Rare Earth Coordination Chemistry in Action: Exploring the Optical and Magnetic Properties of the Lanthanides in Bioscience While Challenging Current Theories

In the 1980s, developments in healthcare led to the introduction of gadolinium complexes as contrast agents for magnetic resonance imaging and targeted radiotherapeutic agents, using isotopes such as ⁹⁰Y. In each case, new rare earth coordination chemistry developed, guided by certain ligand design criteria, to provide kinetically stable systems that resisted premature metal dissociation in vivo. The paramagnetic lanthanide(III) ions have found numerous applications in analysis, imaging science, and the biosciences, notably in magnetic resonance based on fast relaxation processes and large dipolar shifts, and in diverse optical phenomena, associated with the sharp emission spectra and long-lived lifetimes characterizing the parity-forbidden f–f transitions. The theories that were developed to rationalize these experimental phenomena have limitations that preclude their widespread use; a unifying theory of electromagnetic anisotropy is required to aid the future design of functional coordination complexes, enabling realistic structure/property predictions.