15 research outputs found
Two Homochiral Bimetallic Metal–Organic Frameworks Composed of a Paramagnetic Metalloligand and Chiral Camphorates: Multifunctional Properties of Sorption, Magnetism, and Enantioselective Separation
Two
porous metal–organic frameworks [Co(Tt)<sub>2</sub>][Cu<sub>4</sub>(D-cam)<sub>4</sub>]·5H<sub>2</sub>O·DMF (<b>1</b>; Tt = tris(triazolyl)borate, D-H<sub>2</sub>cam = d-(+)-camphoric acid or (1<i>R</i>,3<i>S</i>)-1,2,2-trimethyl-1,3-cyclopentanedicarboxylic acid)
and [Co(Tt)<sub>2</sub>][Cu<sub>4</sub>(L-cam)<sub>4</sub>]·5H<sub>2</sub>O·2DMF (<b>2</b>; L-H<sub>2</sub>cam = l-(−)-camphoric acid or (1<i>S</i>,3<i>R</i>)-1,2,2-trimethyl-1,3-cyclopentanedicarboxylic
acid) were prepared by mixing Cu<sup>2+</sup>, Co(Tt), and camphoric
acid under solvothermal conditions. The structures of <b>1</b> and <b>2</b> reveal that the two-dimensional layers composed
of chiral ligands and Cu-Cu paddlewheel units are connected through
the metalloligands to form three-dimensional networks. It is noted
that these solids show multifunctional properties such as gas
adsorption onto the pores of the frameworks, antiferromagnetic coupling
between spin carriers, and a small enantioselective separation of
racemic alcohols
Reversible Structural Flexibility and Sensing Properties of a Zn(II) Metal–Organic Framework: Phase Transformation between Interpenetrating 3D Net and 2D Sheet
A three-dimensional Zn(II) framework,
[Zn<sub>4</sub>O(L)<sub>3</sub>(DMF)<sub>2</sub>]·0.5DMF·H<sub>2</sub>O (<b>1</b>; H<sub>2</sub>L = 3,3′-dimethoxybiphenyl-4,4′-dicarboxylic
acid) was prepared under a solvothermal reaction in DMF. The structure
reveals that the 3-fold interpenetration is stabilized in the framework
with a distinct secondary building unit of the formula [Zn<sub>4</sub>O(R-CO<sub>2</sub>)<sub>6</sub>(DMF)<sub>2</sub>], slightly different
from that of MOF-5. Phase transformations in <b>1</b> occur
reversibly via two pathways of solvent exchange/resolvation and activation/resolvation,
which is indicative of the presence of extensive structural flexibility.
Nitrobenzene among tested solvents is selectively detected by <b>1</b>, and the sensing event was operating repeatedly. The three-dimensional
framework of <b>1</b> with 3-fold interpenetration is uniquely
converted to the two-dimensional Cu phase with no interpenetration,
reflecting a drastic dimensionality variation
Reversible Structural Flexibility and Sensing Properties of a Zn(II) Metal–Organic Framework: Phase Transformation between Interpenetrating 3D Net and 2D Sheet
A three-dimensional Zn(II) framework,
[Zn<sub>4</sub>O(L)<sub>3</sub>(DMF)<sub>2</sub>]·0.5DMF·H<sub>2</sub>O (<b>1</b>; H<sub>2</sub>L = 3,3′-dimethoxybiphenyl-4,4′-dicarboxylic
acid) was prepared under a solvothermal reaction in DMF. The structure
reveals that the 3-fold interpenetration is stabilized in the framework
with a distinct secondary building unit of the formula [Zn<sub>4</sub>O(R-CO<sub>2</sub>)<sub>6</sub>(DMF)<sub>2</sub>], slightly different
from that of MOF-5. Phase transformations in <b>1</b> occur
reversibly via two pathways of solvent exchange/resolvation and activation/resolvation,
which is indicative of the presence of extensive structural flexibility.
Nitrobenzene among tested solvents is selectively detected by <b>1</b>, and the sensing event was operating repeatedly. The three-dimensional
framework of <b>1</b> with 3-fold interpenetration is uniquely
converted to the two-dimensional Cu phase with no interpenetration,
reflecting a drastic dimensionality variation
Capture of Carbon Dioxide from Air and Flue Gas in the Alkylamine-Appended Metal–Organic Framework mmen-Mg<sub>2</sub>(dobpdc)
Two new metal–organic frameworks, M<sub>2</sub>(dobpdc)
(M = Zn (<b>1</b>), Mg (<b>2</b>); dobpdc<sup>4–</sup> = 4,4′-dioxido-3,3′-biphenyldicarboxylate), adopting
an expanded MOF-74 structure type, were synthesized via solvothermal
and microwave methods. Coordinatively unsaturated Mg<sup>2+</sup> cations
lining the 18.4-Å-diameter channels of <b>2</b> were functionalized
with <i>N</i>,<i>N</i>′-dimethylethylenediamine
(mmen) to afford Mg<sub>2</sub>(dobpdc)(mmen)<sub>1.6</sub>(H<sub>2</sub>O)<sub>0.4</sub> (mmen-Mg<sub>2</sub>(dobpdc)). This compound
displays an exceptional capacity for CO<sub>2</sub> adsorption at
low pressures, taking up 2.0 mmol/g (8.1 wt %) at 0.39 mbar and 25
°C, conditions relevant to removal of CO<sub>2</sub> from air,
and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40 °C, conditions
relevant to CO<sub>2</sub> capture from flue gas. Dynamic gas adsorption/desorption
cycling experiments demonstrate that mmen-Mg<sub>2</sub>(dobpdc) can
be regenerated upon repeated exposures to simulated air and flue gas
mixtures, with cycling capacities of 1.05 mmol/g (4.4 wt %) after
1 h of exposure to flowing 390 ppm CO<sub>2</sub> in simulated air
at 25 °C and 2.52 mmol/g (9.9 wt %) after 15 min of exposure
to flowing 15% CO<sub>2</sub> in N<sub>2</sub> at 40 °C. The
purity of the CO<sub>2</sub> removed from dry air and flue gas in
these processes was estimated to be 96% and 98%, respectively. As
a flue gas adsorbent, the regeneration energy was estimated through
differential scanning calorimetry experiments to be 2.34 MJ/kg CO<sub>2</sub> adsorbed. Overall, the performance characteristics of mmen-Mg<sub>2</sub>(dobpdc) indicate it to be an exceptional new adsorbent for
CO<sub>2</sub> capture, comparing favorably with both amine-grafted
silicas and aqueous amine solutions
Phase Transformation, Exceptional Quenching Efficiency, and Discriminative Recognition of Nitroaromatic Analytes in Hydrophobic, Nonporous Zn(II) Coordination Frameworks
Five-fold interpenetrated
Zn(II) frameworks (<b>1</b> and <b>2</b>) have been prepared,
and an irreversible phase transformation from <b>1</b> to <b>2</b> is found to occur through a dissolution–recrystallization
process. Compound <b>1</b> exhibits the highest quenching efficiency
(>96%) for nitrobenzene at 7 ppm among luminescent coordination
polymers. Selective discrimination of nitroaromatic molecules including <i>o</i>-nitrophenol (<i>o</i>-NP), <i>p</i>-nitrophenol (<i>p</i>-NP), 2,4-dinitrophenol (DNP), and
2,4,6-trinitrophenol (TNP) is realized in <b>1</b> and <b>2</b> as a result of the fact that the framework–analyte
interaction affords characteristic emission signals. This observation
is the first case of a nonporous coordination framework for such discriminative
detection. Notably, significant hydrophobicity is evident in the framework <b>1</b> because of its surface roughness, which accounts for the
enhanced quenching ability
Capture of Carbon Dioxide from Air and Flue Gas in the Alkylamine-Appended Metal–Organic Framework mmen-Mg<sub>2</sub>(dobpdc)
Two new metal–organic frameworks, M<sub>2</sub>(dobpdc)
(M = Zn (<b>1</b>), Mg (<b>2</b>); dobpdc<sup>4–</sup> = 4,4′-dioxido-3,3′-biphenyldicarboxylate), adopting
an expanded MOF-74 structure type, were synthesized via solvothermal
and microwave methods. Coordinatively unsaturated Mg<sup>2+</sup> cations
lining the 18.4-Å-diameter channels of <b>2</b> were functionalized
with <i>N</i>,<i>N</i>′-dimethylethylenediamine
(mmen) to afford Mg<sub>2</sub>(dobpdc)(mmen)<sub>1.6</sub>(H<sub>2</sub>O)<sub>0.4</sub> (mmen-Mg<sub>2</sub>(dobpdc)). This compound
displays an exceptional capacity for CO<sub>2</sub> adsorption at
low pressures, taking up 2.0 mmol/g (8.1 wt %) at 0.39 mbar and 25
°C, conditions relevant to removal of CO<sub>2</sub> from air,
and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40 °C, conditions
relevant to CO<sub>2</sub> capture from flue gas. Dynamic gas adsorption/desorption
cycling experiments demonstrate that mmen-Mg<sub>2</sub>(dobpdc) can
be regenerated upon repeated exposures to simulated air and flue gas
mixtures, with cycling capacities of 1.05 mmol/g (4.4 wt %) after
1 h of exposure to flowing 390 ppm CO<sub>2</sub> in simulated air
at 25 °C and 2.52 mmol/g (9.9 wt %) after 15 min of exposure
to flowing 15% CO<sub>2</sub> in N<sub>2</sub> at 40 °C. The
purity of the CO<sub>2</sub> removed from dry air and flue gas in
these processes was estimated to be 96% and 98%, respectively. As
a flue gas adsorbent, the regeneration energy was estimated through
differential scanning calorimetry experiments to be 2.34 MJ/kg CO<sub>2</sub> adsorbed. Overall, the performance characteristics of mmen-Mg<sub>2</sub>(dobpdc) indicate it to be an exceptional new adsorbent for
CO<sub>2</sub> capture, comparing favorably with both amine-grafted
silicas and aqueous amine solutions
Synthesis, Structures, and Magnetic Properties of End-to-End Azide-Bridged Manganese(III) Chains: Elucidation of Direct Magnetostructural Correlation
The
two one-dimensional chain compounds [Mn(<b>L1</b>)(N<sub>3</sub>)]·H<sub>2</sub>O (<b>1</b>·H<sub>2</sub>O; H<sub>2</sub><b>L1</b> = 2,2′-((1<i>E</i>,1′<i>E</i>)-ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)diphenol)
and [Mn(<b>L2</b>)(N<sub>3</sub>)] (<b>2</b>; H<sub>2</sub><b>L2</b> = 2,2′-((1<i>E</i>,1′<i>E</i>)-2,2-dimethylpropane-1,3-diyl)bis(azan-1-yl-1-ylidene)-bis(phenylmethan-1-yl-1-ylidene)diphenol)
bridged by single end-to-end azides were prepared via a self-assembly
process. Each Mn(III) ion exhibits a characteristic Jahn–Teller
elongation along the chain direction. For both compounds, antiferromagnetic
interactions between Mn(III) spins within a chain are transmitted
through the azide ligands, together with the apparent occurrence of
spin canting at low temperatures. Remarkably, the coupling constants
(<i>J</i>) for <b>1</b> and <b>2</b> exceed
those reported for end-to-end azide-linked Mn(III) systems. A systematic
magnetostructural relationship based on the torsion angle is established
in terms of the torsion angle Mn–N<sub>ax</sub>···N<sub>ax</sub>–Mn (ax = axial) for the first time
Interpenetration Control, Sorption Behavior, and Framework Flexibility in Zn(II) Metal–Organic Frameworks
Three
Zn(II) frameworks [Zn(H<sub>2</sub>L)(bdc)]·1.4DEF·0.6H<sub>2</sub>O (<b>1</b>; H<sub>2</sub>L = 1,4-di(1H-imidazol-4-yl)benzene,
H<sub>2</sub>bdc = terephthalic acid), [Zn(H<sub>2</sub>L)(bdc)]·1.5DMF·1.2H<sub>2</sub>O (<b>2</b>), and [Zn(H<sub>2</sub>L)(L)<sub>0.5</sub>(bdc)<sub>0.5</sub>]·formamide·H<sub>2</sub>O (<b>3</b>) were prepared under the solvothermal conditions
in DEF/H<sub>2</sub>O, DMF/H<sub>2</sub>O, and formamide/H<sub>2</sub>O solvent pairs, respectively. All compounds are commonly based on
the adamantanoid three-dimensional networks that are mutually entangled
to form a 3-fold (<b>1</b>) to 4-fold (<b>2</b>) to 5-fold
interpenetrating <b>dia</b> structure (<b>3</b>). The
solvent pairs used in the reactions are primarily responsible for
the variation of such interpenetration degree. It is noted that the
reaction time, temperature, and reactant ratio applied in the present
system (<b>2</b>) did not lead to the interpenetration change.
The activated sample (<b>1a</b>) shows the gas uptake of N<sub>2</sub>, H<sub>2</sub>, and CO<sub>2</sub>, characteristic of permanent
porosity in the flexible framework, while the gases of N<sub>2</sub> and H<sub>2</sub> are not adsorbed on <b>2</b> and <b>3</b>. The porous compound (<b>1</b>) also exhibits the reversible
inclusion and release of I<sub>2</sub> in MeOH. Interestingly, <b>2</b> reveals the reversible structural transformation during
the activation–resolvation process where the solid can be activated
through two routes (solvent exchange/desolvation and direct desolvation).
However, there is no appreciable structural flexibility upon solvent
exchange in <b>3</b> with 5-fold interpenetration, indicating
that this framework is more robust, compared to <b>1</b> and <b>2</b> with lower interpenetration degrees
Interpenetration Control, Sorption Behavior, and Framework Flexibility in Zn(II) Metal–Organic Frameworks
Three
Zn(II) frameworks [Zn(H<sub>2</sub>L)(bdc)]·1.4DEF·0.6H<sub>2</sub>O (<b>1</b>; H<sub>2</sub>L = 1,4-di(1H-imidazol-4-yl)benzene,
H<sub>2</sub>bdc = terephthalic acid), [Zn(H<sub>2</sub>L)(bdc)]·1.5DMF·1.2H<sub>2</sub>O (<b>2</b>), and [Zn(H<sub>2</sub>L)(L)<sub>0.5</sub>(bdc)<sub>0.5</sub>]·formamide·H<sub>2</sub>O (<b>3</b>) were prepared under the solvothermal conditions
in DEF/H<sub>2</sub>O, DMF/H<sub>2</sub>O, and formamide/H<sub>2</sub>O solvent pairs, respectively. All compounds are commonly based on
the adamantanoid three-dimensional networks that are mutually entangled
to form a 3-fold (<b>1</b>) to 4-fold (<b>2</b>) to 5-fold
interpenetrating <b>dia</b> structure (<b>3</b>). The
solvent pairs used in the reactions are primarily responsible for
the variation of such interpenetration degree. It is noted that the
reaction time, temperature, and reactant ratio applied in the present
system (<b>2</b>) did not lead to the interpenetration change.
The activated sample (<b>1a</b>) shows the gas uptake of N<sub>2</sub>, H<sub>2</sub>, and CO<sub>2</sub>, characteristic of permanent
porosity in the flexible framework, while the gases of N<sub>2</sub> and H<sub>2</sub> are not adsorbed on <b>2</b> and <b>3</b>. The porous compound (<b>1</b>) also exhibits the reversible
inclusion and release of I<sub>2</sub> in MeOH. Interestingly, <b>2</b> reveals the reversible structural transformation during
the activation–resolvation process where the solid can be activated
through two routes (solvent exchange/desolvation and direct desolvation).
However, there is no appreciable structural flexibility upon solvent
exchange in <b>3</b> with 5-fold interpenetration, indicating
that this framework is more robust, compared to <b>1</b> and <b>2</b> with lower interpenetration degrees
Cyanide-Bridged W<sup>V</sup>Mn<sup>III</sup> Bimetallic Chains Composed of a Blocked W Hexacyanide Precursor: Geometry-Related Magnetic Couplings and Magnetostructural Correlation
Five one-dimensional bimetallic W<sup>V</sup>Mn<sup>III</sup> complexes <b>1</b>–<b>5</b>, consisting of [W(CN)<sub>6</sub>(bpy)]<sup>−</sup> anions
and [Mn(Schiff base)]<sup>+</sup> cations,
were prepared. The central coordination geometry around each W atom
is determined as a distorted dodecahedron (DD) for <b>1</b> and <b>2</b>, and a distorted square antiprism (SAPR) for <b>3</b>–<b>5</b>. Magnetic analyses demonstrate that compounds <b>1</b>, <b>4</b>, and <b>5</b> exhibit antiferromagnetic
interactions between magnetic centers, which are different from the
ferromagnetic couplings in <b>2</b> and <b>3</b>. For
the distorted DD geometry, the Mn–N<sub>ax</sub> (ax = axial)
bond length increases when moving from <b>1</b> to <b>2</b>, with the Mn–N<sub>ax</sub>–C<sub>ax</sub> angle remaining
constant. The elongation of the bond length is responsible for the
reduction in orbital overlap and consequent ferromagnetic coupling
in <b>2</b>. In comparison, for <b>3</b>–<b>5</b> with the distorted SAPR geometry, given that the Mn–N<sub>ax</sub> bond lengths are similar across all the samples, the increase
in the Mn–N<sub>ax</sub>–C<sub>ax</sub> angles accounts
for the enhanced magnetic strength. Notably, a correlation between
structure and magnetic exchange coupling is established for the first
time in W<sup>V</sup>Mn<sup>III</sup> bimetallic systems based on
the [W(CN)<sub>6</sub>(bpy)]<sup>−</sup> precursor