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1. Anion–anion and anion–neutral triel bonds

   https://doi.org/10.1039/D0CP06547A  

   Wysokiński, Rafał ; Michalczyk, Mariusz ; Zierkiewicz, Wiktor ; Scheiner, Steve ( March 2021 , Physical Chemistry Chemical Physics)

   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. 

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2. Ability of Lewis Acids with Shallow σ-Holes to Engage in Chalcogen Bonds in Different Environments

   https://doi.org/10.3390/molecules26216394  

   Wysokiński, Rafał ; Zierkiewicz, Wiktor ; Michalczyk, Mariusz ; Scheiner, Steve ( November 2021 , Molecules)

   Molecules of the type XYT = Ch (T = C, Si, Ge; Ch = S, Se; X,Y = H, CH3, Cl, Br, I) contain a σ-hole along the T = Ch bond extension. This hole can engage with the N lone pair of NCH and NCCH3 so as to form a chalcogen bond. In the case of T = C, these bonds are rather weak, less than 3 kcal/mol, and are slightly weakened in acetone or water. They owe their stability to attractive electrostatic energy, supplemented by dispersion, and a much smaller polarization term. Immersion in solvent reverses the electrostatic interaction to repulsive, while amplifying the polarization energy. The σ-holes are smaller for T = Si and Ge, even negative in many cases. These Lewis acids can nonetheless engage in a weak chalcogen bond. This bond owes its stability to dispersion in the gas phase, but it is polarization that dominates in solution. 

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3. Weak σ‐Hole Triel Bond between C 5 H 5 Tr (Tr=B, Al, Ga) and Haloethyne: Substituent and Cooperativity Effects

   https://doi.org/10.1002/cphc.202000955  

   Yang, Qingqing ; Zhou, Bohua ; Li, Qingzhong ; Scheiner, Steve ( February 2021 , ChemPhysChem)

   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.

    

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4. Origins and properties of the tetrel bond

   https://doi.org/10.1039/D1CP00242B  

   Scheiner, Steve ( March 2021 , Physical Chemistry Chemical Physics)

   null (Ed.)

   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. 

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5. Noncovalent bond between tetrel π-hole and hydride

   https://doi.org/10.1039/D1CP01245B  

   Liu, Na ; Liu, Jiaxing ; Li, Qingzhong ; Scheiner, Steve ( May 2021 , Physical Chemistry Chemical Physics)

   The π-hole above the plane of the X 2 T′Y molecule (T′ = Si, Ge, Sn; X = F, Cl, H; Y = O, S) was allowed to interact with the TH hydride of TH(CH 3 ) 3 (T = Si, Ge, Sn). The resulting TH⋯T′ tetrel bond is quite strong, with interaction energies exceeding 30 kcal mol −1 . F 2 T′O engages in the strongest such bonds, as compared to F 2 T′S, Cl 2 T′O, or Cl 2 T′S. The bond weakens as T′ grows larger as in Si > Ge > Sn, despite the opposite trend in the depth of the π-hole. The reverse pattern of stronger tetrel bond with larger T is observed for the Lewis base TH(CH 3 ) 3 , even though the minimum in the electrostatic potential around the H is nearly independent of T. The TH⋯T′ arrangement is nonlinear which can be understood on the basis of the positions of the extrema in the molecular electrostatic potentials of the monomers. The tetrel bond is weakened when H 2 O forms an O⋯T′ tetrel bond with the second π-hole of F 2 T′O, and strengthened if H 2 O participates in an OH⋯O H-bond. 

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