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

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., O ^2- or S ^2- ) 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, [Fe ₂₀ Co ₂₀ ] (1) and [Fe ₁₂ Co ₁₅ ] (2), by creating the "flexibility" through a versatile ligand of bis((1H-imidazol-4-yl)methylene)hydrazine (H ₂ L) and low-coordinate cobalt. Complex 1 features a super-square array of four cyanide-bridged [Fe ₄ Co ₄ ] 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 [Co ₃ L ₃ ] enveloped by a [Fe ₁₂ Co ₁₂ ] 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.
(© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)