Metallacrowns: an ideal platform for accessing lanthanide luminescence

Metallacrowns (MCs) are a distinctive class of metallamacrocycles that serve as inorganic counterparts to the well-known crown ethers, in which the characteristic –[C–O–O]– repeating units are replaced by –[M–N–O]– motifs. Much like their organic analogues, the donor oxygen atoms within the MC framework can capture cations in the central cavity. The modifiable nature of MCs provides remarkable structural diversity, as both ring-forming ligands and metal ions can be varied to tune and modify the chemical and physical properties of corresponding MC. In this minireview, we focus specifically on metallacrowns bearing gallium(III) as the ring metal, highlighting their structural versatility as well as the properties and applications of Ga III -Ln III heterometallic MCs. We begin by introducing the first Ga III -based MC and trace the structural evolution of this family of MCs toward systems incorporating Ln III ions with intriguing photophysical properties that open avenues for diverse functional and applied uses.