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)₂]­[Cu₄(D-cam)₄]·5H₂O·DMF (<b>1</b>; Tt = tris­(triazolyl)­borate, D-H₂cam = d-(+)-camphoric acid or (1<i>R</i>,3<i>S</i>)-1,2,2-trimethyl-1,3-cyclopentane­dicarbox­ylic acid) and [Co­(Tt)₂]­[Cu₄(L-cam)₄]·5H₂O·2DMF (<b>2</b>; L-H₂cam = l-(−)-camphoric acid or (1<i>S</i>,3<i>R</i>)-1,2,2-trimethyl-1,3-cyclo­pentane­dicarbox­ylic acid) were prepared by mixing Cu²⁺, 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, [Zn₄O­(L)₃(DMF)₂]·0.5DMF·H₂O (<b>1</b>; H₂L = 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 [Zn₄O­(R-CO₂)₆(DMF)₂], 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, [Zn₄O­(L)₃(DMF)₂]·0.5DMF·H₂O (<b>1</b>; H₂L = 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 [Zn₄O­(R-CO₂)₆(DMF)₂], 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-Mg₂(dobpdc)

Two new metal–organic frameworks, M₂(dobpdc) (M = Zn (<b>1</b>), Mg (<b>2</b>); dobpdc^4– = 4,4′-dioxido-3,3′-biphenyldicarboxylate), adopting an expanded MOF-74 structure type, were synthesized via solvothermal and microwave methods. Coordinatively unsaturated Mg²⁺ 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 Mg₂(dobpdc)­(mmen)_1.6(H₂O)_0.4 (mmen-Mg₂(dobpdc)). This compound displays an exceptional capacity for CO₂ 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 CO₂ from air, and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40 °C, conditions relevant to CO₂ capture from flue gas. Dynamic gas adsorption/desorption cycling experiments demonstrate that mmen-Mg₂(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 CO₂ in simulated air at 25 °C and 2.52 mmol/g (9.9 wt %) after 15 min of exposure to flowing 15% CO₂ in N₂ at 40 °C. The purity of the CO₂ 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 CO₂ adsorbed. Overall, the performance characteristics of mmen-Mg₂(dobpdc) indicate it to be an exceptional new adsorbent for CO₂ 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-Mg₂(dobpdc)

Two new metal–organic frameworks, M₂(dobpdc) (M = Zn (<b>1</b>), Mg (<b>2</b>); dobpdc^4– = 4,4′-dioxido-3,3′-biphenyldicarboxylate), adopting an expanded MOF-74 structure type, were synthesized via solvothermal and microwave methods. Coordinatively unsaturated Mg²⁺ 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 Mg₂(dobpdc)­(mmen)_1.6(H₂O)_0.4 (mmen-Mg₂(dobpdc)). This compound displays an exceptional capacity for CO₂ 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 CO₂ from air, and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40 °C, conditions relevant to CO₂ capture from flue gas. Dynamic gas adsorption/desorption cycling experiments demonstrate that mmen-Mg₂(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 CO₂ in simulated air at 25 °C and 2.52 mmol/g (9.9 wt %) after 15 min of exposure to flowing 15% CO₂ in N₂ at 40 °C. The purity of the CO₂ 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 CO₂ adsorbed. Overall, the performance characteristics of mmen-Mg₂(dobpdc) indicate it to be an exceptional new adsorbent for CO₂ 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>)­(N₃)]·H₂O (<b>1</b>·H₂O; H₂<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>)­(N₃)] (<b>2</b>; H₂<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_ax···N_ax–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(H₂L)­(bdc)]­·1.4DEF­·0.6H₂O (<b>1</b>; H₂L = 1,4-di­(1H-imidazol-4-yl)­benzene, H₂bdc = terephthalic acid), [Zn­(H₂L)­(bdc)]­·1.5DMF­·1.2H₂O (<b>2</b>), and [Zn­(H₂L)­(L)_0.5(bdc)_0.5]­·formamide­·H₂O (<b>3</b>) were prepared under the solvothermal conditions in DEF/H₂O, DMF/H₂O, and formamide/H₂O 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 N₂, H₂, and CO₂, characteristic of permanent porosity in the flexible framework, while the gases of N₂ and H₂ 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 I₂ 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(H₂L)­(bdc)]­·1.4DEF­·0.6H₂O (<b>1</b>; H₂L = 1,4-di­(1H-imidazol-4-yl)­benzene, H₂bdc = terephthalic acid), [Zn­(H₂L)­(bdc)]­·1.5DMF­·1.2H₂O (<b>2</b>), and [Zn­(H₂L)­(L)_0.5(bdc)_0.5]­·formamide­·H₂O (<b>3</b>) were prepared under the solvothermal conditions in DEF/H₂O, DMF/H₂O, and formamide/H₂O 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 N₂, H₂, and CO₂, characteristic of permanent porosity in the flexible framework, while the gases of N₂ and H₂ 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 I₂ 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^VMn^III Bimetallic Chains Composed of a Blocked W Hexacyanide Precursor: Geometry-Related Magnetic Couplings and Magnetostructural Correlation

Five one-dimensional bimetallic W^VMn^III complexes <b>1</b>–<b>5</b>, consisting of [W­(CN)₆(bpy)]⁻ anions and [Mn­(Schiff base)]⁺ 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_ax (ax = axial) bond length increases when moving from <b>1</b> to <b>2</b>, with the Mn–N_ax–C_ax 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_ax bond lengths are similar across all the samples, the increase in the Mn–N_ax–C_ax angles accounts for the enhanced magnetic strength. Notably, a correlation between structure and magnetic exchange coupling is established for the first time in W^VMn^III bimetallic systems based on the [W­(CN)₆(bpy)]⁻ precursor