54 research outputs found
Deconstructing the Crystal Structures of Metal–Organic Frameworks and Related Materials into Their Underlying Nets
Deconstructing the Crystal Structures of Metal–Organic Frameworks and Related Materials into Their Underlying Net
Isomers of Metal–Organic Complex Arrays
Three metal–organic complex arrays (MOCAs) with
a specific sequence of metal centers
as well as that of amino acid units were synthesized. These MOCAs
are also isomers exhibiting a gelation capability dependent on the
location of the metal complexes in the arrays
High Methane Storage Capacity in Aluminum Metal–Organic Frameworks
The use of porous materials to store
natural gas in vehicles requires
large amounts of methane per unit of volume. Here we report the synthesis,
crystal structure and methane adsorption properties of two new aluminum
metal–organic frameworks, MOF-519 and MOF-520. Both materials
exhibit permanent porosity and high methane volumetric storage capacity:
MOF-519 has a volumetric capacity of 200 and 279 cm<sup>3</sup> cm<sup>–3</sup> at 298 K and 35 and 80 bar, respectively, and MOF-520
has a volumetric capacity of 162 and 231 cm<sup>3</sup> cm<sup>–3</sup> under the same conditions. Furthermore, MOF-519 exhibits an exceptional
working capacity, being able to deliver a large amount of methane
at pressures between 5 and 35 bar, 151 cm<sup>3</sup> cm<sup>–3</sup>, and between 5 and 80 bar, 230 cm<sup>3</sup> cm<sup>–3</sup>
Modular Synthesis of Metal–Organic Complex Arrays Containing Precisely Designed Metal Sequences
A modular
synthetic approach is reported for the synthesis of heterometallic
metal–organic complex arrays (MOCAs). Modules of four metal
centers containing three different metals copper(II), nickel(II),
platinum(II), or ruthenium(II) are prepared using a solid-phase polypeptide
synthesis technique and then linked in solution to make MOCAs of eight
metal centers as linear, T-branched, and H-branched compounds. The
MOCA molecular topologies thus have specific unique linear and branched
sequences of metals along the peptide backbone
High Methane Storage Working Capacity in Metal–Organic Frameworks with Acrylate Links
High methane storage capacity in
porous materials is important
for the design and manufacture of vehicles powered by natural gas.
Here, we report the synthesis, crystal structures and methane adsorption
properties of five new zinc metal–organic frameworks (MOFs),
MOF-905, MOF-905-Me<sub>2</sub>, MOF-905-Naph, MOF-905-NO<sub>2</sub>, and MOF-950. All these MOFs consist of the Zn<sub>4</sub>O(−CO<sub>2</sub>)<sub>6</sub> secondary building units (SBUs) and benzene-1,3,5-tri-β-acrylate,
BTAC. The permanent porosity of all five materials was confirmed,
and their methane adsorption measured up to 80 bar to reveal that
MOF-905 is among the best performing methane storage materials with
a volumetric working capacity (desorption at 5 bar) of 203 cm<sup>3</sup> cm<sup>–3</sup> at 80 bar and 298 K, a value rivaling
that of HKUST-1 (200 cm<sup>3</sup> cm<sup>–3</sup>), the benchmark
compound for methane storage in MOFs. This study expands the scope
of MOF materials with ultrahigh working capacity to include linkers
having the common acrylate connectivity
Molecular Retrofitting Adapts a Metal–Organic Framework to Extreme Pressure
Despite numerous
studies on chemical and thermal stability of metal–organic
frameworks (MOFs), mechanical stability remains largely undeveloped.
To date, no strategy exists to control the mechanical deformation
of MOFs under ultrahigh pressure. Here, we show that the mechanically
unstable MOF-520 can be retrofitted by precise placement of a rigid
4,4′-biphenyldicarboxylate (BPDC) linker as a “girder”
to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting
alters how the structure deforms under ultrahigh pressure and thus
leads to a drastic enhancement of its mechanical robustness. While
in the parent MOF-520 the pressure transmitting medium molecules diffuse
into the pore and expand the structure from the inside upon compression,
the girder in the new retrofitted MOF-520-BPDC prevents the framework
from expansion by linking two adjacent secondary building units together.
As a result, the modified MOF is stable under hydrostatic compression
in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical
stability of MOF-520-BPDC prohibits the typical amorphization observed
for MOFs in this pressure range. Direct correlation between the orientation
of these girders within the framework and its linear strain was estimated,
providing new insights for the design of MOFs with optimized mechanical
properties
Molecular Retrofitting Adapts a Metal–Organic Framework to Extreme Pressure
Despite numerous
studies on chemical and thermal stability of metal–organic
frameworks (MOFs), mechanical stability remains largely undeveloped.
To date, no strategy exists to control the mechanical deformation
of MOFs under ultrahigh pressure. Here, we show that the mechanically
unstable MOF-520 can be retrofitted by precise placement of a rigid
4,4′-biphenyldicarboxylate (BPDC) linker as a “girder”
to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting
alters how the structure deforms under ultrahigh pressure and thus
leads to a drastic enhancement of its mechanical robustness. While
in the parent MOF-520 the pressure transmitting medium molecules diffuse
into the pore and expand the structure from the inside upon compression,
the girder in the new retrofitted MOF-520-BPDC prevents the framework
from expansion by linking two adjacent secondary building units together.
As a result, the modified MOF is stable under hydrostatic compression
in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical
stability of MOF-520-BPDC prohibits the typical amorphization observed
for MOFs in this pressure range. Direct correlation between the orientation
of these girders within the framework and its linear strain was estimated,
providing new insights for the design of MOFs with optimized mechanical
properties
Impact of Disordered Guest–Framework Interactions on the Crystallography of Metal–Organic Frameworks
It is a general and
common practice to carry out single-crystal
X-ray diffraction experiments at cryogenic temperatures in order to
obtain high-resolution data. In this report, we show that this practice
is not always applicable to metal–organic frameworks (MOFs),
especially when these structures are highly porous. Specifically,
two new MOFs are reported here, MOF-1004 and MOF-1005, for which the
collection of the diffraction data at lower temperature (100 K) did
not give data of sufficient quality to allow structure solution. However,
collection of data at higher temperature (290 K) gave atomic-resolution
data for MOF-1004 and MOF-1005, allowing for structure solution. We
find that this inverse behavior, contrary to normal practice, is also
true for some well-established MOFs (MOF-177 and UiO-67). Close examination
of the X-ray diffraction data obtained for all four of these MOFs
at various temperatures led us to conclude that disordered guest–framework
interactions play a profound role in introducing disorder at low temperature,
and the diminishing strength of these interactions at high temperatures
reduces the disorder and gives high-resolution diffraction data. We
believe our finding here is more widely applicable to other highly
porous MOFs and crystals containing highly disordered molecules
Chemical Environment Control and Enhanced Catalytic Performance of Platinum Nanoparticles Embedded in Nanocrystalline Metal–Organic Frameworks
Chemical environment
control of the metal nanoparticles (NPs) embedded
in nanocrystalline metal–organic frameworks (nMOFs) is useful
in controlling the activity and selectivity of catalytic reactions.
In this report, organic linkers with two functional groups, sulfonic
acid (−SO<sub>3</sub>H, S) and ammonium (−NH<sub>3</sub><sup>+</sup>, N), are chosen as strong and weak acidic functionalities,
respectively, and then incorporated into a MOF [Zr<sub>6</sub>O<sub>4</sub>(OH)<sub>4</sub>(BDC)<sub>6</sub> (BDC = 1,4-benzenedicarboxylate),
termed UiO-66] separately or together in the presence of 2.5 nm Pt
NPs to build a series of Pt NPs-embedded in UiO-66 (Pt⊂nUiO-66).
We find that these chemical functionalities play a critical role in
product selectivity and activity in the gas-phase conversion of methylcyclopentane
(MCP) to acyclic isomer, olefins, cyclohexane, and benzene. Pt⊂nUiO-66-S
gives the highest selectivity to C<sub>6</sub>-cyclic products (62.4%
and 28.6% for cyclohexane and benzene, respectively) without acyclic
isomers products. Moreover, its catalytic activity was doubled relative
to the nonfunctionalized Pt⊂nUiO-66. In contrast, Pt⊂nUiO-66-N
decreases selectivity for C<sub>6</sub>-cyclic products to <50%
while increases the acyclic isomer selectivity to 38.6%. Interestingly,
the Pt⊂nUiO-66-SN containing both functional groups gave different
product selectivity than their constituents; no cyclohexane was produced,
while benzene was the dominant product with olefins and acyclic isomers
as minor products. All Pt⊂nUiO-66 catalysts with different
functionalities remain intact and maintain their crystal structure,
morphology, and chemical functionalities without catalytic deactivation
after reactions over 8 h
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