Redox Control in a Conducting MOF through Coupled Electronic–Vibronic Effects

Redox control in electrically conducting metal–organic frameworks (MOFs) requires understanding how intercalated cations reshape both electronic structure and lattice thermodynamics. In the nominal A2-Mn-DOBDC anionic framework (A = Li+, Na+, K+), redox potentials and electronic conductivities follow K < Li < Na, contradicting an electrostatic polarization model. Finite-temperature free-energy partitioning shows competing contributions: ΔFEL (electronic term) decreases along Li > Na > K, whereas ΔFVIB (vibrational term) increases along Li < Na < K, producing a maximum stabilization that favors Na and rationalizes the nonintuitive potential ordering. FTIR band shifts track cation-induced systematic mode shifts consistent with cation-dependent vibrational reorganization, and DFT vibrational densities of states with Helmholtz free energies reproduce ΔFVIB trends. Mixed-valence charge transfer with cation-modulated electronic coupling accounts for the conductivity ordering. Na2-Mn-DOBDC delivers a median discharge voltage of ∼3.0 V vs Na+/Na while retaining measurable electronic conductivity, providing a general electronic–vibronic route to tune redox energetics in conducting MOFs.