Crystallographic Visualization of Postsynthetic Nickel Clusters into Metal–Organic Framework

Postsynthetic
metalation (PSM) has been employed as a robust method
for the postsynthetic modification of metal–organic frameworks
(MOFs). However, the lack of relevant information that can be obtained
for the postsynthetically introduced metallic ions has hindered the
development of PSM applications. Thanks to the advancement in single-crystal
X-ray diffraction (SCXRD) technology, there have been a few recent
examples in which successful postsynthetic introduction of single
metal ions into MOFs occurred at the defined chelating sites. These
works have provided useful explanations about the complicated host–guest
chemistry involved in PSMs. On the other hand, there are only limited
examples with crystallographic snapshots of the postsynthetic installation
of metal clusters into the pores of MOFs using an ordinary SCXRD due
to the loss of crystallinity of parent matrix during the PSM process.
Herein, by the careful selection of starting materials and controlling
the reaction conditions, we report the first crystallographic visualization
of metal clusters inserted into Zr-based MOFs via PSM. The structural
advantages of the parent Zr-MOF, which are inherited from the stable
Zr6 cluster and triazole-containing dicarboxylate ligand,
ensure both the preservation of high crystallinity and the presence
of flexible coordination sites for PSM. Furthermore, PSM of metal
clusters in a MOF pore space enhances stability of the final samples
while also imparting the functionality of a successful catalyst toward
ethylene dimerization reaction. The related construction ideas and
structural information detailed in this work can help lay the foundation
for further advancements using the postmodification of MOFs as well
as open new doors for the utilization of SCXRD technology in the field
of MOFs.