Ligand redox non-innocence in the stoichiometric oxidation of Mn ₂(2,5-dioxidoterephthalate) (Mn-MOF-74)

Unsaturated metal sites within the nodes of metal-organic frameworks (MOFs) can be interrogated by redox reagents common to small molecule chemistry. We show, for the first time, that an analogue of the iconic M₂(2,5- dioxidoterephthalate) (M₂DOBDC, MOF-74) class of materials can be stoichiometrically oxidized by one electron per metal center. The reaction of Mn₂DOBDC with C₆H₅ICl₂ produces the oxidized material Cl₂Mn₂DOBDC, which retains crystallinity and porosity. Surprisingly, magnetic measurements, X-ray absorption, and infrared spectroscopic data indicate that the Mn ions maintain a formal oxidation state of +2, suggesting instead the oxidation of the DOBDC ^4- ligand to the quinone DOBDC^2-. These results describe the first example of ligand redox non-innocence in a MOF and a rare instance of stoichiometric electron transfer involving the metal nodes. The methods described herein offer a synthetic toolkit that will be of general use for further explorations of the redox reactivity of MOF nodes.