Hierarchically Assembled Gigantic Fe/Co Cyanometallate Clusters Exhibiting Electron Transfer Behavior Above Room Temperature

Abstract The construction of large and complex supramolecular architectures through self‐assembly is at the forefront of contemporary coordination chemistry. Notwithstanding great success in various systems using anionic bridges (e.g., O²⁻ or S²⁻) or organic ligands (e.g., pyridine or carboxylate ligands), the assembly of large cyanide‐bridged clusters with increasing nuclearity remains a formidable synthetic challenge. In this study, it is achieved in preparing two heterometallic cyanometallate clusters with unprecedented complexity, [Fe₂₀Co₂₀] (1) and [Fe₁₂Co₁₅] (2), by creating the “flexibility” through a versatile ligand of bis((1H‐imidazol‐4‐yl)methylene)hydrazine (H₂L) and low‐coordinate cobalt. Complex 1 features a super‐square array of four cyanide‐bridged [Fe₄Co₄] cube subunits as the corners that are interconnected by four additional [FeCo] units, resulting in a torus‐shaped architecture. Complex 2 contains a lantern‐like core‐shell cluster with a triple‐helix kernel of [Co₃L₃] enveloped by a [Fe₁₂Co₁₂] shell. The combined structure analysis and mass spectrometry study reveal a hierarchical assembly mechanism, which sheds new light on constructing cyanometallate nanoclusters with atomic precision. Moreover, complex 1 undergoes a thermally induced electron‐transfer‐coupled spin transition (ETCST) between the diamagnetic {Fe^II_LS(µ‐CN)Co^III_LS} and paramagnetic {Fe^III_LS(µ‐CN)Co^II_HS} configurations (LS = low spin, HS = high spin) above room temperature, representing the largest molecule displaying electron transfer and spin transition characteristic.