Reversible Solid-state Structural Transformations Research Articles

A 2D flexible cobalt-MOF: reversible solid-state structural transformation, two-step and gate-opening adsorption behaviours, and selective adsorption of C2H2 over CO2 and CH4.

A new 2D flexible cobalt(II) framework (Co-MOF) exhibits a reversible solid-state structural transformation upon guest molecule removal/uptake. After activation, Co-MOF-α with 1D porous channels transformed into Co-MOF-β (0D voids) accompanied by a shift in metal and carboxylate coordination modes, the rotation of organic linkers and the contraction of interstitial spaces. Gas adsorption experiments reveal that Co-MOF-β exhibits a two-step CO2 adsorption isotherm and close-to-open (type F-IV) isotherms for C2H2, C2H4 and C2H6 at 195 K. Moreover, it shows typical type I adsorption isotherms for the above gases and the selective uptake of C2H2 over CH4 and CO2 at room temperature.

A reversible photochemical solid-state transformation in an interpenetrated 3D metal-organic framework with mechanical softness.

We synthesized a two-fold interpenetrated 3D MOF with two crystallographically distinct C[double bond, length as m-dash]C bonds, which undergoes [2+2] photo-cycloaddition and thermal reversible reaction, in a single-crystal-to-single-crystal (SCSC) manner. The softer nature and comparable mechanical properties of the crystals of the parent and cyclized MOFs revealed by nanoindentation allowed rationalizing their structural softness and SCSC transformation behaviour.

Syntheses of mono and bimetallic cyamelurate polymers with reversible chromic behaviour.

Ordered coordination polymers (CPs) have been an interesting class of materials for scientific and industrial research for the last few decades. However, their availability as well as certain economic and environmental limitations could slow down their use in many applications. Herein, we present room temperature synthesis in water of a series of CPs (four metal-organic polymers MOPs-(1-4) and three mixed metal-organic polymers MMOPs-(5-7)). All MMOPs were found to be isostructural to MOPs as determined by XRD. Remarkably, MOPs-(2 and 3) and MMOPs-(5-7) exhibit switchable chromic behaviour associated with reversible structural transformation which was facilitated by dehydration/rehydration or solvent exchange (MeOH/H2O) processes. Chromic behaviour and its mechanism were investigated using IR, solid-state UV-Vis, XRD, PXRD and TGA indicating the coordination/de-coordination of water molecules to be the key factor that influences the colour changes. These results render the potential application of MOPs and MMOPs as sensor materials.

Reversible liquid assisted mechanochemical conversion of sodium coordination polymer nanorods to organosilver coordination polymer nanosheets

Reversible solid-state structural transformation of sodium(I) coordination polymer nanorods, prepared by sonochemical procedure, to organosilver coordination polymer nanosheets has been observed upon liquid assisted mechanochemical reaction of compound [Na2(1,5-nds)(H2O)2]n (1), [1,5-H2nds=1,5-naphthalenedisulfonic acid] with AgNO3. During this conversion, two coordinated H2O molecules were removed from 1 and substituted with two carbon atoms from 1,5-nds2− ligand in 2. Thus organosilver coordination polymer of 2 was formed during this conversion and distorted trigonal-bipyramidal coordination geometry in 1 with NaO5 coordination sphere was converted to distorted tetrahedral geometry in 2 (regarding the CC group as one donor) with AgO3C2 coordination sphere.

Reversible structural transformations in a Co(II)-based 2D dynamic metal-organic framework showing selective solvent uptake

A Co(II)-based two-dimensional (2D) metal-organic framework (MOF) [Co(pca)(bdc)0.5(H2O)2] (1) {pca = pyrazine carboxylic acid, and bdc = 1,4-benzene dicarboxylic acid} was synthesized solvothermally. The compound loses the coordinated lattice water molecules on heating which is accompanied by solid-state structural transformation to yield dehydrated phase [Co(pca)(bdc)0.5] (\(\mathbf {1}^{\boldsymbol {\prime }}\)). The hydrated structure can be regained by exposing 1 \(^{\boldsymbol {\prime }}\) to water vapour (1 \(^{\boldsymbol {\prime \prime }}\)). These reversible solid-state structural transformations are accompanied by a visible colour change in the material. The dehydrated compound also shows highly selective water uptake over other solvents like MeOH, EtOH, THF. This selective water uptake can be ascribed to the high affinity of polar water molecule towards the open metal site created on heating. The present report provides important insights into the reversible structural transformations observed due to variable coordination number of the central metal ion and transformability of the framework. The selective water uptake over alcohols along with visible colour change demonstrates the potential of the present compound in bio-alcohol purification. Herein, we report a Co(II)-based 2D dynamic metal-organic framework synthesized under solvothermal conditions. The framework exhibits structural transformation accompanied by a visible colour change owing to the loss of coordinated water. The structure can be regained by selective water uptake over other solvents. The selective water uptake due to flexible framework and visible colour change demonstrates the potential of the present compound for bio-alcohol purification.

Framework-flexibility driven selective sorption of p-xylene over other isomers by a dynamic metal-organic framework.

Chemical separation has great importance in industrial applications. Separation of xylene isomers still prevails to be one of the most important challenges in chemical industry, due to the large amount of commercial use of p-xylene in the production of beverage bottles, fibers and films. A novel Zn(II)-based dynamic coordination framework based on flexible ether-linkage, exhibiting selective adsorption of p-Xylene over its congener C8-alkyl aromatic isomers at ambient conditions is reported. Notably, no dynamic structure based MOF compound is known in the literature which shows clear preference of p-xylene over other isomers. This type of framework-breathing and guest-induced reversible solid-state structural transformations with unique adsorption selectivity can be exploited purposefully to develop smart functional host materials capable of industrially important chemical separations.

Mechanochemical solid state anion-exchange of lead(ii) coordination polymers via an intermediate coordination polymer; new precursors for the preparation of PbBr2/Pb3O2Br2, PbBr(OH) and PbO nanoparticles

The reversible crystal-to-crystal transformations of a 1D lead(II) coordination polymer with the ligand 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), from [Pb(4-bpdh)Br2]n () to intermediate [Pb(4-bpdh)(Br)(NO3)]n () and [Pb(4-bpdh)(NO3)2(H2O)]n () by a solid state anion-replacement processes under mechanochemical reactions, have been studied. The reversible solid state structural transformation of compound to compound and then by anion replacement have been verified by PXRD and IR measurements. PbBr2, PbBr(OH), Pb3O2Br2 and PbO nanoparticles were obtained by the thermal decomposition of compounds , and in oleic acid at 180 °C in an air atmosphere, respectively. These nanoparticles were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM).

Solid state and sonochemical syntheses of nano lead(II) chloride and bromide coordination polymers from its nitrate analog via mechanochemical crystal to crystal transformations

Reversible crystal-to-crystal transformations of 3D lead(II) coordination polymers with the ligand 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), from nitrate analoge [Pb(4-bpdh)(NO3)2(H2O)]n (1) to [Pb(4-bpdh)(NO3)(Br)]n (2), [Pb(4-bpdh)(Br)2]n (3), [Pb(4-bpdh)(NO3)(Cl)]n (4) and [Pb(4-bpdh)(Cl)2]n (5) by solid state anion-replacement processes under mechanochemical reactions, have been studied. The reversible solid state structural transformations of compounds 1–5, by anion-replacement processes under mechanochemical reaction, have been verified by PXRD measurements. Nanoparticles of compounds were synthesized by sonochemical process and characterized by scanning electron microscopy (SEM), powder X-ray diffraction, IR spectroscopy and elemental analyses. The SEM images showed that morphology change occurs during solid state anion-replacements of nanocrystals.

Effect of two sonochemical procedures on achieving to different morphologies of lead(II) coordination polymer nano-structures

Micro and nano-structures of a lead(II) coordination polymer, [Pb2(2-Me-8-Hq)2(MeOH)2]n (1), [2-Me-8-HqH=2-methyl-8-hydroxyquinoline], were synthesized by two sonochemical methods. These new micro and nano-structures were characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Compound 1 was structurally characterized by single-crystal X-ray diffraction and consists of primary dimeric unit of [Pb2(2-Me-8-Hq)2(MeOH)2]. Self assembly between the dimmeric units of [Pb2(2-Me-8-Hq)2(MeOH)2] from Pb-O bonds results in formation of a one-dimensional lead(II) coordination polymer. The PbII-ion in compound 1 has PbO6N1 coordination sphere with a stereo-chemically ‘active’ electron lone pair on the metals. By a reversible solid-state structural transformation, we successfully prepared [Pb2(2-Me-8-Hq)2]n (2) by thermal desolvation of 1. Thermal stability of compound 1 was studied by thermo gravimetric and differential thermal analyses. In addition nano-structure of PbO was prepared from calcination process of compound 1 at 873K.

Solid state structural transformation of 1D to intermediate 2D and then to 3D porous coordination polymer by anion replacement; new precursors for preparation of PbCl2, Pb3O2Cl2 and PbO nanoparticles

A reversible anion exchange of 1D lead(II) coordination polymers with the ligand 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), from [Pb(4-bpdh)Cl2]n (1) to intermediate 2D [Pb(4-bpdh)(Cl)(NO3)]n (2) and then 3D porous coordination polymer [Pb(4-bpdh)(NO3)2(H2O)]n (3) by solid state anion replacement processes under mechanochemical reactions, have been studied. The reversible solid state structural transformations of compound 1 to compound 2 and then 3 by anion replacement have been verified by PXRD and IR spectroscopy. PbCl2, Pb3O2Cl2 and PbO nanoparticles were obtained by thermal decomposition of compounds 1, 2 and 3 in oleic acid as surfactant at 180 °C under an air atmosphere, respectively. These nanoparticles were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM).

Solid- and solution-state structural transformations in flexible lead(ii) supramolecular polymers

Reversible solid-state structural transformations of [Pb2(Q-2-c)2(OAc)2(MeOH)2]n (1) and [Pb2(Q-2-c)2(OAc)2(EtOH)2]n (2) to [Pb2(Q-2-c)2(OAc)2]n (3) have been observed upon thermal desolvation of coordinated MeOH (in 1) and EtOH (in 2) molecules. In addition, irreversible solution-state structural transformations of compounds 1, 2 and 3 to [Pb(Q-2-c)2]n (4) have been observed in H2O. Unlike protic solvents, immersion of 1 and 2 in aprotic solvent results in formation of 3.

Reversible luminescence switching between single and dual emissions of bipyridinium-type organic crystals

An excitation-wavelength-dependent luminescence behavior of a bipyridinium derivative, together with its luminescence switching between single- and dual-emissions upon reversible solid state structural transformation, has been presented.

Reversible solid state structural transformation of a polyhapto lead(ii) polymeric chain to a tetrahapto lead(ii) two-dimensional network by thermal dehydration with no change in nanoplate morphology

A reversible solid state structural transformation of a new 1D lead(II) coordination polymer [Pb(MPOAc)2(H2O)]n (1), (MPOAc−: mono phenyl acetate) involving in situ ligand synthesis with O7Pb⋯C6 coordination sphere to a 2D supramolecular network [Pb(MPOAc)2]n (2) with O6Pb⋯C4 coordination environment has been observed upon heating and dehydration. This change in coordination-mode was confirmed by single-crystal X-ray diffraction analyses of compounds 1 and 2. Thermogravimetric (TG) and differential thermal analyses (DTA) were employed to study the thermal stabilities of compounds 1 and 2. Powder X-ray diffraction experiments showed that the structural transformation occurs in the batch powder samples and lead to monophasic products. Nanoplates of compound 1 were synthesized by a microwave-assisted process and characterized by scanning electron microscopy (SEM), powder X-ray diffraction, IR spectroscopy and elemental analyses. The SEM images showed that no morphology change occurs during this solid state structural transformation.

Reversible Solid-State Structural Transformation of a 1D−2D Coordination Polymer by Thermal De/Rehydration Processes

A new coordination polymer, [Zn(HBTC)(BPE)0.5(H2O)]n·nH2O (1) with an extended 1D ladderlike metal-organic framework (MOF) has been synthesized and structural characterized by single-crystal X-ray diffraction method. Structural determination reveals that, in compound 1, the Zn(II) ion is four-coordinated in a distorted tetrahedral geometry, bonded to one nitrogen atom from one BPE ligand, and three oxygen atoms from two monodentate carboxylate groups of two HBTC(2-) ligands and one coordinated water molecule. The HBTC(2-) acts as a bridging ligand with a bis-monodentate coordination mode, connecting the Zn(II) ions to form a one-dimensional (1D) [Zn(HBTC)] chain. Two 1D chains are then interlinked via the connectivity between the Zn(II) ions and anti-BPE liagnds to complete the 1D ladderlike MOF. Adjacent 1D Ladders are further extended to a 2D hydrogen-bonded layered network through the intermolecular O-H · · · O hydrogen bond between the carboxylic group and carboxylate group of interladder HBTC(2-) ligand. Adjacent 2D layers are then packed orderly in an ABAB-type array via the intermolecular interactions of combined π-π interaction and O-H · · · O hydrogen bonds to form a 3D supramolecular architecture exhibiting 1D channels intercalated with guest water molecules. The reversible solid-state structural transformation between crystalline 1 with 1D ladderlike framework and its dehydrated powder 2, [Zn(HBTC)(BPE)0.5]n, with 2D framework via the displacement of coordinated water molecule to HBTC(2-) ligand, by thermal de/rehydrated processes has been verified by PXRD measurements. The emission of 1 and 2 is ascribed to a ligand-based transition.