Synthesis of Well-Defined Bicapped Octahedral Iron Clusters [(trenL)2Fe8(PMe2Ph)2]n (n=0, −1)

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 supported by two heptaamine ligands [o‐H2NC6H4NH(CH2)2]3N (trenLH9). The 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 using cyclic voltammetry. The one‐electron‐reduced clusters [M]+[(trenL)2Fe8(PMe2Ph)2]− (M=Bu4N (2 a); (15‐crown‐5)Na(thf) (2 b)) were isolated and characterized. Variable‐temperature magnetic susceptibility data indicates that the exchange coupling within the [Fe8] core is antiferromagnetic which is attenuated upon reduction to the mixed valent anion. Expanding the nuclearity: Octairon clusters with a bicapped octahedral cluster core employing a polynucleating heptaamine ligand have been synthesized and isolated. This cluster core geometry is unprecedented for first‐row transition metals. The design principles used to obtain these clusters may be extended to other transition metals or generalized to synthesize even larger clusters. Atom colors: Fe=orange; N=blue; P=purple; C=gray.