Manipulating Electron‐Transfer Events in [Fe₄Co₄] Cubes via a Mixed‐Ligand Approach: The Impact of Elastic Frustration

Abstract

The engineering of intermolecular interaction is challenging but critical for magnetically switchable molecules. Here, we prepared two cyanide‐bridged [Fe4Co4] cube complexes via the alkynyl‐ and alcohol‐functionalized trispyrazoyl capping ligands. The alkynyl‐functionalized complex 1 exhibited a thermally‐induced incomplete metal‐to‐metal electron transfer (MMET) behaviour at around 220 K, while the mixed alkynyl/alcohol‐functionalized cube of 2 showed a complete and abrupt MMET behaviour at 232 K. Remarkably, both compounds showed a long‐lived photo‐induced metastable state up to 200 K. The crystallographic study demonstrated that the incomplete transition of 1 was likely due to the possible elastic frustration originating from the competition between the anion‐propagated elastic interactions and inter‐cluster alkynyl‐alkynyl & CH‐alkynyl interactions, whereas the latter are eliminated in 2 as a result of the partial substitution by the alcohol‐functionalized ligand. Additionally, the introduction of chemically distinguishable cobalt centers within the cube unit of 2 did not lead to a two‐step but a one‐step transition, possibly because of the strong ferroelastic intramolecular interaction through the cyanide bridges.