Coordination clusters as emerging magnetic resonance imaging contrast agents

Magnetic resonance imaging (MRI) has become an indispensable diagnostic modality in clinical medicine owing to its superior spatial resolution and deep tissue penetration, particularly when contrast agents are exploited. Current clinical protocols predominantly utilize mononuclear gadolinium(III) complexes as contrast agents. Recently, coordination clusters composed of multi-nuclear paramagnetic metal ions (such as Gd 3+ , Mn 2+ , and Fe 3+ ) have demonstrated promisingly higher relaxation rates as MRI contrast agents and adaptable stability in various solutions, offering promising medical application prospects. This minireview mainly highlights such advancements, focusing on the influence of ligand selection and structural design on the relaxation rates of metal clusters as MRI contrast agents.