The modular structure of metal−organic frameworks (MOFs) makes them promising platforms for catalyst design and for elucidating structure/performance relationships in catalysis. In this work, we systematically varied the composition of the metal nodes (Fe 2 M) of the MOF PCN-250 and used density functional theory (DFT) to identify promising catalysts for light alkane C−H bond activation. Oxidative dehydrogenation (ODH) of alkanes was studied using N 2 O as the oxidant to understand the reactivity of the oxocentered Fe 2 M nodes found in PCN-250, where the Fe ions are in the +3 oxidation state and M is a metal with the oxidation state of +2. We show that the N 2 O activation barrier is positively correlated with the oxygen-binding energy at the metal center, and the C−H activation barrier is negatively correlated with this same quantity. For clusters containing early transition metals, oxygen binds strongly, facilitating N 2 O activation but hindering C−H activation. To validate the DFT predictions, we synthesized and tested PCN-250(Fe 2 M) with M = Mn, Fe, Co, and Ni and found that PCN-250(Fe 2 Mn) and PCN-250(Fe 3 ) are more active than PCN-250(Fe 2 Co) and PCN-250(Fe 2 Ni) in agreement with the DFT predictions, demonstrating the power of DFT calculations to predict and identify promising MOF catalysts for alkane C−H bond activation in advance of experiments.

Density functional theory is used to study the tunability of trigonal prismatic SBUs found in metal–organic frameworks (MOFs) such as MIL-100, MIL-101, and PCN-250/MIL-127 of chemical composition M3+ 2M2+(μ3-O)­(RCOO)6 for the partial oxidation of methane to methanol. We performed a combinatorial screening by varying the composition of the trimetallic node (M1 3+)2(M2 2+) (where M1 and M2 = V, Cr, Mn, Fe, Co, and Ni) and calculated the reaction pathway on both M1 and M2 sites. The systematic replacement of metals in the trimetallic cluster allowed us to study the influence of spectator atoms on the catalytic activity of a specific metal site in the cluster toward the N2O activation and C–H bond activation steps of the reaction. In the screening, we identified the top-performing node compositions with predicted barriers lower than those already reported for experimentally tested MOFs with trigonal prismatic SBUs. This work demonstrates the opportunity to tune the catalytic activity of MOFs for redox reactions by changing their metal node composition.

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Using density functional theory (DFT), we studied the catalytic activity of iron oxide nanoclusters that mimic the structure of the active site in the soluble form of methane monooxygenase (sMMO) for the partial oxidation of methane to methanol. Using N 2 O as the oxidant, we consider a radical-rebound mechanism and a concerted mechanism for the oxidation of methane on either a bridging oxygen (O b ) or a terminal oxygen (O t ) active site. We find that the radical-rebound pathway is preferred over the concerted pathway by 40−50 kJ/mol, but the desorption of methanol and the regeneration of the oxygen site are found to be the highest barriers for the direct conversion of methane to methanol with these catalysts. As demonstrated by a population analysis, the O x (x = b or t) site behaves as an oxygen radical during the H abstraction, and the [Fe + −O x − ] site behaves as a Lewis acid−base pair during the concerted C−H cleavage. Molecular orbital decomposition analysis further demonstrates electron transfer during the oxidation and reduction steps of the reaction. High-level multireference calculations were also carried out to further assess the DFT results. Understanding how these systems behave during the proposed reaction pathways provides new insights into how they can be tuned for methane partial oxidation.

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