Linker Desymmetrization: Access to a Series of Rare-Earth Tetracarboxylate Frameworks with Eight-Connected Hexanuclear Nodes

The exploration of metal–organic
frameworks (MOFs) through
the rational design of building units with specific sizes, geometries,
and symmetries is essential for enriching the structural diversity
of porous solids for applications including storage, separation, and
conversion. However, it is still a challenge to directly synthesize
rare-earth (RE) MOFs with less connected clusters as a thermodynamically
favored product. Herein, we report a systematic investigation on the
influence of size, rigidity, and symmetry of linkers over the formation
of RE-tetracarboxylate MOFs and uncover the critical role of linker
desymmetrization in constructing RE-MOFs with eight-connected hexanuclear
clusters. Our results on nine new RE-MOFs, PCN-50X (X = 1–9), indicate that utilization of
trapezoidal or tetrahedral linkers provides accesses to traditionally
unattainable RE-tetracarboxylate MOFs with 8-c hexanuclear nodes,
while the introduction of square or rectangular linkers during the
assembly of RE-MOFs based on polynuclear clusters typically leads
to the MOFs constructed from 12-c nodes with underlying shp topology. By rational linker design, MOFs with two unprecedented
(4, 8)-c nets, lxl and jun, can also be
obtained. This work highlights linker desymmetrization as a powerful
strategy to enhance MOFs’ structural complexity and access
MOF materials with nondefault topologies that can be potentially used
for separation and catalysis.