Construction of Chimeric Metal–Organic Frameworks with Symmetry-Mismatched Building Blocks

Chimeric metal–organic frameworks (CMOFs) composed
of symmetry-mismatched
inorganic and organic building blocks are rare because the interconnections
between these blocks are topologically demanding. Herein, an MOF with
symmetry-matched building blocks is used as a self-template for the
template-assisted synthesis of CMOFs. Specifically, the post-synthetic
transformation of the [Zn4O(COO)6] clusters
in the self-templating MOF into the [Fe3IIIO(COO)6]+ clusters with symmetry-mismatched trigonal prismatic
site symmetry affords isoreticular CMOFs while maintaining the template
morphology and crystallinity. The framework strain of CMOFs due to
the symmetry-mismatched linkages between their building blocks is
reduced by modulating the conformation of organic building blocks
with torsional degrees of freedom. The further transformation of [Fe3IIIO(COO)6]+-based CMOFs
through redox-facilitated metal exchange using Cr2+ ions
yields highly stable isostructural CMOFs containing [Cr3IIIO(COO)6]+ clusters and exhibiting
stabilities in strongly acidic and moderately basic media comparable
to those of prototypical [Cr3IIIO(COO)6]+-based MOFs with symmetry-matched building blocks. These
results hold significant potential and highlight the vast opportunities
for revisiting well-known yet fragile MOFs built upon the zinc acetate
clusters.