The σ and π Holes. The Halogen and Tetrel Bondings: Their Nature, Importance and Chemical, Biological and Medicinal Implications

Abstract

The non-covalent halogen bonding, or simply halogen bonding, is known since last century and it was slightly explored by several scientists in the fifties. However, the scientific community started to recognize the importance and applications of the halogen bonding in the last two decades. Now, great efforts are being done on theoretical studies to better understand the fundamental backgrounds of this type of bonding and, also, on the study of the potential of these interactions and their applications in a wide variety of areas, like materials science, biomedicine or drug design and optimization. Moreover, it is possible to find applications in organic synthesis, organocatalysis, and also in the study of the stereochemistry and conformational stability of halogenated biomolecules. This phenomenon, observed for the halogen atoms, is now also appreciated in other elements of the right side of the periodic table, like for example the tetrels, the pnicogens, the chalcogens and even the noble gases or aerogens. In this review article, the perspectives of these non-covalent bonds are analysed, especially for the case of halogen atoms and tetrels, putting emphasis in their potential and their actual and future applications. This review does not pretend to be a deep and extensive revision but to give a perspective of this type of bonding, with the aim of being informative and understandable, and also stimulant for non-experts in this matter.