Kinetically Controlled Reticular Assembly of a Chemically Stable Mesoporous Ni(II)-Pyrazolate Metal–Organic Framework

The application scope of metal–organic
frameworks (MOFs)
is severely restricted by their weak chemical stability and limited
pore size. A robust MOF with large mesopores is highly desired, yet
poses a great synthetic challenge. Herein, two chemically stable Ni­(II)-pyrazolate
MOFs, BUT-32 and -33, were constructed from a conformation-matched
elongated pyrazolate ligand through the isoreticular expansion. The
two MOFs share the same sodalite-type net, but have different pore
sizes due to the network interpenetration in BUT-32. Controlled syntheses
of the two MOFs have been achieved through precisely tuning reaction
conditions, where the microporous BUT-32 was demonstrated to be a
thermodynamically stable product while the mesoporous BUT-33 is kinetically
favored. To date, BUT-32 represents the first example of Ni4-pyrazolate MOF whose structure was unambiguously determined by single-crystal
X-ray diffraction. Interestingly, the kinetic product BUT-33 integrates
2.6 nm large mesopores with accessible Ni­(II) active sites and remarkable
chemical stability even in 4 M NaOH aqueous solution and 1 M Grignard
reagent. This MOF thus demonstrated an excellent catalytic performance
in carbon–carbon coupling reactions, superior to other Ni­(II)-MOFs
including BUT-32. These findings highlight the importance of kinetic
control in the reticular synthesis of mesoporous MOFs, as well as
their superiority in heterogeneous catalysis.