Hole interactions are known by different names depending on their key atom (e.g.halogen, chalcogen, triel or hydrogen bonds), and the geometry of the interaction (σ, π, δ). Maybe we can make some order by analysing their molecular orbitals?

In this study, the nature and characteristics of a short Br...π interaction observed in an ebselen derivative, 2-(2-bromophenyl)benzo[d][1,2]selenazol-3(2H)-one, has been explored. The electronic nature of this Br...π interaction was investigated via high-resolution X-ray diffraction and periodic density functional theory calculations using atoms-in-molecules (AIM) analysis. This study unravels the simultaneous presence of σ-hole and π-hole bonding characteristics in the same interaction. The dual characteristics of this unique Br...π interaction are further established via molecular electrostatic potentials (MESPs) and natural bond orbitals (NBOs).

The nature and characteristics of the intermolecular OC⋯OC π-hole tetrel bond in the solid state have been explored and the driving force for tetrel bond formation is the electrostatically driven π-hole interaction between the most electropositive carbon atom of the carbonyl group and the most electronegative oxygen atom in the crystal. NBO calculations establish the n → π* orbital interaction present and CSD analysis quantitatively establishes the Bürgi–Dunitz angle to be ∼97.7° driven via tetrel bond formation.

In this study, we have performed a detailed analysis of the nature and strength of different intermolecular interactions present in the crystal structures of four biologically active derivatives of 1,3,4-oxadiazol-2(3H)-thiones. The study was primarily focused on obtaining detailed physical insights into the differential nature of the σ-hole and π-hole interactions that exist in the solid state in this class of compounds. It is found that the directionality of an interaction plays a very important role in categorizing these interactions as being σ-hole and π-hole in origin. The presence of a σ-hole (on the S, Cl and Br atoms) and π-holes (in the oxadiazole and benzyl rings) is clearly evident from the molecular electrostatic potential maps. The presence of these ubiquitous interactions was further confirmed via QTAIM analysis by the presence of (3, −1) bond critical points (bcps) between the interacting atoms with acceptable topological parameters (ρ_bcp; ∇²ρ_bcp). Furthermore, Hirshfeld 2D fingerprint plots helped in quantitatively determining the role of different interactions in the crystal packing of the four reported structures.

We report the mechanochemical synthesis of five single-crystalline phenylboroxine and 1,4-diazabicyclo[2.2.2]octane (DABCO) ligand-based adducts, directed by boron–nitrogen dative bonds. By tuning the electronic features of the phenylboroxines by chemical modifications (–H/–OMe/–F/–Cl/–Br) at the para-position, the formation of the resulting bicomponent adducts can be controlled to obtain molecular to 1D polymeric crystalline materials. The electrostatic and quantum topological aspects of the B←N bonds reveal the origin for the different binding modes of the boroxine–DABCO adducts yielding molecular to polymeric structures.