Ion-Electron Coupling-Driven Redox Behavior in Metal–Organic Frameworks

Journal of the American Chemical Society · 2026-04-21

Redox-active metal–organic frameworks (MOFs) have long been proposed as electronic transport platforms, yet the microscopic origin of their conductivity remains debated. A theoretical demonstration reveals charge transport in a Zn(pyrazole–naphthalene diimide (NDI)) MOF arising not from delocalized band-like states but from redox hopping between discrete linker sites. Using ab initio molecular dynamics simulations combined with electronic structure analysis, we established a direct link among electron injection, structural reorganization, and transport. Electron accumulation proceeds sequentially and site-selectively from imide and carbonyl groups of the NDI core progressively involving pyrazole N atoms at higher reduction states, through a hierarchy of redox-active sites. In contrast, Zn nodes remain essentially redox-inactive, which confirms their structural role. Density-of-states analysis corroborates a transport regime dominated by linker-centered states with evolving p-character upon reduction, resulting in dynamically reconfigured conduction networks. Real-time trajectories reveal anisotropic linker-to-linker electron transfer modulated by counterion coordination. This cooperative ion–electron regime emerges from potential energy surface collapse into a single low-barrier transition (ΔG‡ ≈ 45 meV), where ionic and electronic motions evolve adiabatically on the same free-energy landscape. Elucidating redox conductivity in Zn(pyrazole–NDI) MOFs provides a theoretical framework for use in neuromorphic computing and related technologies.

Origin of Stabilization of Ligand-Centered Mixed Valence Ruthenium Azopyridine Complexes: DFT Insights for Neuromorphic Applications

The Journal of Physical Chemistry Letters · 2025-06-10

Redox-driven conductance changes are critical processes in molecular- and coordination-complex-based memristive thin films and devices that are envisioned for neuromorphic technologies, but fundamental mechanisms of conductance switching are not fully understood. Here, we explore charge disproportionation (CD) processes in [RuIIL2](PF6)2 molecular systems that intrinsically involve interfragment charge transfer (IFCT). Using a combination of ab initio molecular dynamics simulation (AIMD), time-dependent density functional theory (TD-DFT), and density functional theory (DFT) calculations, we investigate the electron transfer mechanisms and the roles of temperature and cell volumetric expansion in facilitating the counterion movements and electronic transitions required for low-cost IFCT and charge redistribution. A detailed analysis of the density of states and TD-DFT calculations highlights that unpaired electrons play a crucial role in low-energy transitions, with the azo (N═N) groups of the ligand serving as the primary sites for electronic transport between molecular fragments, further stabilizing the asymmetric state. Localization of added electrons on azo ligands occurs with negligible change at the Ru centers, supported by atomic volume expansions up to +4.74 bohr3, and goes along with a progressive reduction of the HOMO–LUMO gap across redox states, suggesting enhanced conductivity. The TD-DFT analysis reveals a dominant IFCT excitation at 2082.76 nm in the doubly reduced (22) state, while a stabilization energy of 1.20 eV of the asymmetric (13) state relative to the symmetric (22) state is predicted by constrained DFT. Periodic DFT and AIMD simulations emulating a molecular film show that the stabilization of the asymmetric state, relative to a symmetric one, translates in net charge separation values (order of ∼0.33 e) that are strongly linked to increased counterion mobility (average counterion displacements exceeding 0.7 Å per atom during CD events) and the involvement of azo groups in electron redistribution. These findings, which align with previously reported experimental and computational data, provide key insights into the IFCT mechanisms and electronic transport facilitated by azo groups, with important implications for redox-driven memristive and neuromorphic technologies.

Structural and Electronic Complexities of a Sulfur‐Bridged Di‐Iron Complex Composed of Mono‐ and Di‐Nitrosyl Units

Advanced Science · 2025-10-27

Abstract The delocalized, thermodynamically stable cation, [(N 2 S 2 )Fe(NO)•Fe(NO) 2 ] + , an adduct of mono‐nitrosyl and dinitrosyl iron units, is analyzed to address the unusual stability of the sulfur‐bridged diiron complex in its three overall redox levels, +, 0, and −. X‐ray diffraction and myriad spectroscopic techniques probe products of sequential electron uptake in the corresponding neutral and anionic species. Conundrums include unified blueshifts of the overall 3‐band, ν(NO), pattern with added electrons. One‐electron reduction changes the anti‐ferromagnetically coupled, S = 0, cationic diiron species to the neutral analog, S = ½, with unpaired spin mainly localized on the MNIU, which decreases its ∠Fe–N–O angle by 10 degrees in response to the extra electron density. Subsequent reduction to the anionic species, S = 1, involves a major geometric change at the MNIU, which moves the Fe in {Fe(NO)} 8 out of the N 2 S 2 plane. Site‐specific 15 N labeling of nitrosyl in the MNIU confirms the IR analysis and shows rapid NO exchange between the MNIU/DNIU (mono‐nitrosyl iron unit/dinitrosyl iron unit) pairs during its synthesis at RT. Mössbauer spectroscopy, S K‐edge XAS, and molecular orbital calculations confirm the ability of NO and the versatility of sulfur bridges to buffer and distribute electrons, a key to their major importance in metalloenzymes.

Unveiling a Distinct Switching Mechanism Based on Transition Metal Co-Ordination Complexes

ECS Meeting Abstracts · 2025-11-24

Resistive switching behavior in Cobalt- and Iron based molecular complexes with 2-phenyl azopyridine ligand has been explored in metal-insulator-metal (MIM) structures. While the devices exhibit switching between high-resistance and low-resistance states under an applied electric field, our findings indicate that this behavior is not solely governed by the intrinsic properties of the complexes in itself. Instead, extrinsic factors such as device architecture play a significant role in the observed switching behavior in these types of complexes. Time-of flight secondary ion mass spectroscopy (TOF-SIMS) spectroscopic analyses combined surface profilometry measurements and electrical characterizations suggest that the mechanism involves redox-driven charge trapping/detrapping or filamentary conduction, but the lack of consistency and reproducibility limits its practical applicability. These results highlight the challenges in using transition metal-based complexes for resistive memory applications including hardware based neuromorphic computing and suggest that their suitability for such applications could be limited.

Vibrational Couplings in the NO Stretch Region in Diiron Trinitrosyl Complexes

ChemRxiv · 2025-09-11

Two-dimensional infrared spectroscopy offers unique capabilities for probing vibrational coupling in complex metal--ligand systems. In this paper, we combine two-dimensional infrared spectroscopy with vibrational perturbation theory to investigate vibrational coupling in a diiron trinitrosyl complex across three stable redox states. Although these systems are challenging for electronic structure methods, we demonstrate that key features of experimental 2D IR spectra can be accurately reproduced using reduced-dimensional anharmonic calculations with physically motivated parameter adjustments, including harmonic frequency scaling and dephasing time optimization. Analysis reveals that N--O stretching modes maintain high locality across all redox states, with coupling patterns that directly reflect variations in Fe--N bond strength. Using curvilinear coordinate analysis, we demonstrate these differences result from systematic changes in cubic anharmonic force constants rather than mode delocalization. Our results establish N--O stretches as sensitive probes of metal--ligand bonding strength, expanding the toolkit for studying biologically relevant nitrosyl complexes.

Sustainable Synthesis of Polycarbonates and Polythiocarbonates from Biomass-Based Eugenol-Furoic Acid-Derived Monomer and CO₂ and COS: Computational Insights

Macromolecules · 2025-05-16 · 7 citations

In recent years, chemists worldwide have made tremendous progress in synthesizing sustainable polymers using monomers derived from renewable feedstocks. This transition is driven by the continuous adverse accumulation of nonbiodegradable, petroleum-based polymers in the ecosystem, as well as achieving long-term goals such as economic sustainability and the depletion of nonrenewable resources. Herein, we report the sustainable synthesis of an epoxide monomer derived exclusively from the renewables eugenol and furoic acid and its copolymerization with CO2 and its sulfur congener carbonyl sulfide in the presence of the binary catalysts (salophen)CoX or (salen)CrX and onium salts to selectively afford regioselective polycarbonates or polymonothiocarbonates in very good yields. The use of propylene carbonate was shown to be an effective and safer alternative solvent to methylene chloride for performing these polymerization reactions. Importantly, unlike what is observed using the sterically nonencumbered propylene oxide monomer, the (salen)CoX and (salophen)CoX binary catalyst systems displayed strikingly different reactivities with the eugenol-based epoxide. That is, only (salophen)CoX was found to selectively provide polycarbonates in excellent yields under mild reaction conditions. This observation has been shown to be strongly supported by DFT computational studies, which illustrate the importance of designing catalysts with tailored ligand frameworks. TGA and DSC measurements reveal these copolymers to be stable up to 240 °C, with relatively high glass-transition (Tg) temperatures of 95 °C. The eugenol-derived polycarbonate fully degraded under basic conditions within one h at ambient temperature quantitatively to the diol, which is readily converted to the corresponding epoxide, making the copolymerization/depolymerization partially circular. On the other hand, the closely related polymonothiocarbonate is quite stable to degradation under identical reaction conditions.

A sulfur-templated Ni–Ni′ coordination polymer that relies on a polarizable nickel nitrosyl hub

Dalton Transactions · 2024-12-17 · 1 citations

The templating properties of a diazanickel- cis -dithiolate towards triphenylphosphinegold (d 10 -Au + ) inspired the synthesis of {Ni-(NO)} 10 as a redox-active and structurally mobile S-based adduct which was then condensed with into a coordination polymer.

CCDC 2258956: Experimental Crystal Structure Determination

The Cambridge Structural Database · 2024-01-06

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 2302283: Experimental Crystal Structure Determination

The Cambridge Structural Database · 2024-01-07

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 2302282: Experimental Crystal Structure Determination

The Cambridge Structural Database · 2024-01-07

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.