An octahedral coordination cage with six Fe(III) centers as a MRI probe.

The incorporation of multiple Fe(III) centers bridged by rigid ligands into a coordination cage represents a powerful approach for designing effective MRI contrast agents. In this context, an octahedral coordination cage with six high-spin Fe(III) centers is shown to be water soluble, robust towards dissociation and has effective relaxivity as a MRI probe in solution and in mice.