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Self-assembled metallacyles and cages formed via coordination chemistry have been used as catalysts to enforce 4H + /4e − reduction of oxygen to water with an emphasis on attenuating the formation of hydrogen peroxide. That said, the kinetically favored 2H + /2e − reduction to H 2 O 2 is critically important to industry. In this work we report the synthesis, characterization, and electrochemical benchmarking of a hexa-porphyrin cube which catalyses the electrochemical reduction of molecular oxygen to hydrogen peroxide. An established sub-component self-assembly approach was used to synthesize the cubic free-base porphryin topologies from 2-pyridinecarboxaldehyde, tetra-4-aminophenylporphryin (TAPP), and Fe(OTf) 2 (OTf − = trifluoromethansulfonate). Then, a tandem metalation/transmetallation was used to introduce Co( ii ) into the porphyrin faces of the cube, and exchange with the Fe( ii ) cations at the vertices, furnishing a tetrakaideca cobalt cage. Electron paramagnetic resonance studies on a Cu( ii )/Fe( ii ) analogue probed radical interactions which inform on electronic structure. The efficacy and selectivity of the CoCo-cube as a catalyst for hydrogen peroxide generation was investigated using hydrodynamic voltammetry, revealing a higher selectivity than that of a mononuclear Co( ii ) porphyrin (83% versus ∼50%) with orders of magnitude enhancement in standard rate constant ( k s = 2.2 × 10 2 M −1 s −1 versus k s = 3 × 10 0 M −1 s −1 ). This work expands the use of coordination-driven self-assembly beyond ORR to water by exploiting post-synthetic modification and structural control that is associated with this synthetic method.
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This content will become publicly available on August 9, 2026
Selective self-assembly of discrete 2D and 3D porphyrinoid architectures using a directional-bonding approach
Herein, we report the coordination-driven self-assembly of a diazaporphyrin plate and a porphyrin prism, made using the same Ru-benzo molecular clip and 2:1 diruthenium acceptor to tetrapyridyl donor stoichiometry, and discuss characterization techniques used to distinguish the two. We describe how 1H NMR data can distinguish between plate and prism geometries based on peak shifts and splitting in the context of molecular symmetries. DOSY spectra show changes in hydrodynamic radius from the monomeric porphyrin to the prism (4.78 Å to 15.2 Å) and diazaporphyrin to plate (6.02 Å to 12.2 Å) consistent with the increase in size upon assembly. High resolution mass spectrometry provides further evidence for plate and prism, where specific peaks at diagnostic m/z values unequivocally establish the stoichiometry of assembly. Electronic absorption spectroscopy revealed a marked increase in molar absorptivity upon self-assembly. These results establish how molecular characterization techniques may be used to distinguish between possible self-assembly outcomes when a given building block may be encoded with directionality that is suitable for more than one geometry.
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- Award ID(s):
- 1847950
- PAR ID:
- 10636114
- Publisher / Repository:
- Taylor and Francis
- Date Published:
- Journal Name:
- Journal of Coordination Chemistry
- ISSN:
- 0095-8972
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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