Sodium-coupled electron transfer reactivity of metal–organic frameworks containing titanium clusters: the importance of cations in redox chemistry

Stoichiometric reduction reactions of two metal–organic frameworks (MOFs) by the solution reagents [Image: see text] (M = Cr, Co) are described. The two MOFs contain clusters with Ti(8)O(8) rings: Ti(8)O(8)(OH)(4)(bdc)(6); bdc = terephthalate (MIL-125) and Ti(8)O(8)(OH)(4)(bdc-NH(2))(6); bdc-NH(2) = 2-aminoterephthalate (NH(2)-MIL-125). The stoichiometry of the redox reactions was probed using solution NMR methods. The extent of reduction is greatly enhanced by the presence of Na(+), which is incorporated into the bulk of the material. The roughly 1 : 1 stoichiometry of electrons and cations indicates that the storage of e(–) in the MOF is tightly coupled to a cation within the architecture, for charge balance.