π-Hole spodium bonding in tri-coordinated Hg(ii) complexes

The important role of pi-hole spodium bonding in tri-coordinated planar Hg(ii) complexes is highlighted in this feature article. Selected examples of Hg(ii)X₃ structures (X = any atom) illustrate that this noncovalent interaction is relevant as a structural guiding force in crystal structures. For some examples, the interactions have been characterized using the quantum theory of "atoms in molecules" and the noncovalent interaction plot index. Finally, an analysis of the Cambridge structural database revealed that the HgX₃ structures are predominantly T-shaped and that they are directional pi-hole donors for electron rich atoms.