The synthesis of polynuclear clusters with control over size and cluster geometry remains an unsolved challenge. Herein, we report the synthesis and characterization of open-shell octairon clusters subtended by two heptaamine ligands, trenLH9. The molecular crystal structure of the all-ferrous species (trenL)2Fe8(PMe2Ph)2 (1) displays a bicapped-octahedral geometry with Fe–Fe distances ranging from 2.4071(6) to 2.8236(5) Å, where the ligand amine units are formally in amine, amide, and imide oxidation states. Several redox states of the octairon cluster are accessible as ascertained via cyclic voltammetry. The one-electron reduced clusters [M]+[(trenL)2Fe8(PMe2Ph)2]− (M = Bu4N 2a, (15-crown-5)Na(THF) 2b) were isolated and fully characterized. Variable-temperature magnetic susceptibility data indicates that the overall interaction within the [Fe8] core is antiferromagnetic (AF) and magnetometry reveals an S = 2 spin ground state and a Curie constant (θ) of −204.3. The intracore AF coupling decreases substantially in the mixed valence compound 2a (θ = −61.7). The synthetic methodology reported here could be employed to build even larger clusters.

The synthesis of polynuclear clusters with control over sizeand cluster geometry remains an unsolved challenge. Herein, we report the synthesis and characterization of openshell octairon clusters supported by two heptaamine ligands [o-H 2 NC 6 H 4 NH(CH 2 ) 2 ] 3 N( tren LH 9 ). The crystal structure of the all-ferrous species ([ tren L) 2 Fe 8 (PMe 2 Ph) 2 ]( 1)d isplays abicapped octahedral geometry with Fe À Fe distances ranging from 2.4071 (6) to 2.8236(5) , where the ligand amine units are formally in amine,a mide,a nd imide oxidation states. Several redox states of the octairon cluster are accessible,a s ascertained using cyclic voltammetry.T he one-electron-reduced clusters [M] + [( tren L) 2 Fe 8 (PMe 2 Ph) 2 ] À (M = Bu 4 N( 2a);(15-crown-5)Na(thf) (2b)) were isolated and characterized. Variable-temperature magnetic susceptibility data indicates that the exchange coupling within the [Fe 8 ]c ore is antiferromagnetic which is attenuated upon reduction to the mixed valent anion.Scheme 1. Synthesis of [( tren L) 2 Fe 8 (PMe 2 Ph) 2 ]a nd its anion. Py =pyridine.