An official website of the United States government
When attached to a tetrazole, a TtR 3 group (Tt = C, Si; R = H, F) engages in a Tt⋯N tetrel bond (TtB) with the Lewis base NCM (M = Li, Na). MP2/aug-cc-pVTZ calculations find that the Si⋯N TtB is rather strong, more than 20 kcal mol −1 for SiH 3 , and between 46 and 53 kcal mol −1 for SiF 3 . The C⋯N TtBs are relatively weaker, less than 8 kcal mol −1 . All of these bonds are intensified when a BH 3 or BF 3 molecule forms a triel bond to a N atom of the tetrazole ring, particularly for the C⋯N TtB, up to 11 kcal mol −1 . In these triads, the SiR 3 group displaces far enough along the line toward the base that it may be thought of as half transferred.
more »
« less
Diboron Bonds Between BX 3 (X=H, F, CH 3 ) and BYZ 2 (Y=H, F; Z=CO, N 2 , CNH)
Abstract The ability of B atoms on two different molecules to engage with one another in a noncovalent diboron bond is studied by ab initio calculations. Due to electron donation from its substituents, the trivalent B atom of BYZ2(Z=CO, N2, and CNH; Y=H and F) has the ability to in turn donate charge to the B of a BX3molecule (X=H, F, and CH3), thus forming a B⋅⋅⋅B diboron bond. These bonds are of two different strengths and character. BH(CO)2and BH(CNH)2, and their fluorosubstituted analogues BF(CO)2and BF(CNH)2, engage in a typical noncovalent bond with B(CH3)3and BF3, with interaction energies in the 3–8 kcal/mol range. Certain other combinations result in a much stronger diboron bond, in the 26–44 kcal/mol range, and with a high degree of covalent character. Bonds of this type occur when BH3is added to BH(CO)2, BH(CNH)2, BH(N2)2, and BF(CO)2, or in the complexes of BH(N2)2with B(CH3)3and BF3. The weaker noncovalent bonds are held together by roughly equal electrostatic and dispersion components, complemented by smaller polarization energy, while polarization is primarily responsible for the stronger ones.
more »
« less
- Award ID(s):
- 1954310
- PAR ID:
- 10250175
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 22
- Issue:
- 14
- ISSN:
- 1439-4235
- Format(s):
- Medium: X Size: p. 1461-1469
- Size(s):
- p. 1461-1469
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
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
-
Abstract The starting point for this work was a set of crystal structures containing the motif of interaction between methyl groups in homodimers. Two structures were selected for which QTAIM, NCI and NBO analyses suggested an attractive interaction. However, the calculated interaction energy was negative for only one of these systems. The ability of methyl groups to interact with one another is then examined by DFT calculations. A series of (CH3PnHCH3)2homodimers were allowed to interact with each other for a range of Pn atoms N, P, As, and Sb. Interaction energies of these C⋅⋅⋅C tetrel‐bonded species were below 1 kcal/mol, but could be raised to nearly 3 kcal/mol if the C atom was changed to a heavier tetrel. A strengthening of the C⋅⋅⋅C intermethyl bonds can also be achieved by introducing an asymmetry via an electron‐withdrawing substituent on one unit and a donor on the other. The attractions between the methyl and related groups occur in spite of a coulombic repulsion between σ‐holes on the two groups. NBO, AIM, and NCI tools must be interpreted with caution as they can falsely suggest bonding when the potentials are repulsive.more » « less
-
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
