Topic overview

Start with the big picture

As nuclear charge increases across the lanthanoid series, poorly shielding 4f electrons contribute to a steady decrease in ionic radius, known as the lanthanoid contraction. The resulting high charge density helps explain lanthanoids’ affinity for oxygen- and fluoride-containing ligands, as well as their preference for high coordination numbers and stable chelate formation. Their unpaired 4f electrons can produce paramagnetism, while characteristic f–f transitions support luminescent probes. In clinical contexts, these features relate to gadolinium-based MRI agents and therapeutic or theranostic radiolanthanoids. Understanding solubility, hydrolysis, chelation, and toxicity is also important: intact chelation helps limit precipitation and the risks associated with free gadolinium ions.