Noncovalent Bonds through Sigma and Pi-Hole Located on the Same Molecule. Guiding Principles and Comparisons

Abstract

Over the last years, scientific interest in noncovalent interactions based on the presence of electron-depleted regions called σ-holes or π-holes has markedly accelerated. Their high directionality and strength, comparable to hydrogen bonds, has been documented in many fields of modern chemistry. The current review gathers and digests recent results concerning these bonds, with a focus on those systems where both σ and π-holes are present on the same molecule. The underlying principles guiding the bonding in both sorts of interactions are discussed, and the trends that emerge from recent work offer a guide as to how one might design systems that allow multiple noncovalent bonds to occur simultaneously, or that prefer one bond type over another.

Keywords: chalcogen bond; cooperativity; halogen bond; molecular electrostatic potential; pnicogen bond; tetrel bond.

Figure 1

Family of σ and π-hole interactions.

Figure 2

Ge-O NBO bonding and antibonding orbitals of GeF₂O. Red and blue colors indicate opposite phase of the wave function.

Figure 3

Electron density (10⁻⁵ au) and molecular electrostatic potential (MEP) (10⁻³ au) of GeF₂O as a function of the displacement from the molecular plane θ, at a distance of 2.5 Å from the Ge atom.

Figure 4

(a) MEP on surface of GeF₂O defined as 1.5 × vdW atomic radii. Blue and red colors refer to +0.05 and −0.05 au, respectively. (b) Optimized complex of GeF₂O with NH₃ at the mp2/aug-cc-pVDZ level, with distance in Å.

Figure 5

MEP of the isolated KrOF₂ and XeOF₂ molecules on the 0.001 au contour of the electron isodensity, at the MP2/aug-cc-pVDZ level. Color ranges, in kcal/mol, are red, greater than 40, yellow; between 20 and 40, green; between 0 and 20, blue, less than 0 (negative). Selected surface critical points V_s,max (σ and π-holes) are indicated as black dots. Reproduced from Reference [132] with permission from the PCCP Owner Societies.

Figure 6

Two binding modes of XeOF₂···NCCH₃ complexes, from Reference [137].

Figure 7

Two types of the MP2/aug-cc-pVDZ optimized structures (top and side views) of complexes of NH₃ with ZF₂C₆H₅, from Reference [133].

Figure 8

Cis and Trans arrangements of two NH₃ units complexed with YF₄ via chalcogen bonds. Reproduced from Reference [135] with permission from the PCCP Owner Societies.

Figure 9

Optimized structures of NCF complexes with water stabilized by (a) σ-hole and (b) π-hole, from Reference [153].