Remarkable
Structural Diversity between Zr/Hf and
Rare-Earth MOFs via Ligand Functionalization and the Discovery of
Unique (4, 8)‑c and (4, 12)-connected Frameworks
posted on 2020-09-04, 16:24authored byGiasemi
K. Angeli, Danai Batzavali, Katerina Mavronasou, Constantinos Tsangarakis, Tobias Stuerzer, Holger Ott, Pantelis N. Trikalitis
Ligand
modification in MOFs provides great opportunities not only
for the development of functional materials with new or enhanced properties
but also for the discovery of novel structures. We report here that
a sulfone-functionalized tetrahedral carboxylate-based ligand is capable
of directing the formation of new and fascinating MOFs when combined
with Zr4+/Hf4+ and rare-earth metal cations
(RE) with improved gas-sorption properties. In particular, the resulting
M-flu-SO2 (M: Zr, Hf) materials display a
new type of the augmented flu-a net, which is different
as compared to the flu-a framework formed by the nonfunctionalized
tetrahedral ligand. In terms of properties, a remarkable increase
in the CO2 uptake is observed that reaches 76.6% and 61.6%
at 273 and 298 K and 1 bar, respectively. When combined with REs,
the sulfone-modified linker affords novel MOFs, RE-hpt-MOF-1 (RE: Y3+, Ho3+, Er3+), which
displays a fascinating (4, 12)-coordinated hpt net, based
on nonanuclear [RE9(μ3-Ο)2(μ3-ΟΗ)12(−COO)12] clusters that serve as hexagonal prismatic building blocks.
In the absence of the sulfone groups, we discovered that the tetrahedral
linker directs the formation of new RE-MOFs, RE-ken-MOF-1
(RE: Y3+, Ho3+, Er3+, Yb3+), that display an unprecedented (4, 8)-coordinated ken net based on nonanuclear RE9-clusters, to serve as bicapped
trigonal prismatic building units. Successful activation of the representative
member Y-ken-MOF-1 reveals a high BET surface area and
total pore volume reaching 2621 m2 g–1 and 0.95 cm3 g–1, respectively. These
values are the highest among all RE MOFs based on nonanuclear clusters
and some of the highest in the entire RE family of MOFs. The present
work uncovers a unique structural diversity existing between Zr/Hf
and RE-based MOFs that demonstrates the crucial role of linker design.
In addition, the discovery of the new RE-hpt-MOF-1 and
RE-ken-MOF-1 families of MOFs highlights the great opportunities
existing in RE-MOFs in terms of structural diversity that could lead
to novel materials with new properties.