Reversible Redox Activity in Multicomponent Metal–Organic Frameworks Constructed from Trinuclear Copper Pyrazolate Building Blocks

Inorganic functionalization of metal–organic
frameworks
(MOFs), such as incorporation of multiple inorganic building blocks
with distinct metals into one structure and further modulation of
the metal charges, endows the porous materials with significant properties
toward their applications in catalysis. In this work, by an exploration
of the role of 4-pyrazolecarboxylic acid (H2PyC) in the
formation of trinuclear copper pyrazolate as a metalloligand in situ,
four new MOFs with multiple components in order were constructed through
one-pot synthesis. This metalloligand strategy provides multicomponent
MOFs with new topologies (tub for FDM-4 and tap for FDM-5) and is also compatible with a second organic linker for
cooperative construction of complex MOFs (1,4-benzenedicarboxylic
acid for FDM-6 and 2,6-naphthalenedicarboxylic acid for FDM-7). The
component multiplicity of these MOFs originates from PyC’s
ability to separate Cu and Zn on the basis of their differentiated
binding affinities toward pyrazolate and carboxylate. These MOFs feature
reversible and facile redox transformations between CuI3(PyC)3 and CuII3(μ-OH)­(PyC)3(OH)3 without altering the connecting geometries
of the units, thus further contributing to the significant catalytic
activities in the oxidation of CO and aromatic alcohols and the decomposition
of H2O2. This study on programming multiple
inorganic components into one framework and modulating their electronic
structures is an example of functionalizing the inorganic units of
MOFs with a high degree of control.