Fig. 4. Effect of[ adding cryptand to reduced MIL-125 (3 equiv. + 1 equiv of Na⁺), and reduction of MIL-125 with and [Na·cryptand]TFSI. (A) Schematic of this reaction. (B) ¹H NMR spectra (d₈-THF + CD₃CN, 4 : 1 v/v) MIL-125 + 3 equiv. + 3 equiv. NaTFSI + 0 (red), 0.2 (yellow), 0.4 (green), 0.6 (light blue), 0.8 (dark blue), and 1.0 (purple) equiv. cryptand (per Ti₈ node). The two peaks indicated by the arrow correspond to free (right) and Na-bound (left) cryptand. (C) Plot of e^– in MIL-125 versus equivs of cryptand added (left axis), and equiv. of Na⁺ in solution (right axis). Orange circles: equivs Na⁺ associated with the reduced MIL-125, derived from the chemical shift. Blue circles: equivs associated with the reduced MIL-125, derived from the change in integration of the resonance. Black circles: total extent of reduction (sum of blue and orange). Light green diamonds: equiv. Na⁺ in solution, derived from the amount of Na⁺ still associated with reduced MIL-125. Dark green diamonds: equiv. of Na⁺ in solution, from integration of the cryptand/cryptand-sodium resonances. Open circles: number of e^– in MIL-125 (per Ti₈ node) for the converse reaction: addition of 3 equiv. of and 1 equiv. of [Na·cryptand]TFSI.