Single Dispersion of Fe(H 2 O) 2 -Based Polyoxometalate on Polymeric Carbon Nitride for Biomimetic CH 4 Photooxidation.

Direct methane conversion to value-added oxygenates under mild conditions with in-depth mechanism investigation has attracted wide interest. Inspired by methane monooxygenase, the K 9 Na 2 Fe(H 2 O) 2 {[γ-SiW 9 O 34 Fe(H 2 O)]} 2 ·25H 2 O polyoxometalate (Fe-POM) with well-defined Fe(H 2 O) 2 sites is synthesized to clarify the key role of Fe species and their microenvironment toward CH 4 photooxidation. The Fe-POM can efficiently drive the conversion of CH 4 to HCOOH with a yield of 1570.0 µmol g POM -1 and 95.8% selectivity at ambient conditions, much superior to that of [Fe(H 2 O)SiW 11 O 39 ] 5- with Fe(H 2 O) active site, [Fe 2 SiW 10 O 38 (OH)] 2 14- and [P 8 W 48 O 184 Fe 16 (OH) 28 (H 2 O) 4 ] 20- with multinuclear Fe-OH-Fe active sites. Single-dispersion of Fe-POM on polymeric carbon nitride (PCN) is facilely achieved to provide single-cluster functionalized PCN with well-defined Fe(H 2 O) 2 site, the HCOOH yield can be improved to 5981.3 µmol g POM -1 . Systemic investigations demonstrate that the (WO) 4 -Fe(H 2 O) 2 can supply Fe═O active center for C-H activation via forming (WO) 4 -Fe a -O t ···CH 4 intermediate, similar to that for CH 4 oxidation in the monooxygenase. This work highlights a promising and facile strategy for single dispersion of ≈1-2 Å metal center with precise coordination microenvironment by uniformly anchoring nanoscale molecular clusters, which provides a well-defined model for in-depth mechanism research.