Abstract
Molecules of the type XYT = Ch (T = C, Si, Ge; Ch = S, Se; X,Y = H, CH3, Cl, Br, I) contain a σ-hole along the T = Ch bond extension. This hole can engage with the N lone pair of NCH and NCCH3 so as to form a chalcogen bond. In the case of T = C, these bonds are rather weak, less than 3 kcal/mol, and are slightly weakened in acetone or water. They owe their stability to attractive electrostatic energy, supplemented by dispersion, and a much smaller polarization term. Immersion in solvent reverses the electrostatic interaction to repulsive, while amplifying the polarization energy. The σ-holes are smaller for T = Si and Ge, even negative in many cases. These Lewis acids can nonetheless engage in a weak chalcogen bond. This bond owes its stability to dispersion in the gas phase, but it is polarization that dominates in solution.
Highlights
The venerable Lewis theory of acids and bases is the foundation for understanding the nature of noncovalent interactions between molecules
Since the Gaussian software package does not allow the use of this method in conjunction with the polarizable continuum model (PCM) solvent model, the correction calculated for the solvent geometry in the gas phase was used
Many molecules in the XYT=Ch series can engage in a chalcogen bond with the Nbases NCH and NCMe
Summary
The venerable Lewis theory of acids and bases is the foundation for understanding the nature of noncovalent interactions between molecules. Interactions based on the charge transfer between interacting molecules are the essence of common and important interactions in both biological and chemical areas Such interactions are the domain of the elements of the main groups of the periodic table. The bonding terms triel (Group 13), tetrel [1,2,3] (Group 14), pnicogen [4,5] (Group 15), chalcogen [6,7] (Group 16), halogen [8,9] (Group 17), or aerogen (noble gas) atoms (Group 18) are used for elements that act as Lewis acids. Consistent with this, as for the H bond [13], halogen [14] and chalcogen [15] bonds, their origins and properties, have been formally defined by IUPAC
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