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 [FeIII(μ2-F)6(FeII)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 FeII, high-spin FeII and high-spin FeIII, with iron(II) tetrafluoroborate as the source of the bridging fluorides. Formation of a μ2-F bridged mixed-valence FeII-FeIII star is unprecedented. The peripheral high-spin FeII 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 FeIII ion.