Ligand Field Strength Mediates Electron Delocalization in Octahedral [(HL)2Fe6(L′) m ] n+ Clusters

To assess the impact of terminal ligand binding on a variety of cluster properties (redox delocalization, ground-state stabilization, and breadth of redox state accessibility), we prepared three electron-transfer series based on the hexanuclear iron cluster [(HL)2Fe6(L′) m ] n+ in which the terminal ligand field strength was modulated from weak to strong (L′ = DMF, MeCN, CN). The extent of intracore M–M interactions is gauged by M–M distances, spin ground state persistence, and preference for mixed-valence states as determined by electrochemical comproportionation constants. Coordination of DMF to the [(HL)2Fe6] core leads to weaker Fe–Fe interactions, as manifested by the observation of ground states populated only at lower temperatures (