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Strong negative charge on the tetravalent apical C of propellane can attract an electrophile, which can then extract charge from the prominent lobe of its C–C bonding orbital, to form a strong noncovalent bond with C as an electron donor. 

The occurrence of these anion⋯anion dimers in the crystal structure are dependent on the presence of counterions as the attraction between two Au(iii) centers is insufficient to override the coulombic repulsion. 

Inert noble gas atoms are engaged in different forms of halonium cations. Attractive X⋯Ng interactions can vary widely in strength from 1 even up to 25 kcal mol⁻¹. 

The wolfium bond is a recently described noncovalent interaction in which metals belonging to group 6 act as electron acceptors. 

In the investigated complexes, the metal atom acts as a Lewis base, with the occupied d_z²orbital serving as the source of charge transferred to the Lewis acid. 

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. 

The halogen bond formed by a series of Lewis acids TF 3 X (T = C, Si, Ge, Sn, Pb; X = Cl, Br, I) with NH 3 is studied by quantum chemical calculations. The interaction energy is closely mimicked by the depth of the σ-hole on the X atom as well as the full electrostatic energy. There is a first trend by which the hole is deepened if the T atom to which X is attached becomes more electron-withdrawing: C > Si > Ge > Sn > Pb. On the other hand, larger more polarizable T atoms are better able to transmit the electron-withdrawing power of the F substituents. The combination of these two opposing factors leaves PbF 3 X forming the strongest XBs, followed by CF 3 X, with SiF 3 X engaging in the weakest bonds. The charge transfer from the NH 3 lone pair into the σ*(TX) antibonding orbital tends to elongate the covalent TX bond, and this force is largest for the heavier X and T atoms. On the other hand, the contraction of this bond deepens the σ-hole at the X atom, which would enhance both the electrostatic component and the full interaction energy. This bond-shortening effect is greatest for the lighter X atoms. The combination of these two opposing forces leaves the T–X bond contracting for X = Cl and Br, but lengthening for I.