On the Importance of σ–Hole Interactions in Crystal Structures

Abstract

Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems (aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF4−, PF6−, ClO4−, etc.). Moreover, elements of groups 15 to 17 are also able to act as Lewis bases (from one to three available lone pairs, respectively), thus presenting a dual character. These emerging NCIs where the main group element behaves as Lewis base, belong to the σ–hole family of interactions. Particularly (i) tetrel bonding for elements belonging to group 14, (ii) pnictogen bonding for group 15, (iii) chalcogen bonding for group 16, (iv) halogen bonding for group 17, and (v) noble gas bondings for group 18. In general, σ–hole interactions exhibit different features when moving along the same group (offering larger and more positive σ–holes) or the same row (presenting a different number of available σ–holes and directionality) of the periodic table. This is illustrated in this review by using several examples retrieved from the Cambridge Structural Database (CSD), especially focused on σ–hole interactions, complemented with molecular electrostatic potential surfaces of model systems.

The physical nature of the ultrashort spike–ring interaction in iron maiden molecules

“…The F⋯ π interaction, however, would be anti‐bonding regardless of n . Presumably, this result can be explained qualitatively by referring to the concept of a σ ‐hole on a halogen atom 51,52 . Namely, a strongly electronegative fluorine atom with practically no σ ‐hole should interact with the π ‐electron system of the benzene ring repulsively, while the chlorine atom, and especially bromine, has a well‐marked σ ‐hole, which should interact with the π ‐electron system attractively, i.e.…”

Inorganic–organic {dz2-MIIS4}⋯π-hole stacking in reverse sandwich structures: the case of cocrystals of group 10 metal dithiocarbamates with electron-deficient arenes

“…In the past five years, the demand for square-planar d 8 -metal complexes as sterically accessible sites involved in diverse noncovalent interactions has increased dramatically. [1][2][3][4][5][6][7][8][9][10][11][12] Despite their positive charges, these centers can function as d z 2-orbital centered nucleophiles (hereinafter d z 2-nucleophiles) toward various σ-hole donors (for a recent review see ref. 13).…”

The Phosphorus Bond, or the Phosphorus-Centered Pnictogen Bond: The Covalently Bound Phosphorus Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

“…Noncovalent interactions show up in different flavors, including, for example, hydrogen bonding [ 23 ], halogen bonding [ 24 ], tetrel bonding [ 25 , 26 , 27 ], chalcogen bonding [ 28 ], pnictogen bonding [ 29 , 30 , 31 , 32 ], aerogen bonding [ 33 ], van der Waals interactions [ 34 ], and several others [ 35 ]. They are the result of attractive engagements between sites of unequal charge density and are often identified to be of Coulombic origin (a positive site attracting a negative one).…”