Postsynthetic Oxidation of the Coordination Site in a Heterometallic Metal–Organic Framework: Tuning Catalytic Behaviors
Yi Han, Michael A. Sinnwell, Robert G. Surbella, Wenjuan Xue, Hongliang Huang, Jian Zheng, Bo Peng, Gaurav Verma, Yang Yang, Lili Liu, Shengqian Ma, Praveen K. Thallapally
Abstract
Postsynthetic modification (PSM) in metal–organic frameworks (MOFs) can introduce multiple functionalities and alter the structural function for the desired application. However, the PSM of the coordination site faces the challenges of structural collapse or incompatibility between the original metal site and the newly formed coordination group. Herein, we developed a novel concept of introducing “primary” and “secondary” nodes, coexisting in a water-stable, Zr-based heterometallic MOF, [Zr6(μ3-OH)8(OH)8][Cu4I(L1)4]2 (1-SH-a, H2L1 = 6-mercaptopyridine-3-carboxylic acid). The postsynthetic oxidation at the coordination site was successfully achieved in the secondary nodes [Cu4I(L1)4]4–, while the robust primary nodes [Zr6(μ3-OH)8(OH)8]8+ stabilized the whole framework to form [Zr6(μ3-OH)8(OH)8][(Cu0.44ICu0.56II(OH)0.56)4(L2)4]2 (1-SO3H, H2L2 = 6-sulfonicotinic acid). Attempts to directly synthesize 1-SO3H through the reactions of Zr(IV), Cu(II), and H2L2 failed. Furthermore, the PSM of 1-SH-a to form 1-SO3H was utilized to tune the catalytic behaviors toward the styrene oxide ring-opening reaction to give an improved regioselectivity of the primary alcohol (A) of ∼99% compared with that of 1-SH-a (∼71%).