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

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

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

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

Set of Multifunctional Azo Functionalized Semiconducting Cd(II)-MOFs Showing Photoswitching Property and Selective CO₂ Adsorption

Syntheses, structural characterizations, photoluminescence, and adsorption properties of three new azo-functionalized Cd­(II)-MOFs, namely, {[Cd­(azbpy)­(msuc)]·2.5­(H₂O)}_<i>n</i> (<b>2</b>), {[Cd­(azbpy)­(mglu)]·5­(H₂O)}_<i>n</i> (<b>3</b>), and {[Cd_1.5(azbpy)₂(glu)]·(NO₃)·MeOH}_<i>n</i> (<b>4</b>) [where msuc²⁻ = methylsuccinate; mglut²⁻ = methylglutarate; glut²⁻ = glutarate; azbpy = 4,4′-azobispyridine] have been reported. The compounds show different structures only with the variation of aliphatic dicarboxylates. The photoswitching behavior for the above-mentioned newly synthesized Cd­(II)-MOFs along with one of our previously reported other azo-functionalized Cd­(II)-MOF, namely, {[Cd­(azbpy)­(suc)]·2­(H₂O)}_<i>n</i> (<b>1</b>), has been studied extensively. At photoilluminated condition, the conductivity values can draw a clear structure–property relationship among the structures of compounds <b>1</b>–<b>4</b>. Single crystal structural analysis reveals that all the compounds exhibit a three-dimensional (3D) framework connected by azbpy linker and respective aliphatic dicarboxylate through their bis-chelating mono/bis oxo-bridging fashion. Compounds <b>1</b>–<b>3</b> exhibit an iso-structural honeycomb like 3D framework showing the same coordination environments, where the metal-carboxylate 2D sheets of compounds <b>1</b>–<b>3</b> are pillared by N,N′-donor azbpy linkers. On the other hand, compound <b>4</b> exhibits a 2-fold interpenetrated 3D framework with a little difference in its coordination environment and the pillaring of 1D metal-carboxylate ladder by azbpy linkers. All the compounds significantly demonstrate their enhanced sensitivity under light rather than the dark condition. The gas and solvent vapor sorption studies have been performed for the synthesized compounds <b>2</b>–<b>4</b>. Moreover, compound <b>2</b> exhibits an enhanced type IV selective CO₂ adsorption isotherm over N₂ along with the appearance of gate opening phenomena in that