrel Bond between 6-OTX3-Fulvene and NH3: Substituents and Aromaticity.

Carbon bonding is a weak interaction, particularly when a neutral molecule acts as an electron donor. Thus, there is an interesting question of how to enhance carbon bonding. In this paper, we found that the ⁻OCH3 group at the exocyclic carbon of fulvene can form a moderate carbon bond with NH3 with an interaction energy of about -10 kJ/mol. The ⁻OSiH3 group engages in a stronger tetrel bond than does the ⁻OGeH3 group, while a reverse result is found for both ⁻OSiF3 and ⁻OGeF3 groups. The abnormal order in the former is mainly due to the stronger orbital interaction in the ⁻OSiH3 complex, which has a larger deformation energy. The cyano groups adjoined to the fulvene ring not only cause a change in the interaction type, from vdW interactions in the unsubstituted system of ⁻OCF3 to carbon bonding, but also greatly strengthen tetrel bonding. The formation of tetrel bonding has an enhancing effect on the aromaticity of the fulvene ring.