Self-assembly of a trigonal bipyramidal architecture with stabilisation of iron in three spin states

Self-assembly and characterisation of a supramolecular trigonal bipyramidal iron cage containing an [Fe-III(mu(2)-F)(6)(Fe-II)(3)](3+) star motif at its core is reported. The complex can be formed in a one step reaction using an heterotopic ligand that supports site-specific incorporation of iron in three distinct electronic configurations: low-spin Fe-II, high-spin Fe-II and high-spin Fe-III, with iron(ii) tetrafluoroborate as the source of the bridging fluorides. Formation of a mu(2)-F bridged mixed-valence Fe-II-Fe-III star is unprecedented. The peripheral high-spin Fe-II centres of the mixed-valence tetranuclear star incorporated in the iron cage are highly anisotropic and engage in F-mediated antiferromagnetic exchange with the central Fe-III ion.