Light-Driven Ratchet Mechanism Accelerates Regioselective Metal-Cation Exchange in a Heterobimetallic Helicate

Molecular machines rely on their capacity to exploit non-equilibrium processes to perform work. However, the development of these non-equilibrium processes, such as molecular ratchets, is still in its early stages. Here, we report a diazocine-containing ligand (L) harbouring two distinct chelating coordination sites that can self-sort into dinuclear homo- and heterobimetallic helicates ([Fe^II ₂L](OTf)₄, [Co^II ₂L](OTf)₄, [Zn^II ₂L](OTf)₄, [Zn^IIFe^IIL](OTf)₄, [Zn^IICo^IIL](OTf)₄) with precisely controlled metal cation distribution. The photoisomerisation of the helicates operates via a molecular ratchet mechanism, resulting in metastable diastereomers that shift the system from thermodynamic equilibrium. Continuous white-light irradiation autonomously drives this ratchet process, selectively enriching an out-of-equilibrium pseudo-mesocate structure. Crucially, the ratchet mechanism can significantly accelerate metal-cation exchange from the [Zn^II ₂L](OTf)₄ helicate to the [Zn^IIFe^IIL](OTf)₄ helicate. Thus, the system operates in a manner reminiscent of a "claw machine", selectively seizing Fe^II ions when subjected to a precisely controllable external stimulus. These findings lay the foundation for creating adaptive and reconfigurable supramolecular structures that use non-equilibrium phenomena on a molecular level.