Crystalline to Crystalline Phase Transformations in Six Two-Dimensional Dynamic Metal–Organic Frameworks: Syntheses, Characterizations, and Sorption Studies

Six dynamic metal–organic frameworks, namely, {[Cd­(1,4-bib)­(glut)]·(4H₂O)}_<i>n</i> (<b>1</b>), {[Zn­(1,4-bib)­(glut)]·(4H₂O)}_<i>n</i> (<b>2</b>), {[Co­(1,4-bib)­(3,5-pydc)]·(2H₂O)}_<i>n</i> (<b>3</b>), {[Mn­(1,4-bib)­(3,5-pydc)]·(2H₂O)}_<i>n</i> (<b>4</b>), {[Zn­(1,4-bib)­(3-mglut)]·(4H₂O)}_<i>n</i> (<b>5</b>), and {[Zn­(1,4-bib)­(2,2′-dmglut)]·(2H₂O)}_<i>n</i> (<b>6</b>) from 1-(4-(1<i>H</i>-imidazole-1-yl)­butyl)-1<i>H</i>-imidazole (1,4-bib) using four different dicarboxylic acids salt [disodium glutarate (Na₂glut), pyridine-3,5-dicarboxylate (3,5-pydc), 3-methyl glutarate (3-mglut), 2,2′-dimethyl glutarate (Na₂2,2′-dmglut)], and four different divalent transition metal ions have been synthesized. Out of these, the structure of compound <b>3</b> has been previously reported although synthesized in different method, whereas the rest of the compounds are new. All of these synthesized compounds are characterized by single crystal and powder X-ray diffraction and other physicochemical methods. All the compounds exhibit 2D structure as evident by single crystal X-ray studies. Interestingly, all of these compounds show crystalline to crystalline phase transformation. Variable temperature PXRD study indicates compounds <b>1</b> and <b>6</b> show single-step phase transformation and the rest show two-step phase transformation upon desolvation. All of these transformations have also been established by IR spectroscopy. Among the structural transformations listed, <b>1</b>–<b>5</b> show reversible crystalline to crystalline phase transformation on desolvation and resolvation, whereas <b>6</b> shows an irreversible transformation. All of these transformations are thoroughly investigated by PXRD and IR spectroscopy. Sorption studies with CO₂ and N₂ were also performed for all the metal–organic frameworks and characteristic surface adsorptions are found in all the cases

Azo Functionalized 5‑Nitro-1,3-benzenedicarboxylate Based Coordination Polymers with Different Dimensionality and Functionality

Five azo-functionalized coordination polymers (CPs), namely, [Zn­(azbpy)­(NO₂-bdc)­·H₂O]_<i>n</i> (<b>1</b>), [Zn­(azbpy)­(NO₂-bdc)]_<i>n</i>­·3H₂O (<b>2</b>), {[Cd­(azbpy)­(NO₂-bdc)­·H₂O]­·2H₂O}_<i>n</i> (<b>3</b>), {[Mn­(azbpy)₂­(NO₂-bdc)]₂}_<i>n</i> (<b>4</b>), and {[Co­(azbpy)­(NO₂-bdc)­(H₂O)₂]­[Co­(azbpy)_0.5­(NO₂-bdc)­(H₂O)₃]}_<i>n</i> (<b>5</b>) have been synthesized using different transition metal salts with 5-nitro-1,3-benzenedicarboxylate (NO₂-bdc^2–) and 4,4′-azobispyridine (azbpy) ligand using a slow diffusion technique at room temperature. The complexes <b>1</b>–<b>5</b> were characterized by single crystal X-ray diffraction analysis, elemental analysis, infrared spectroscopy (IR), powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). In the solid state, compound <b>1</b> shows a wavy one-dimensional (1D) ladder; constructed through the N,N′-donor azbpy and NO₂-bdc^2– ligands with the metal centers, whereas compound <b>2</b> exhibits a bilayer two-dimensional (2D) sheet containing a wavy 1D ladder of metal-carboxylate, and compound <b>3</b> shows a stairlike wavy 2D sheet. Compound <b>4</b> exhibits a novel 2-fold interdigitated 2D sheet of two similar layers containing pendent azbpy ligands, whereas compound <b>5</b> displays a polythreaded 2D structure with an intercalated 1D chain into the pore. The solid state luminescence properties of <b>1</b>–<b>3</b> along with free N,N′-donor azbpy ligand have been performed at room temperature, where all the complexes <b>1</b>–<b>3</b> show azbpy ligand based luminescence property. The gas and solvent vapor adsorption study have been performed for compounds <b>2</b>–<b>4</b>, and the dehydrated frameworks of compounds <b>2</b>–<b>4</b> exhibit selective CO₂ adsorption at 195 K over N₂ (at both 77 and 195 K) due to the strong interactions between polar pore walls of dehydrated frameworks with the CO₂ molecule having quadruple moment

Four 3D Cd(II)-Based Metal Organic Hybrids with Different N,N′-Donor Spacers: Syntheses, Characterizations, and Selective Gas Adsorption Properties

Four new metal organic frameworks with bivalent cadmium, disodium succinate (Na₂suc), and four different N,N′-donor ligands, i.e., {[Cd­(L1)­(suc)]­·(H₂O)₃}_<i>n</i> (<b>1</b>), {[Cd­(L2)­(suc)]­·(H₂O)₂}_<i>n</i> (<b>2</b>), {[Cd­(L3)­(suc)]­·(H₂O)₄}_<i>n</i> (<b>3</b>), {[Cd₃(L4)₃(suc)₂(H₂O)₂]­·(NO₃)₂ (H₂O)₄}_<i>n</i> (<b>4</b>) [L1 = 2,5-bis-(4-pyridyl)-3,4-diaza-2,4-hexadiene, L2 = <i>trans</i> 4,4′-azobispyridine, L3 = 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene, L4 = 1, 2-bis­(4-pyridyl) ethane and suc = succinate dianion] have been synthesized at room temperature and characterized by single-crystal X-ray diffraction and other physicochemical methods. Structure determination reveals that compounds <b>1</b> and <b>2</b> show honeycomb-like three-dimensional (3D) architecture with water-filled channels. The dehydrated frameworks of <b>1</b> and <b>2</b> exhibit hydrogen and carbon dioxide adsorption properties. In compound <b>3</b>, change of linker (linear to bent) led to the blockage of such regular channels which also affected the porosity and adsorption properties of its dehydrated framework. In <b>4</b>, the used spacer is linear but the resulting 3D framework contains blocked channels filled with nitrate (NO₃^–) anions and lattice water

Four 3D Cd(II)-Based Metal Organic Hybrids with Different N,N′-Donor Spacers: Syntheses, Characterizations, and Selective Gas Adsorption Properties

Four new metal organic frameworks with bivalent cadmium, disodium succinate (Na₂suc), and four different N,N′-donor ligands, i.e., {[Cd­(L1)­(suc)]­·(H₂O)₃}_<i>n</i> (<b>1</b>), {[Cd­(L2)­(suc)]­·(H₂O)₂}_<i>n</i> (<b>2</b>), {[Cd­(L3)­(suc)]­·(H₂O)₄}_<i>n</i> (<b>3</b>), {[Cd₃(L4)₃(suc)₂(H₂O)₂]­·(NO₃)₂ (H₂O)₄}_<i>n</i> (<b>4</b>) [L1 = 2,5-bis-(4-pyridyl)-3,4-diaza-2,4-hexadiene, L2 = <i>trans</i> 4,4′-azobispyridine, L3 = 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene, L4 = 1, 2-bis­(4-pyridyl) ethane and suc = succinate dianion] have been synthesized at room temperature and characterized by single-crystal X-ray diffraction and other physicochemical methods. Structure determination reveals that compounds <b>1</b> and <b>2</b> show honeycomb-like three-dimensional (3D) architecture with water-filled channels. The dehydrated frameworks of <b>1</b> and <b>2</b> exhibit hydrogen and carbon dioxide adsorption properties. In compound <b>3</b>, change of linker (linear to bent) led to the blockage of such regular channels which also affected the porosity and adsorption properties of its dehydrated framework. In <b>4</b>, the used spacer is linear but the resulting 3D framework contains blocked channels filled with nitrate (NO₃^–) anions and lattice water

Selective CO₂ Adsorption by Nitro Functionalized Metal Organic Frameworks

Two nitro functionalized Cu­(II)-MOFs exhibit high CO₂ uptake with nice selectivity over other gases like H₂, N₂, and CH₄, which is potentially important for the removal of carbon dioxide from industrial flue gas and natural gas. Here the selective CO₂ adsorption by these MOFs is primarily due to the presence of suitable voids with −NO₂ group functionalized pore walls in the dehydrated framework, which is unprecedented

Two Series of Isostructural Coordination Polymers with Isomeric Benzenedicarboxylates and Different Azine Based N,N′-Donor Ligands: Syntheses, Characterization and Magnetic Properties

Seven coordination polymers (CPs) with two types of framework structures, namely, {[M­(4-bpdb)­(1,3-bdc)]­·(4-bpdb)_0.5}_<i>n</i> [M = Mn (<b>1</b>), Fe (<b>2</b>), and Co (<b>3</b>)], and {[M­(4-bpdh)­(1,4-bdc)]}_<i>n</i> (M = Mn (<b>4</b>), Fe (<b>5</b>), Co (<b>6</b>), and Cd (<b>7</b>)] have been synthesized through the slow diffusion technique using 1,3-bdc and 1,4-bdc ligands with two different azine based N,N′-donor linkers [1,3-bdc = benzene-1,3-dicarboxylate, 1,4-bdc = benzene-1,4-dicarboxylate, 4-bpdb = <i>N,N</i>′-bis-pyridin-4-ylmethylene-hydrazine and 4-bpdh = <i>N,N</i>′-bis-(1-pyridin-4-yl-ethylidene)-hydrazine]. Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and powder X-ray diffraction (PXRD) analysis. Compounds <b>1</b>–<b>3</b> are isostructural and feature a two-dimensional (2D) framework structure formed by pillaring the one-dimensional [M­(1,3-bdc)]_<i>n</i> double chains through 4-bpdb linkers. In all cases of compounds <b>1</b>–<b>3</b>, free 4-bpdb linkers are present in the lattice and lattice 4-bpdb ligands are involved in π–π and C–H···π interactions with bridging 1,3-bdc and 4-bpdb ligands, to afford three-dimensional (3D) supramolecular structures. Compounds <b>4</b>–<b>7</b> are also isostructural and here the bridging of 1,4-bdc with the divalent metal centers forms a 2D layer of [M­(1,4-bdc)]_<i>n</i> which is further pillared by 4-bpdh to form a 3D pillared-layer framework. Variable temperature magnetic measurements of two sets of isostructural complexes (<b>1</b>–<b>3</b> and <b>4</b>–<b>7</b>) have been carried out. Compounds <b>1</b>–<b>6</b> clearly indicate the existence of a weak antiferromagnetic interaction between the metal ions through the bridging 1,3-bdc and 1,4-bdc ligands. The magnetic properties depend strongly on the nature of the metal center. The luminescence spectra of the complexes have been measured, which indicates a ligand based emission for all seven compounds

Hydrogen Uptake by an Inclined Polycatenated Dynamic Metal–Organic Framework Based Material

A 2D + 2D → 3D inclined polycatenated dynamic metal–organic framework of {[Cu­(4-bpe)­(2-ntp)­(H₂O)₂]·2H₂O}_<i>n</i> [<b>1</b>, where 2-ntp^2– = 2-nitroterephthalate and 4-bpe = 1,2-bis-(4-pyridyl)­ethane] has been synthesized and characterized. The variable-temperature powder X-ray diffraction study indicates the dynamic nature of the inclined polycatenated framework, and the dehydrated framework with exposed metal centers exhibits excellent type I H₂ adsorption of 1.94 wt % at 77 K and 1 bar of pressure

Reversible Phase Transformation in Three Dynamic Mixed-Ligand Metal–Organic Frameworks: Synthesis, Structure, and Sorption Study

Three new dynamic metal–organic frameworks (MOFs) namely {[Cd₂(3,4-pyrdc)₂(4,4′-bipy)­(H₂O)₂]·4H₂O}_<i>n</i> (<b>1</b>), {[Mn₂(3,4-pyrdc)₂(bpee)­(H₂O)₂]·H₂O}_<i>n</i> (<b>2</b>), and {[Cu₂(3,4- pyrdc)₂(bpp)₂(H₂O)₄]·5H₂O}_<i>n</i> (<b>3</b>), based on 3,4-pyridinedicarboxylate (3,4-pyrdc) and three different N,N′-donor ligands [4,4′-bipyridine (4,4′-bipy), 1,2-bis­(4-pyridyl)­ethylene (bpee), and 1,3-bis­(4-pyridyl)-propane (bpp)] with various divalent transition metal ions have been synthesized and characterized by single-crystal and powder X-ray diffraction and other physicochemical methods. In compounds <b>1</b> and <b>2</b>, the 3,4-pyrdc ligand forms two-dimensional (2D) metal–carboxylate sheets that are connected by N,N′-donor ligands to form three-dimensional (3D) structures with water-filled channels. In compound <b>3</b>, the 3,4-pyrdc ligand affords one-dimensional metal–carboxylate chains. These chains are connected by the more flexible bpp ligand to form 2D structures, which are extended to a 3D supramolecular architecture by H-bonding. Compounds <b>1</b> and <b>2</b> show a reversible crystalline-to-crystalline phase transformation upon dehydration and rehydration, whereas compound <b>3</b> exhibits an interesting reversible crystalline-to-amorphous transformation. These transformations have been established and monitored by exhaustive X-ray powder diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis, and morphology studies. The dehydrated forms of <b>1</b>–<b>3</b> selectively adsorb CO₂ over N₂ and also exhibit stepwise water uptake

Sulfonic Group Functionalized Mixed Ligand Coordination Polymers: Synthesis, Characterization, Water Sorption, and Proton Conduction Studies

Five sulfonic acid group functionalized mixed ligand coordination polymers (CPs), namely, {[Zn­(bpeH)­(5-sip)­(H₂O)]·(H₂O)}_<i>n</i> (<b>1</b>), {[Cu­(pyz)­(5-Hsip)­(H₂O)₂]·(H₂O)₂}_<i>n</i> (<b>2</b>), {[Cu­(bpee)_0.5­(5-sip)­(H₂O)₂]·(H₂O)₄­(bpeeH₂)_0.5}_<i>n</i> (<b>3</b>), {[Cu­(bpy)­(5-Hsip)­(H₂O)]·(H₂O)₂}_<i>n</i> (<b>4</b>), and {[Cu­(bpy)₂­(5-H₂sip)₂]·(H₂O)₆}_<i>n</i> (<b>5</b>) [where sip^3– = 5-sulfoiso­phthalate; bpe = 4,4′-bispyridyl­ethane; pyz = pyrazine; bpee = 4,4′-bispyridyl­ethylene; bpy = 4,4′-bipyridine], have been synthesized with varying different N,N′-donor linkers using slow diffusion techniques at room temperature. The CPs possess guest water filled 1D channels and noncoordinating sulfonic acid or coordinated sulfonate groups, which are interconnected by means of extended intermolecular H-bonding interaction, which supports the humidity dependent proton conductivity of the samples. Under 95% relative humidity (% RH), the CPs exhibit the temperature dependent proton conductivity which is maximum up to in the range of ∼10^–5–10^–6 S cm^–1 at 65 °C. In most of the cases, the framework shows activation energies with the value ranging from 0.35 to 0.54 eV, suggesting mostly the contribution of the Grotthuss mechanism of the proton conductivity

Two Series of Isostructural Coordination Polymers with Isomeric Benzenedicarboxylates and Different Azine Based N,N′-Donor Ligands: Syntheses, Characterization and Magnetic Properties

Seven coordination polymers (CPs) with two types of framework structures, namely, {[M­(4-bpdb)­(1,3-bdc)]­·(4-bpdb)_0.5}_<i>n</i> [M = Mn (<b>1</b>), Fe (<b>2</b>), and Co (<b>3</b>)], and {[M­(4-bpdh)­(1,4-bdc)]}_<i>n</i> (M = Mn (<b>4</b>), Fe (<b>5</b>), Co (<b>6</b>), and Cd (<b>7</b>)] have been synthesized through the slow diffusion technique using 1,3-bdc and 1,4-bdc ligands with two different azine based N,N′-donor linkers [1,3-bdc = benzene-1,3-dicarboxylate, 1,4-bdc = benzene-1,4-dicarboxylate, 4-bpdb = <i>N,N</i>′-bis-pyridin-4-ylmethylene-hydrazine and 4-bpdh = <i>N,N</i>′-bis-(1-pyridin-4-yl-ethylidene)-hydrazine]. Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and powder X-ray diffraction (PXRD) analysis. Compounds <b>1</b>–<b>3</b> are isostructural and feature a two-dimensional (2D) framework structure formed by pillaring the one-dimensional [M­(1,3-bdc)]_<i>n</i> double chains through 4-bpdb linkers. In all cases of compounds <b>1</b>–<b>3</b>, free 4-bpdb linkers are present in the lattice and lattice 4-bpdb ligands are involved in π–π and C–H···π interactions with bridging 1,3-bdc and 4-bpdb ligands, to afford three-dimensional (3D) supramolecular structures. Compounds <b>4</b>–<b>7</b> are also isostructural and here the bridging of 1,4-bdc with the divalent metal centers forms a 2D layer of [M­(1,4-bdc)]_<i>n</i> which is further pillared by 4-bpdh to form a 3D pillared-layer framework. Variable temperature magnetic measurements of two sets of isostructural complexes (<b>1</b>–<b>3</b> and <b>4</b>–<b>7</b>) have been carried out. Compounds <b>1</b>–<b>6</b> clearly indicate the existence of a weak antiferromagnetic interaction between the metal ions through the bridging 1,3-bdc and 1,4-bdc ligands. The magnetic properties depend strongly on the nature of the metal center. The luminescence spectra of the complexes have been measured, which indicates a ligand based emission for all seven compounds