Cooperative effects between triel and halogen bonds in complexes of pyridine derivatives: An opposite effect of the nitrogen oxidation on triel and halogen bonds

2022

Quantum calculations study the manner in which the involvement of a halogen atom as a proton acceptor in one or more H bonds (HBs) affects the strength of the halogen bond (XB) it can form with a nucleophile aligned with the X σ-hole. A variety of Lewis acids wherein X = F, Cl, Br, and I are attached to a tetrel atom C or Ge engaged in a XB with nucleophile NH3. One, two, and three HF molecules were positioned perpendicular to the XB axis so that they could form a HB to the X atom. Each such HB strengthened the XB by an increment of 1 kcal/mol or more that does not attenuate as each new HB is added, potentially increasing the interaction energy manyfold. Additionally, the presence of one or more HBs facilitates the formation of a XB by molecules which are reluctant to engage in such a bond in the absence of these auxiliary interactions. Even the F atom, which avoids such a XB, can be coaxed to participate in a XB of moderate strength by one or more of these external HBs.

Section: Introductionsupporting

confidence: 74%

Ability of Peripheral H Bonds to Strengthen a Halogen Bond

2022

“…This sort of enhancement of the electron-accepting ability of a molecule by its interaction with another is an example of cooperativity, − which is often discussed within the context of HBs but is equally valid with respect to XBs. The overarching conclusion from previous studies of general XB cooperativity − confirms the premise that reinforcement of both bonds occurs when the central unit acts simultaneously as both electron donor and acceptor. And in particular, there are several examples demonstrating the cooperativity between a XB and a HB. − …”

Section: Introductionsupporting

confidence: 59%

Enhancement of Halogen Bond Strength by Intramolecular H-Bonds

2023

Quantum calculations study the potential of an intramolecular H-bond between the halogen atom (X) of a halobenzene and a substituent placed ortho to it, to amplify the ability of X to engage in a halogen bond (XB) with a Lewis base. H-bonding substituents NH2, CH2CH2OH, CH2OH, OH, and COOH were added to halobenzenes (X = Cl, Br, I). The amino group had little effect, but those containing OH increased the CX···N XB energy to a NH3 nucleophile by about 0.5 kcal/mol; the increment associated with COOH is larger, nearly 2 kcal/mol. These energy increments were approximately doubled if two such H-bonding substituents are present. Combining a pair of ortho COOH groups with an electron-withdrawing NO2 group in the para position has a particularly large effect, raising the XB energy by about 4 kcal/mol, which can amount to as much as a 4-fold magnification.

“…Just like H-bonds, these sister interactions are also subject to cooperativity effects. ,− It is understood that the whole can be greater or less than the sum of its parts. In particular, if the central molecule B in a A··B··C triad serves as both electron donor and acceptor, the overall binding energy of this triad will be greater than the sum of the A··B and B··C binding energies in the individual dyads, i.e., positive cooperativity.…”

Section: Introductionmentioning

confidence: 99%

Competition between a Tetrel and Halogen Bond to a Common Lewis Acid

2020

The T and X atoms of TF3X (T = C, Si, Ge, Sn; X = Cl, Br, I) can engage in a tetrel or halogen bond, respectively, with an approaching NH3 base. With the exception of T = C, the tetrel bonds are considerably stronger than the halogen bond regardless of the nature of T or X. Because both bonds involve electron acceptance by the central TF3X Lewis acid, there is a negative cooperativity between these two bonds when both are present. The halogen bond is weakened much more than is the tetrel bond and is in fact completely disrupted in some cases. Replacement of the three F substituents on TF3X by H attenuates the σ-holes on both T and X atoms, weakens and stretches both bonds, and eliminates any halogen bonds involving Cl. Even in those cases where a halogen bond does occur in the dimer, this bond cannot withstand the presence of a simultaneous tetrel bond and so disappears.