36 research outputs found
Highly Selective Sorption and Separation of CO<sub>2</sub> from a Gas Mixture of CO<sub>2</sub> and CH<sub>4</sub> at Room Temperature by a Zeolitic Organic–Inorganic Ionic Crystal and Investigation of the Interaction with CO<sub>2</sub>
Mixed gas cosorption and gas chromatographic investigations
demonstrate that a zeolitic organic–inorganic ionic crystal
K<sub>2</sub>[Cr<sub>3</sub>O(OOCH)<sub>6</sub>(4-etpy)<sub>3</sub>]<sub>2</sub>[α-SiW<sub>12</sub>O<sub>40</sub>]·2H<sub>2</sub>O [<b>1</b>·2H<sub>2</sub>O] (etpy = ethylpyridine)
with a pore diameter of 3.5 Å possesses high separation ability
of carbon dioxide (kinetic diameter 3.3 Å) over methane (3.76
Å) at room temperature in the presence of water vapor. Monte
Carlo simulation combined with density functional theory calculation
suggests that carbon dioxide molecules diffuse into the one-dimensional
channels and interact initially with the potassium ions and then with
the oxygen atoms of silicododecatungstates, which are confirmed with
carbon dioxide sorption enthalpy and <i>in situ</i> IR spectroscopy
Synthesis and Reversible Transformation of Cu<sub><i>n</i></sub>‑Bridged (<i>n</i> = 1, 2, or 4) Silicodecatungstate Dimers
Three copper-bridged sandwich-type silicodecatungstate
dimers,
TBA<sub>8</sub>[Cu(γ-SiW<sub>10</sub>O<sub>34</sub>)<sub>2</sub>(CH<sub>3</sub>CONH)<sub>2</sub>]·4H<sub>2</sub>O (<b>Cu-1</b>, TBA = tetra-<i>n-</i>butylammonium), TBA<sub>8</sub>H<sub>4</sub>[Cu<sub>2</sub>(γ-SiW<sub>10</sub>O<sub>36</sub>)<sub>2</sub>H<sub>2</sub>O]·11H<sub>2</sub>O·CH<sub>3</sub>COCH<sub>3</sub> (<b>Cu-2</b>), and TBA<sub>8</sub>H<sub>2</sub>[Cu<sub>4</sub>(γ-SiW<sub>10</sub>O<sub>36</sub>)<sub>2</sub>(CH<sub>3</sub>COO)<sub>2</sub>]·5H<sub>2</sub>O (<b>Cu-4</b>)
have been selectively synthesized by reactions of divacant lacunary
TBA<sub>4</sub>[H<sub>4</sub>(γ-SiW<sub>10</sub>O<sub>36</sub>)] (SiW10) with copper acetate in organic media. The copper cation(s)
in <b>Cu-1</b>, <b>Cu-2</b>, and <b>Cu-4</b> possess
square-planar four-coordinate (<b>Cu-1</b>), square-pyramidal
five-coordinate (<b>Cu-2</b>), and octahedral six-coordinate
(<b>Cu-4</b>) geometries, respectively. These compounds can
reversibly be transformed simply by controlling the copper/SiW10 molar
ratios in solutions
Concerted Functions of Anions and Cations in a Molecular Ionic Crystal with Stable Three-Dimensional Micropores
The
molecular ionic crystal [Cr<sub>3</sub>O(OOCCHCH<sub>2</sub>)<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub>]<sub>3</sub>[α-PW<sub>12</sub>O<sub>40</sub>]·15H<sub>2</sub>O [<b>Ia</b>] with
stable three-dimensional micropores and a minimum aperture of 3.3
Å was synthesized with a phosphododecatungstate [α-PW<sub>12</sub>O<sub>40</sub>]<sup>3–</sup> (polyoxometalate, POM)
and a macrocation with acrylate ligands [Cr<sub>3</sub>O(OOCCHCH<sub>2</sub>)<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub>]<sup>+</sup>. The porous structure of <b>Ia</b> was basically constructed
by an arrangement of macrocations forming a six-membered ring: vinyl
groups (CHCH<sub>2</sub>) of adjacent macrocations were aligned
parallel to each other, suggesting a weak dispersion force between
them. A guest-free phase [Cr<sub>3</sub>O(OOCCHCH<sub>2</sub>)<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub>]<sub>3</sub>[α-PW<sub>12</sub>O<sub>40</sub>] [<b>Ib</b>] was
formed by the treatment of <b>Ia</b> in vacuo at room temperature
without any structure change. Compound <b>Ib</b> showed shape-selective
sorption of CO<sub>2</sub> and C<sub>2</sub>H<sub>2</sub> (molecular
size = 3.3 Å) over N<sub>2</sub> (3.6 Å) and methane (3.7
Å), and the sorption enthalpy of C<sub>2</sub>H<sub>2</sub> was
larger than that of CO<sub>2</sub>. The high affinity toward C<sub>2</sub>H<sub>2</sub> was further confirmed as follows: the Monte
Carlo simulations of the optimized geometries of C<sub>2</sub>H<sub>2</sub> in <b>Ib</b> showed that both hydrogen atoms were in
the vicinity of the surface oxygen atoms of POMs. The gas sorption
profiles showed a much faster diffusion for C<sub>2</sub>H<sub>2</sub>. All these results suggest that the anion and cation mainly play
the guest-binding and structure-directing roles, respectively, (i.e.,
concerted functions) in an ionic crystal with stable three-dimensional
micropores
Amphiprotic Properties of a Bis(μ-hydroxo)divanadium(IV)-Substituted γ‑Keggin-Type Silicodecatungstate Containing Two Different Kinds of Hydroxyl Moieties
A bis(μ-hydroxo)divanadium(IV)-substituted
γ-Keggin-type silicodecatungstate, (TBA)<sub>4</sub>[γ-SiV<sup>IV</sup><sub>2</sub>W<sub>10</sub>O<sub>36</sub>(μ-OH)<sub>4</sub>] (<b>1</b>), possesses two different kinds of hydroxyl
groups and can work as an amphiprotic species to accept and donate
proton(s). Dehydrative condensation reactions of <b>1</b> with
methanol and formic acid proceed on more basic hydroxyl groups between
two vanadium atoms without the deprotonation of more acidic hydroxides
between two tungsten atoms to form (TBA)<sub>4</sub>[γ-SiV<sup>IV</sup><sub>2</sub>W<sub>10</sub>O<sub>36</sub>(μ-OH)<sub>3</sub>(μ-OR)] (<b>2·R</b>, R = Me, Et, Pr; <b>3</b>, R = C(O)H), showing Brønsted base properties of the
hydroxyl groups between two vanadium atoms. On the other hand, the
hydroxyl groups between tungsten atoms exhibit Brønsted acid
properties and react with pyridine (Py) and TBAOH to form (TBA)<sub>4</sub>X[γ-SiV<sup>IV</sup><sub>2</sub>W<sub>10</sub>O<sub>37</sub>(μ-OH)<sub>3</sub>] (<b>PyH·4</b>, X = PyH; <b>TBA·4</b>, X = TBA). DFT calculations for [γ-SiV<sup>IV</sup><sub>2</sub>W<sub>10</sub>O<sub>36</sub>(μ-OH)<sub>4</sub>]<sup>4–</sup> in water also support both the acidic
and basic nature of hydroxyl groups in <b>1</b>
Porous Ionic Crystals Modified by Post-Synthesis of K<sub>2</sub>[Cr<sub>3</sub>O(OOCH)<sub>6</sub>(etpy)<sub>3</sub>]<sub>2</sub>[α-SiW<sub>12</sub>O<sub>40</sub>]·8H<sub>2</sub>O through Single-Crystal-to-Single-Crystal Transformation
Post-synthesis
modification of a porous ionic crystal proceeded via two steps (acid
treatment followed by ion-exchange) in an aqueous solution and a single-crystal-to-single-crystal
manner. Compound K<sub>2</sub>[Cr<sub>3</sub>O(OOCH)<sub>6</sub>(etpy)<sub>3</sub>]<sub>2</sub>[α-SiW<sub>12</sub>O<sub>40</sub>]·8H<sub>2</sub>O (etpy = 4-ethylpyridine) [<b>1a</b>] is a porous ionic
crystal with one-dimensional channels, which can accommodate guests
such as water, alcohols, and halocarbons. Crystals of <b>1a</b> were immersed in an aqueous HCl solution (acid treatment), and the
etpy ligand which was exposed to the one-dimensional channel was removed
and exchanged with water. The formula of the resulting compound was
(etpyH<sup>+</sup>)<sub>2</sub>[Cr<sub>3</sub>O(OOCH)<sub>6</sub>(etpy)<sub>2</sub>(H<sub>2</sub>O)]<sub>2</sub>[α-SiW<sub>12</sub>O<sub>40</sub>]·6H<sub>2</sub>O [<b>2a</b>], and K<sup>+</sup> ions, which are potential guest binding sites, were simultaneously
removed by this treatment. Reincorporation of K<sup>+</sup> ions was
attempted by immersion of <b>2a</b> into an aqueous CH<sub>3</sub>COOK solution (ion-exchange), and K<sub>2</sub>[Cr<sub>3</sub>O(OOCH)<sub>6</sub>(etpy)<sub>2.5</sub>(H<sub>2</sub>O)<sub>0.5</sub>]<sub>2</sub>[α-SiW<sub>12</sub>O<sub>40</sub>]·8H<sub>2</sub>O [<b>3a</b>] was formed. Increase in sorption capacity by the two-step
post-synthesis modification was confirmed by sorption isotherms and
Monte Carlo-based simulations using water as a probe molecule. The
role of K<sup>+</sup> ions as water binding sites was confirmed by
water sorption isotherms of alkali metal ion-exchanged compounds
Synthesis and Reversible Transformation of Cu<sub><i>n</i></sub>‑Bridged (<i>n</i> = 1, 2, or 4) Silicodecatungstate Dimers
Three copper-bridged sandwich-type silicodecatungstate
dimers,
TBA<sub>8</sub>[Cu(γ-SiW<sub>10</sub>O<sub>34</sub>)<sub>2</sub>(CH<sub>3</sub>CONH)<sub>2</sub>]·4H<sub>2</sub>O (<b>Cu-1</b>, TBA = tetra-<i>n-</i>butylammonium), TBA<sub>8</sub>H<sub>4</sub>[Cu<sub>2</sub>(γ-SiW<sub>10</sub>O<sub>36</sub>)<sub>2</sub>H<sub>2</sub>O]·11H<sub>2</sub>O·CH<sub>3</sub>COCH<sub>3</sub> (<b>Cu-2</b>), and TBA<sub>8</sub>H<sub>2</sub>[Cu<sub>4</sub>(γ-SiW<sub>10</sub>O<sub>36</sub>)<sub>2</sub>(CH<sub>3</sub>COO)<sub>2</sub>]·5H<sub>2</sub>O (<b>Cu-4</b>)
have been selectively synthesized by reactions of divacant lacunary
TBA<sub>4</sub>[H<sub>4</sub>(γ-SiW<sub>10</sub>O<sub>36</sub>)] (SiW10) with copper acetate in organic media. The copper cation(s)
in <b>Cu-1</b>, <b>Cu-2</b>, and <b>Cu-4</b> possess
square-planar four-coordinate (<b>Cu-1</b>), square-pyramidal
five-coordinate (<b>Cu-2</b>), and octahedral six-coordinate
(<b>Cu-4</b>) geometries, respectively. These compounds can
reversibly be transformed simply by controlling the copper/SiW10 molar
ratios in solutions
Copper-Catalyzed Oxidative Cross-Coupling of <i>H</i>‑Phosphonates and Amides to <i>N</i>‑Acylphosphoramidates
A simple combination of copper(II) acetate (Cu(OAc)<sub>2</sub>) and an appropriate base could promote oxidative cross-coupling of <i>H</i>-phosphonates and amides using air as a terminal oxidant. The substrate scope was broad with respect to both dialkyl <i>H</i>-phosphonates and nitrogen nucleophiles (including oxazolidinone, lactam, pyrrolidinone, urea, indole, and sulfonamide derivatives), giving the corresponding P–N coupling products in moderate to high yields
Redox-Induced Reversible Uptake–Release of Cations in Porous Ionic Crystals Based on Polyoxometalate: Cooperative Migration of Electrons with Alkali Metal Ions
Redox-active porous ionic crystals
based on polyoxometalates (POM)
were synthesized. By treating the crystal with an aqueous solution
of ascorbic acid (reducing reagent) and KCl, one-electron reduction
of POM proceeded followed by simultaneous uptake of K<sup>+</sup>.
Interestingly, the reduction did not proceed without KCl, and the
molecular size of ascorbic acid was too large to enter the porous
crystal lattice. The time courses of reduction and K<sup>+</sup> uptake
were monitored by UV–vis spectroscopy and atomic absorption
spectrometry (AAS), respectively. Both profiles could be reproduced
by the linear driving force (LDF) model with similar rate constants.
The reduced crystal could be oxidized with aqueous chlorine solution
followed by the release of K<sup>+</sup>, and the redox cycles were
reversible. The water sorption properties of the crystals could be
controlled by the types of alkali metal ions incorporated. The Cs<sup>+</sup> uptake and the simultaneous reduction of the crystal proceeded
much faster than in the case of K<sup>+</sup>, which is in line with
the trends in the Gibbs energies of hydration of alkali metal ions.
Complete selectivity to Cs<sup>+</sup> was observed in the uptake
of ions from an aqueous binary mixture of Cs<sup>+</sup> and Na<sup>+</sup>. All these results suggest the cooperative migration of electrons
with alkali metal ions and the redox induced ion-exchange in porous
ionic crystals based on POM
Synthesis and Characterization of Molecular Hexagons and Rhomboids and Subsequent Encapsulation of Keggin-Type Polyoxometalates by Molecular Hexagons
Structural control among hexagonal
(trimer), rhomboidal (dimer), and infinite-chain supramolecular complexes
with three different supporting ligands of ethylenediamine (en), <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine (en*), and 1,2-bis(diphenyl)phosphinoethane
(dppe) [(en)Pd(L)]<sub>3</sub>(OTf)<sub>6</sub> <b>1t·OTf</b>, [(en*)Pd(L)]<sub>2</sub>(PF<sub>6</sub>)<sub>4</sub> <b>2d·PF</b><sub><b>6</b></sub>, and [(dppe)Pd(L)(OTf)<sub>2</sub>]<sub>∞</sub> <b>3·OTf</b> (OTf = trifluoromethane sulfonate;
L = 1,3-bis(4-pyridylethynyl)benzene) in the solid and solution states
was investigated. The encapsulation of a large Keggin-type polyoxometalate
[α-PW<sub>12</sub>O<sub>40</sub>]<sup>3–</sup> by these
complexes was also examined. As the steric bulkiness of the supporting
ligands increased in the order of en < en* < dppe, the hexagonal,
rhomboidal, and infinite-chain structures were obtained, as confirmed
by X-ray crystallography. In solution, equilibrium between the molecular
hexagon (<b>1t·OTf</b>/<b>2t·PF</b><sub><b>6</b></sub>) and the molecular rhomboid (<b>1d·OTf</b>/<b>2d·PF</b><sub><b>6</b></sub>) was observed in
the en/en* ligand systems, whereas <b>3·OTf</b> with the
dppe ligand did not exhibit equilibrium and instead existed as a single
species. These phenomena were established by cold-spray ionization
mass spectroscopy (CSI-MS) and <sup>1</sup>H diffusion ordered NMR
spectroscopy (DOSY). The addition of the highly negatively charged
Keggin-type phosphododecatungstate [α-PW<sub>12</sub>O<sub>40</sub>]<sup>3–</sup> to a solution of <b>2t/2d·PF</b><sub><b>6</b></sub> resulted in the encapsulation of the tungstate
species in the cavity of the molecular hexagon to form {[(en*)Pd(L)]<sub>3</sub>[⊃α-PW<sub>12</sub>O<sub>40</sub>]}(PF<sub>6</sub>)<sub>3</sub> <b>2t·</b>[α-PW<sub>12</sub>O<sub>40</sub>]<sup>3–</sup>, as confirmed by a combination of <sup>1</sup>H and <sup>31</sup>P DOSY and CSI-MS spectral data
Synthesis, Structure Characterization, and Reversible Transformation of a Cobalt Salt of a Dilacunary γ‑Keggin Silicotungstate and Sandwich-Type Di- and Tetracobalt-Containing Silicotungstate Dimers
A cobalt salt of a γ-Keggin
dilacunary silicotungstate, {CoL<sub>5</sub>}<sub>2</sub>[γ-SiW<sub>10</sub>O<sub>34</sub>L<sub>2</sub>] [<b>Co-SiW10</b>; L = <i>N</i>,<i>N</i>-dimethylformamide (DMF) or H<sub>2</sub>O], could be synthesized by the cation-exchange reaction of TBA<sub>4</sub>[γ-H<sub>4</sub>SiW<sub>10</sub>O<sub>36</sub>] (TBA
= tetra-<i>n</i>-butylammonium) with 2 equiv of Co(NO<sub>3</sub>)<sub>2</sub> with respect to TBA<sub>4</sub>[γ-H<sub>4</sub>SiW<sub>10</sub>O<sub>36</sub>] in a mixed solvent of DMF
and acetone (97% yield). Each <b>Co-SiW10</b> was linked by
water molecules via a hydrogen-bonding network. Besides <b>Co-SiW10</b>, various kinds of isostructural <b>M-SiW10</b> could be synthesized
via the same procedure as that for <b>Co-SiW10</b> (M = Mn<sup>2+</sup>, Fe<sup>2+</sup>, Ni<sup>2+</sup>, Cu<sup>2+</sup>, Zn<sup>2+</sup>, and Cd<sup>2+</sup>). By the reaction of <b>Co-SiW10</b> with 1 equiv of TBA<sub>6</sub>[γ-H<sub>2</sub>SiW<sub>10</sub>O<sub>36</sub>] in acetone, a silicotungstate dimer pillared by two
cobalt cations with a significantly slipped dimer configuration, TBA<sub>6</sub>[Co<sub>2</sub>(γ-H<sub>3</sub>SiW<sub>10</sub>O<sub>36</sub>)<sub>2</sub>]·3H<sub>2</sub>O (<b>Co2</b>), could
be synthesized. By the reaction of <b>Co-SiW10</b> with 3 equiv
of TBAOH in acetone, a tetracobalt-containing sandwich-type silicotungstate,
TBA<sub>6</sub>[{Co(H<sub>2</sub>O)}<sub>2</sub>(μ<sub>3</sub>-OH)<sub>2</sub>{Co(H<sub>2</sub>O)<sub>2</sub>}<sub>2</sub>(γ-H<sub>2</sub>SiW<sub>10</sub>O<sub>36</sub>)<sub>2</sub>]·5H<sub>2</sub>O (<b>Co4</b>), could be synthesized. Compound <b>Co4</b> possessed the tetracobalt–oxygen core, [{Co(H<sub>2</sub>O)}<sub>2</sub>(μ<sub>3</sub>-OH)<sub>2</sub>{Co(H<sub>2</sub>O)<sub>2</sub>}<sub>2</sub>]<sup>6+</sup>, identical with those of
previously reported Weakley-type sandwich polyoxometalates, [Co<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>(XM<sub>9</sub>O<sub>34</sub>)<sub>2</sub>]<sup><i>n</i>−</sup> (X = P<sup>5+</sup>, Si<sup>4+</sup>, Ge<sup>4+</sup>, As<sup>5+</sup> or V<sup>5+</sup>; M = Mo<sup>6+</sup> or W<sup>6+</sup>). The reversible transformation
between these three compounds (<b>Co-SiW10</b> ⇆ <b>Co2</b>, <b>Co-SiW10</b> ⇆ <b>Co4</b>, and <b>Co2</b> ⇆ <b>Co4</b>) took place by the addition
and/or subtraction of required components in appropriate solvents,
affording the desired products in high yields (71–93% yields)