skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: Triel bonds within anion ··· anion complexes
The ability of two anions to interact with one another is tested in the context of pairs of TrX 4 − homodimers, where Tr represents any of the triel atoms B, Al, Ga, In, or Tl, and X refers to a halogen substituent F, Cl, or Br. None of these pairs engage in a stable complex in the gas phase, but the situation reverses in water where the two monomers are held together by Tr⋯X triel bonds, complemented by stabilizing interactions between X atoms. Some of these bonds are quite strong, notably those involving TrF 4 − , with interaction energies surpassing 30 kcal mol −1 . Others are very much weaker, with scarcely exothermic binding energies. The highly repulsive electrostatic interactions are counteracted by large polarization energies.  more » « less
Award ID(s):
1954310
PAR ID:
10326173
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Physical Chemistry Chemical Physics
Volume:
23
Issue:
44
ISSN:
1463-9076
Page Range / eLocation ID:
25097 to 25106
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    The ability of a TrCl 4 − anion (Tr = Al, Ga, In, Tl) to engage in a triel bond with both a neutral NH 3 and CN − anion is assessed by ab initio quantum calculations in both the gas phase and in aqueous medium. Despite the absence of a positive σ or π-hole on the Lewis acid, strong triel bonds can be formed with either base. The complexation involves an internal restructuring of the tetrahedral TrCl 4 − monomer into a trigonal bipyramid shape, where the base can occupy either an axial or equatorial position. Although this rearrangement requires a substantial investment of energy, it aids the complexation by imparting a much more positive MEP to the site that is to be occupied by the base. Complexation with the neutral base is exothermic in the gas phase and even more so in water where interaction energies can exceed 30 kcal mol −1 . Despite the long-range coulombic repulsion between any pair of anions, CN − can also engage in a strong triel bond with TrCl 4 − . In the gas phase, complexation is endothermic, but dissociation of the metastable dimer is obstructed by an energy barrier. The situation is entirely different in solution, with large negative interaction energies of as much as −50 kcal mol −1 . The complexation remains an exothermic process even after the large monomer deformation energy is factored in. 
    more » « less
  2. Abstract The replacement of a CH group of benzene by a triel (Tr) atom places a positive region of electrostatic potential near the Tr atom in the plane of the aromatic ring. This σ‐hole can interact with an X lone pair of XCCH (X=F, Cl, Br, and I) to form a triel bond (TrB). The interaction energy between C5H5Tr and FCCH lies in the range between 2.2 and 4.4 kcal/mol, in the order Tr=B+cation above the ring pulls density toward itself and thus magnifies the Tr σ‐hole. The TrB to the XCCH nucleophile is thereby magnified as is the strength of the TrB. This positive cooperativity is particularly large for Tr=B. 
    more » « less
  3. Abstract The triel bond (TrB) formed between Be(CH3)2/Mg(CH3)2and TrX3(Tr=B, Al, and Ga; X=H, F, Cl, Br, and I) is investigated via the MP2/aug‐cc‐pVTZ(PP) quantum chemical protocol. The C atoms of the methyl groups in M(CH3)2are characterized by a negative electrostatic potential and act as an electron donor in a triel bond with the π‐hole above the Tr atom of planar TrX3. The interaction energy spans a wide range between −2 and −69 kcal/mol. Mg(CH3)2forms a stronger TrB than does Be(CH3)2, which comports with the more negative electrostatic potential on its methyl groups. Some of the complexes involving Mg display a high degree of transfer of the methyl group from Mg to Tr, which is accompanied by an inversion of the bridging methyl and a sizable pyramidalization of the TrX3unit. The geometries of these complexes have the properties of the long sought pentacoordinate C which has eluded identification and characterization in the past. 
    more » « less
  4. The possibility that MX 3 − anions can interact with one another is assessed via ab initio calculations in gas phase as well as in aqueous and ethanol solution. A pair of such anions can engage in two different dimer types. In the bridged configuration, two X atoms engage with two M atoms in a rhomboid structure with four equal M–X bond lengths. The two monomers retain their identity in the stacked geometry which contains a pair of noncovalent M⋯X interactions. The relative stabilities of these two structures depend on the nature of the central M atom, the halogen substituent, and the presence of solvent. The interaction and binding energies are fairly small, generally no more than 10 kcal mol −1 . The large electrostatic repulsion is balanced by a strong attractive polarization energy. 
    more » « less
  5. The possibility that the intramolecular Tr⋯S triel bond is strengthened by resonance is examined by quantum chemical calculations within the planar five-membered ring of TrH 2 –CRCR–CRS (Tr = Al, Ga, In; R = NO 2 , CH 3 ). This internal bond is found to be rather short (2.4–2.7 Å) with a large bond energy between 12 and 21 kcal mol −1 . The pattern of bond length alternation and atomic charges within the ring is consistent with resonance involving the conjugated double bonds. This resonance enhances the triel bond strength by some 25%. The electron-withdrawing NO 2 group weakens the bond, but it is strengthened by the electron-donating CH 3 substituent. NICS analysis suggests the presence of a certain degree of aromaticity within the ring. 
    more » « less