Formal water oxidation turnover frequencies from MIL-101(Cr) anchored Ru(bda) depend on oxidant concentration

[Ru(bda)(L)2] incorporated into the MIL-101(Cr) metal–organic framework catalyzes water oxidation faster than a homogenous reference, with the number of active catalysts depending on oxidant concentration.

and nitromethane (14 mL) under Ar atmosphere. AlCl3·6H2O (380 mg, 1.6 mmol) and metoxyacetyl chloride (80 mg, 0.74 mmol) were added sequentially to the vigorously stirred suspension. The mixture was heated at 100°C overnight. After cooling to room temperature, the S4 greenish chloromethylated product was collected by centrifugation. The product was activated using water (60 mL) at 60°C for 4 h, ethanol (60 mL) at 85°C for 4 h and after that with THF (60 mL) at 65°C for 4 h. Finally, the greenish powder was collected by centrifugation and dried under vacuum at 80°C.          S13 significant change in the XANES, one expects that these geometric structural changes to affect only the complex HOMO structure. However, one should know that the EXAFS signal's characteristically low signal-to-noise affects data fitting confidence. Therefore, the structural changes observed might not surmount to significant electronic structure changes, which dominate the catalytic process.

Comparison of Cr:Ru ratio between ICP-AES and EDX
XANES analysis: Figure S10 shows the XAS spectra of MIL-101-2@Ru and its molecular reference

Electrochemistry:
Cyclic voltammetry (CV) was performed using a one-compartment, three-electrode configuration connected to an Autolab PGSTAT100 potentiostat controlled with GPES 4.9 software (EcoChemie). The electrode setup included an auxiliary glassy carbon disc (0.071 cm 2 ) working electrode, which was used to monitor the solution between scans, a platinum rod counter electrode, and a Ag/AgCl aqueous reference electrode (sat. KCl(aq), 0.198 V vs. NHE).
The counter electrode and the reference electrode were separated from the working electrode by

Oxygen evolution experiments:
A standard Clark-type oxygraph electrode (Hansatech Instruments), which is separated from the sample solution by a Teflon membrane, was used to check the O2 production.

MIL-101-2@Ru
The MOF sample (1.86 mg) was dissolved in 1 mL H2SO4/H2O2 (1:0.5) and then diluted to 5 mL for ICP-AES analysis. The concentrations of ruthenium and chromium in MIL-101-2@Ru after digestion in con. H2SO4/H2O2 were found to be 1.99 and 67.2 µg/mL respectively.  In each experiment, the MOF suspension was added to the vial, which was sealed and degassed by passing Ar through the solution for 30 min. The total headspace volume was 8.9 mL or 28.7 mL depending on the size of the reaction vial for each experiment. The volume of oxygen was converted to moles using PV = nRT where R = 8.34144 L kPa K −1 mol −1 , T = 298.15 K, P = 101.325 kPa and V = 6.198x10 −3 L.
The amount of Ru catalyst was determined by the catalyst loading (µmol mg −1 ) in [MIL-101-4@Ru as described above, which is 0.101 µmol mg −1 .
The TOF was obtained from the data taken after 5 min by,

Analysis of supernatant solution after catalysis:
The supernatant after catalysis with MIL-101-4@Ru was analyzed by ICP-AES and subject to a second addition of CAN. To MIL-101-4@Ru (2.13 mg, 0.22 μmol Ru) was added 0.67 M CAN under identical condition as shown in Table 1 (0.5 M HNO3, 1 mL). After 5 min, the oxygen evolved was measured by GC. The suspension was centrifuged and filtered, and the supernatant was collected. A second addition CAN (0.67 M) to the supernatant (1 mL) revealed negligible oxygen evolution levels compared to the as-prepared catalytic materials. ICP-AES also showed amounts of leaching of Ru into the solution during catalysis. However, this does not lead to the formation of an active WOC species in solution, considering the low amount of oxygen produced during a second CAN addition to the supernatant. We attribute the presence of Cr in the supernatant to presence of small MIL-101-4@Ru crystallites (less than 200 nm) that are impossible to remove by centrifugation.