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., 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.