Host–Guest-Induced Remote Charge Amplification in Ruthenium Complexes Enables Entropy Engineering of Redox Reactions

Controlling redox thermodynamics without perturbing the primary metal coordination of redox-active complexes remains a major challenge in molecular design. Here we propose a chemical strategy based on the secondary coordination sphere (SCS) engineering, in which host–guest encapsulation and release of metal ion at spatially remote crown-ether sites enables tuning of the net charge in those complexes. A crown-ether-functionalized tris(bipyridyl) ruthenium complex (Ru-crown15) selectively binds two Li+ ions in a stepwise manner, effectively increasing the net charge of the complex through host–guest interaction. Temperature-dependent electrochemical measurements reveal that the redox entropy increases with the number of binding Li+ ions, which is in good agreement with a Born-type solvation model. This long-range modulation of thermodynamic parameters highlights the SCS engineering as a versatile approach for molecular-level entropy control in redox systems and offers a route to tune the thermogalvanic responses.