Reaching into the non-covalent toolbox

Electrophilic halogens became a key part of the broader concept of halogen bonding, a term first used in 1961. This is somewhat like hydrogen bonding, another common form of vital non-covalent attraction. In hydrogen bonding, electrophilic hydrogen atoms bonded to electron-withdrawing atoms are attracted to electron-rich atoms like oxygen and nitrogen. In halogen bonding, electrophilic regions of halogen atoms are likewise attracted to electron-rich atoms.

In the last few years, similar concepts have emerged where atoms from group 16 of the periodic table are the electrophile, known as chalcogenide bonds. Analogous interactions exist with group 15 electrophiles, known as pnictogen bonds, and with group 14 atoms, known as tetrel bonds. Another relatively exotic idea is that of weak hydrogen bonding, where the hydrogen atom is relatively weakly electrophilic, because the atom it’s bonded to is less electron-withdrawing, like carbon, for example.

Today, these and other recently discovered forms of non-covalent bonding certainly help provide better answers to how molecules crystallise. Non-covalent bonding types new and old drive applications spanning the entirety of chemistry, from liquid crystal displays (LCDs) to dynamic medical therapies and sensors for biological processes. Bringing different types of non-covalent bonding together can also create subtle and intricate chemical systems.