Resolution of the σ-hole Anisotropic distribution of charges on atoms plays an important role in intermolecular interactions, yet direct experimental imaging remains a long-standing challenge. A good example is the σ-hole, an anisotropic charge distribution on a halogen atom covalently linked to carbon atoms. The σ-hole gives rise to the halogen-bonding mechanism, which is well known in supramolecular chemistry despite its existence being confirmed only indirectly. Mallada et al . developed Kelvin probe force microscopy with a specifically functionalized tip and report direct real-space visualization of the σ-hole, revealing its strong anisotropic charge distribution. The authors show that this technique, which relies entirely on electrostatic interactions, may be a powerful tool with which to study anisotropic atomic charge distributions. —YS

It is generally expected that a solvent has only marginal effect on the stability of a covalent bond. In this work, we present a combined computational and experimental study showing a surprising stabilization of the covalent/dative bond in Me3NBH3 complex with increasing solvent polarity. The results show that for a given complex, its stability correlates with the strength of the bond. Notably, the trends in calculated changes of binding (free) energies, observed with increasing solvent polarity, match the differences in the solvation energies (ΔEsolv) of the complex and isolated fragments. Furthermore, the studies performed on the set of the dative complexes, with different atoms involved in the bond, show a linear correlation between the changes of binding free energies and ΔEsolv. The observed data indicate that the ionic part of the combined ionic-covalent character of the bond is responsible for the stabilizing effects of solvents.

The complexes formed between carbon allotropes (C 20 ,C 60 fullerenes,g raphene,a nd single-wall carbon nanotubes) and piperidine have been investigated by means of computational quantum chemical and experimental IR and NMR techniques.A longside hydrogen bonds,t he C•••N tetrel bond, and lone-pair•••p interactions,t he unexpected N!C dative/covalent bond has been detected solely in complexes of fullerenes with piperidine.N on-planarity and five-member rings of carbon allotropes represent the key structural prerequisites for the unique formation of ad ative N!Cb ond. The results of thermodynamics calculations,m olecular dynamics simulations,a nd NMR and FTIR spectroscopye xplain the specific interactions between C 60 and piperidine.T he differences in behavior of individual carbon allotropes in terms of dative bonding formation brings an ew insight into their controllable organic functionalization. Scheme 1. Fullerenes C 20 and C 60 and pip (C 5 H 11 N).