97 research outputs found
Predesign and Systematic Synthesis of 11 Highly Porous Coordination Polymers with Unprecedented Topology
We propose and validate
a simple strategy of vertex connection
that can be used for framework design and pore size/type modulation
to prepare a mother structure and another 10 highly porous isoreticular
frameworks with unprecedented topology. Importantly, the potential
accessible pore volumes (57–71%), pore sizes (6.8–11.
2 Å; 17.0–29.0 Å; 12.5–22.8 Å; 11.9–24.5
Ã…), and the pore shapes of this series of highly porous frameworks
were simultaneously and systematically tuned. Interestingly, the pore
size of IIa [Zn<sub>4</sub>OÂ(L<sup>2</sup>)<sub>2</sub>(BDC)<sub>0.5</sub>]Â{(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>} decreased a little
less than that of IIc [Zn<sub>4</sub>OÂ(L<sup>2</sup>)<sub>2</sub>(2,6-NDC)<sub>0.5</sub>]Â{(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>}; however,
its selectivity of CO<sub>2</sub> toward CH<sub>4</sub> increased
by almost two times
Behavior of Binary Guests in a Porous Coordination Polymer
Controlling the condensed state of multiple guests in
nanoporous
media is critical to many applications, but an understanding of this
phenomenon in pores smaller than a few nanometers is still unavailable.
In this work, we investigate the aggregation state of binary guests,
polyÂ(ethylene glycol) (PEG), and long-chain normal alkanes, in subnanometer
channels of a porous coordination polymer (PCP) by monitoring their
thermal transition behaviors. PEG and alkanes are immiscible in the
bulk and their melting transitions are not affected by each other.
Meanwhile, in the PCP nanochannels, the transition temperature and
the heat of the binary–guest system were significantly different
from when PEG or an alkane was individually included. This suggests
the formation of microscopically segregated domain structures of PEG
and alkane in the host crystal. The transition behaviors gradually
varied by changing the introduction ratio between PEG and alkane,
and thus the aggregation states of the two guests were successfully
controlled by the simple variation of relative amounts. This methodology
offers a promising route to control spatial configurations of multiple
guest molecules in nanoporous matrices for advanced applications
Controlled Synthesis of Anisotropic Polymer Particles Templated by Porous Coordination Polymers
Nonspherical
polymer particles have been efficiently prepared in different morphological
crystals of porous coordination polymers (PCPs) by in situ radical
polymerization of styrene and methylmethacrylate, followed by removal
of the host PCP frameworks in aqueous tetrasodium ethylenediaminetetraacetate
(Na-EDTA) solution. In this replication process, the isolated vinyl
polymer particles retained the size and morphologies of the original
PCP particles, although the polymer chains were not stabilized by
cross-linking. This morphological retention of vinyl polymers after
the isolation from the PCP matrixes was ensured by the rigidity and
porosity of the polymers, which was confirmed by DSC and adsorption
measurements. The unconventional assembly of polymer chains in the
particles is of interest from the viewpoints of functional properties
of the polymer particles
Radical Copolymerization Mediated by Unsaturated Metal Sites in Coordination Nanochannels
Radical copolymerization of methyl
methacrylate (MMA) and styrene
was performed in [TbÂ(1,3,5-benzenetrisbenzoate)]<sub><i>n</i></sub> with coordinatively unsaturated metal sites (UMS) immobilized
along the one-dimensional nanochannels. A drastic increase in the
proportion of MMA units in the resulting copolymers was obtained compared
with that obtained from the corresponding solution polymerization
systems. Simultaneous coordination of MMA to the UMS is the key to
increasing the MMA proportion during the copolymerization in the nanochannels,
which was demonstrated by variable temperature IR measurements and
several controlled experiments
Opening of an Accessible Microporosity in an Otherwise Nonporous Metal–Organic Framework by Polymeric Guests
The development of highly porous
metal–organic frameworks
(MOFs) is greatly sought after, due to their wide range of applications.
As an alternative to the development of new structures, we propose
to obtain new stable configurations for flexible MOFs by insertion
of polymeric guests. The guests prevent the otherwise spontaneous
closing of the host frameworks and result in stable opened forms.
Introduced at a fraction of the maximal capacity, polymer chains cause
an opening of the occupied nanochannels, and because of the MOF reticular
stiffness, this opening is propagated to the neighboring nanochannels
that become accessible for adsorption. Composites were obtained by
in situ polymerization of vinyl monomers in the nanochannels of an
otherwise nonporous MOF, resulting in homogeneously loaded materials
with a significant increase of porosity (<i>S</i><sub>BET</sub> = 920 m<sup>2</sup>/g). In addition, by limiting the accessible
configurations for the framework and forbidding the formation of a
reactive intermediate, the polymeric guest prevented the thermal degradation
of the host MOF even at very low loading (as low as 3 wt %) and increased
its stability domain by more than 200 °C
Integration of Intrinsic Proton Conduction and Guest-Accessible Nanospace into a Coordination Polymer
We
report the synthesis and characterization of a coordination
polymer that exhibits both intrinsic proton conductivity and gas adsorption.
The coordination polymer, consisting of zinc ions, benzimidazole,
and orthophosphate, exhibits a degree of flexibility in that it adopts
different structures before and after dehydration. The dehydrated
form shows higher intrinsic proton conductivity than the original
form, reaching as high as 1.3 × 10<sup>–3</sup> S cm<sup>–1</sup> at 120 °C. We found that the rearranged conduction
path and liquid-like behavior of benzimidazole molecules in the channel
of the framework afforded the high proton conductivity. Of the two
forms of the framework, only the dehydrated form is porous to methanol
and demonstrates guest-accessible space in the structure. The proton
conductivity of the dehydrated form increases by 24 times as a result
of the in situ adsorption of methanol molecules, demonstrating the
dual functionality of the framework. NMR studies revealed a hydrogen-bond
interaction between the framework and methanol, which enables the
modulation of proton conductivity within the framework
Structuralization of Ca<sup>2+</sup>-Based Metal–Organic Frameworks Prepared via Coordination Replication of Calcium Carbonate
The
emergence of metal–organic frameworks (MOFs) as potential candidates
to supplant existing adsorbent types in real-world applications has
led to an explosive growth in the number of compounds available to
researchers, as well as in the diversity of the metal salts and organic
linkers from which they are derived. In this context, the use of carbonate-based
precursors as metal sources is of interest due to their abundance
in mineral deposits and their reaction chemistry with acids, resulting
in just water and carbon dioxide as side products. Here, we have explored
the use of calcium carbonate as a metal source and demonstrate its
versatility as a precursor to several known frameworks, as well as
a new flexible compound based on the 2,5-dihydroxybenzoquinone (H<sub>2</sub>dhbq) linker, CaÂ(dhbq)Â(H<sub>2</sub>O)<sub>2</sub>. Furthermore,
inspired by the ubiquity and unique structures of biomineralized forms
of calcium carbonate, we also present examples of the preparation
of superstructures of Ca-based MOFs via the coordination replication
technique. In all, the results confirm the suitability of carbonate-based
metal sources for the preparation of MOFs and further expand upon
the growing scope of coordination replication as a convenient strategy
for the preparation of structuralized materials
pH-Dependent Interpenetrated, Polymorphic, Cd<sup>2+</sup>- and BTB-based Porous Coordination Polymers with Open Metal Sites
Two polymorphic porous coordination polymers constructed
from Cd<sup>2+</sup> and benzene-1,3,5-tribenzoate and having interpenetrated
two-dimensional (2D) (6,3) net topology and three-dimensional (3D)
(10,3)-b net topology structures were synthesized. The number of single
honeycomb-type layers interpenetrated dictates the dimensionality
of the crystal structures of these two phases. The 2D structure has
two interpenetrated layers, whereas the 3D structure has four interpenetrated
layers. Interestingly, these two polymorphic forms selectively adsorb
CO<sub>2</sub> over N<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, and
C<sub>2</sub>H<sub>6</sub>. Moreover, diffuse reflectance Fourier-transform
infrared spectroscopy of CO<sub>2</sub> adsorbed on these two polymorphic
phases indicates strong interaction between CO<sub>2</sub> and the
open metal sites present on Cd<sup>2+</sup> ions
Preparation of Porous Polysaccharides Templated by Coordination Polymer with Three-Dimensional Nanochannels
Polymerization
of monosaccharide monomers usually suffers from the production of
polysaccharides with ill-defined structures because of the uncontrolled
random reactions among many reactive hydroxyl groups on saccharide
monomers. In particular, rational synthesis of polysaccharides with
porosity approximating molecular dimensions is still in its infancy,
despite their usefulness as drug carriers. Here, we disclose an efficient
synthetic methodology for the preparation of polysaccharides with
controllable mesoporosity in the structure, utilizing [Cu<sub>3</sub>(benzene-1,3,5-tricarboxylate)]<sub><i>n</i></sub> (HKUST-1; <b>1</b>) as templates. Cationic ring-opening polymerization of 1,6-anhydro
glucose was performed in nanochannels of <b>1</b>, followed
by removal of the host frameworks, giving polysaccharide particles
as replicas of the original molds. Nitrogen adsorption measurement
revealed that the obtained polysaccharide particles contained high
mesoporosity in the structure, which could be controlled systematically
depending on the polymerization conditions. Because of the large specific
surface area, tunable porosity and particle size, we could also demonstrate
the capabilities of our polysaccharides for loading and releasing
of a drug molecule and protein
Absorption of CO<sub>2</sub> and CS<sub>2</sub> into the Hofmann-Type Porous Coordination Polymer: Electrostatic versus Dispersion Interactions
Absorption of CO<sub>2</sub> and CS<sub>2</sub> molecules into
the Hofmann-type three-dimensional porous coordination polymer (PCP)
{FeÂ(Pz)Â[PtÂ(CN)<sub>4</sub>]}<sub><i>n</i></sub> (Pz = pyrazine)
was theoretically explored with the ONIOMÂ(MP2.5 or SCS-MP2:DFT) method,
where the M06-2X functional was employed in the DFT calculations.
The binding energies of CS<sub>2</sub> and CO<sub>2</sub> were evaluated
to be −17.3 and −5.2 kcal mol<sup>–1</sup>, respectively,
at the ONIOMÂ(MP2.5:M06-2X) level and −16.9 and −4.4
kcal mol<sup>–1</sup> at the ONIOMÂ(SCS-MP2:M06-2X) level. It
is concluded that CS<sub>2</sub> is strongly absorbed in this PCP
but CO<sub>2</sub> is only weakly absorbed. The absorption positions
of these two molecules are completely different: CO<sub>2</sub> is
located between two Pt atoms, whereas one S atom of CS<sub>2</sub> is located between two Pz ligands and the other S atom is between
two Pt atoms. The optimized position of CS<sub>2</sub> agrees with
the experimentally reported X-ray structure. To elucidate the reasons
for these differences, we performed an energy decomposition analysis
and found that (i) both the large binding energy and the absorption
position of CS<sub>2</sub> arise from a large dispersion interaction
between CS<sub>2</sub> and the PCP, (ii) the absorption position of
CO<sub>2</sub> is mainly determined by the electrostatic interaction
between CO<sub>2</sub> and the Pt moiety, and (iii) the small binding
energy of CO<sub>2</sub> comes from the weak dispersion interaction
between CO<sub>2</sub> and the PCP. Important molecular properties
relating to the dispersion and electrostatic interactions, which are
useful for understanding and predicting gas absorption into PCPs,
are discussed in detail
- …