Benzoic acid modulators that "cap" the Zr 6 -oxo-hydroxo cluster nodes in UiO-66 metal-organic frameworks can be removed to increase the number of "open" sites (i.e., those that are terminated with [μ 1 -OH + μ 1 -OH 2 ]) up to 5 per node, enabling the "decapped" materials to exhibit enhanced catalytic activity in the oxidation of methyl phenyl sulfide. Computational modeling reveals that the labile Zr-μ 1 -OH groups on these open sites are likely converted into Zr-μ 1 -OOH species that are active in oxidizing the sulfide as well as its sulfoxide product. In solvents such as CH 3 CN and CH 2 Cl 2 , the sulfoxide product can additionally replace the aquo ligands of the Zr-μ 1 -OH 2 moieties to increase the concentration of the sulfoxide adjacent to the active Zr-μ 1 -OOH species, resulting in overoxidation to the sulfone. However, the use of CH 3 OH, a solvent that can compete with the sulfoxide and suppress this binding mode, can retard the overoxidation and lead to higher selectivities for the sulfoxide product.
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