pH-Dependent Proton Conducting Behavior in a Metal-Organic Framework Material

A porous metal-organic framework (MOF), [Ni-2-(dobdc)(H2O)2]center dot 6H(2)O (Ni-2(dobdc) or Ni-MOF-74; dobdc(4) = 2,5-dioxido-1,4-benzenedicarboxylate) with hexagonal channels was synthesized using a microwave-assisted solvothermal reaction. Soaking Ni-2(dobdc) in sulfuric acid solutions at different pH values afforded new proton-conducting frameworks, H@Ni-2(dobdc). At pH 1.8, the acidified MOF shows proton conductivity of 2.2 x 10(-2) S cm(-1) at 80 degrees C and 95% relative humidity (RH), approaching the highest values reported for MOFs. Proton conduction occurs via the Grotthuss mechanism with a significantly low activation energy as compared to other proton-conducting MOFs. Protonated water clusters within the pores of H@Ni-2(dobdc) play an important role in the conduction process

Selective CO2 adsorption and proton conductivity in the two-dimensional Zn(II) framework with protruded water molecules and flexible ether linkers

A two-dimensional (2D) Zn(II) metal-organic framework with flexible aryl ether linkers and water molecules exposed to the pores was prepared. The supramolecular three-dimensional (3D) network is generated by the presence of extensive pi-pi contacts, which could be responsible for gas uptake. The water molecules and oxygen atoms from the flexible linkers create a polar environment within the integrated framework, leading to simultaneous selective CO2 adsorption and proton conductivity in the two-dimensional Zn(II) framework

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

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

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

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

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

Sulfate-Incorporated Co(II) Coordination Frameworks with Bis-imidazole Bridging Ligands Constructed by Covalent and Noncovalent Interactions

Three 3D supramolecular networks, [Co­(H₂L1)₂]·(SO₄)·2H₂O (<b>1</b>), [Co­(H₂L1)­(SO₄)­(H₂O)­(DMF)] (<b>2</b>), and [Co­(H₂L2)­(SO₄)­(H₂O)] (<b>3</b>), were prepared by reacting Co­(II) sulfate with the rigid bis-imidazoles of 1,4-di­(1<i>H</i>-imidazol-4-yl)­benzene (H₂L1) and 1,3-di­(1<i>H</i>-imidazol-4-yl)­benzene (H₂L2) in solvothermal conditions. Compounds <b>1</b> and <b>2</b> containing the H₂L1 ligand were isolated under different solvent-pair ratios. The structure of <b>1</b> can be described as a 6-fold interpenetrating 3D <b>dia</b> net in which the sulfate anions are positioned in the void spaces to balance the overall charge of the framework. In comparison, complex <b>2</b> shows a rectangular 2D grid consisting of 1D sulfate-bridged chains linked by H₂L1. When H₂L2 is used in the reaction, the complex <b>3</b> having a 3D interdigitaed network with helical chains is formed, which is the first example of an H₂L2-connected coordination polymer. The sulfate ions essentially contribute to the entanglement of the structures through extensive hydrogen bonding. Magnetic measurements for <b>2</b> indicate that very weak ferromagnetic interactions are operative between anisotropic Co­(II) centers via sulfate bridges