Single-crystal To Single-crystal Transformation Research Articles

Single Crystal to Single Crystal Transformation of Porous Materials based on Zinc Nodes and Mercaptobenzoic Acid.

Porous coordination polymers (PCPs) are an excellent class of porous crystalline materials with tunable properties and intriguing potential applications spanning multiple disciplines. In this work, we report the synthesis and characterization of a PCP (HI-103) based on 4,4'-dithiodibenzoic acid ligand and zinc nitrate with two DMF molecules residing in the porous network. The stability of the porous network was analyzed by heating the compound at 60.0 °C for two days, and the structural analysis revealed a new PCP (HI-104) was formed with one of the DMF molecules, indicating a single-crystal to single-crystal (SCSC) transformation. The solvent molecules were completely removed by extensive drying (HI-103-dry), and the integrity of the porous network was verified by powder X-ray diffraction (PXRD) and thermogravimetric analysis. The reversibility of SCSC transformation was confirmed by treating HI-103-dry with DMF molecules, resulting in HI-103 after five days. The adsorption studies of HI-103-dry with other solvents revealed that SCSC transformation was not observed for DMA and DEA, but some structural changes were observed in the presence of DMSO. The adsorption studies performed in the presence of an equimolar mixture of DMF, DMA, and DMA indicated that HI-103-dry could selectively adsorb DMF molecules from the analogous mixture.

Dehydration-triggered structural phase transition-associated ferroelectricity in a hybrid perovskite-type crystal

Since the appearance of Rochelle salt, ferroelectrics have received extensive attention from researchers due to they are playing an important role in sensors, memories, mechanical actuation, and so on. In recent years, with the rapid development of molecular ferroelectrics, high-performance molecular ferroelectrics have become effective complement to inorganic ferroelectrics. However, compared with inorganic ferroelectrics, the family of molecular ferroelectrics is relatively scarce, and exploring high-performance ferroelectric materials through new synthesis strategies has become the trend of molecular ferroelectrics. Here, we successfully transformed non-polar material 1 (2-H2PCA)2(H2O)CdCl6 (2-H2PCA = 2-picolylamine cation) into polar material 2 (2-H2PCA)2CdCl6 by single-crystal to single-crystal transformation (SCSCT). Meanwhile, 2 exhibits clear ferroelectricity with a high-temperature Tc of 378 K, a Ps of 1.18 μC cm−2 at 300 K. This work not only realizes the purpose of synthesizing ferroelectrics by forming polar structures by SCSCT, but also realizes the reversibility of SCSCT, which provides ideas for the construction and exploration of new molecular ferroelectrics.

Photoinduced Single-Crystal to Single-Crystal Transformation via Conformational Change with Turn-On Fluorescence

Single-crystal to single-crystal (SCSC) transformation by phototrigger is presently attracting immense research interest in many fields such as sensors, actuators, artificial muscles, soft robotics, and energy harvesting. However, the only success of rare examples has been achieved by SCSC transformation so far, involving a change in molecular composition based on photocyclization reactions. Here, we show photoinduced SCSC transformation of 3-methylene-2-(quinolin-8-yl) isoindolin-1-one (MQIO) derivatives from monoclinic to triclinic phase via conformational change, just as “small input and big output”. UV light induces a molecular conformation change of MQIO-H with rotation (11.3°) of the carbon–nitrogen single bond. The conformational changes of MQIO-H lead to the slides of molecular packing in crystals, finally resulting in the SCSC transformation from the monoclinic to the triclinic phase. In addition, the SCSC transformation was accompanied by turn-on fluorescence and shape changes of single crystal. The shape changes of single crystals can be clearly observed by UV light triggering under an optical microscope. This work provides a strategy to achieve SCSC transformation via photoinduction.

Water Molecule-Induced Reversible Magnetic Switching in a Bis-Terpyridine Cobalt(II) Complex Exhibiting Coexistence of Spin Crossover and Orbital Transition Behaviors.

The development of molecule-based switchable materials remains an important challenge in the field of molecular science. Achievement of a structural phase transition induced by adsorption/desorption of guest molecules in spin crossover (SCO) Co(II) compounds is of significant interest because of the possibility that the spin state of the magnetic anisotropic high-spin (HS, S = 3/2) and low-spin (LS, S = 1/2) states can be switched via the induced changes in associated intermolecular interactions. In this study, we demonstrated a reversible magnetic switching associated with spin state conversion, along with a single-crystal to single-crystal (SCSC) phase transition induced by dehydration/rehydration. [Co(terpy)2](BF4)2·H2O (1·H2O; terpy = 2,2':6',2''-terpyridine) assembles in the solid state via π-π and CH-π interactions involving adjacent terpyridine cores along the ab direction to form two-dimensional (2D) layered domains. 1·H2O exhibits gradual and incomplete SCO, from fully HS to ca. 0.5 HS, and the field-induced single-molecule magnet (SMM) behavior attributed to the presence of the anisotropic partial high-spin Co(II) species. 1·H2O undergoes a SCSC transformation accompanied by a change from the tetragonal space group I41/a to P42/n via a dehydration process. Dehydrated 1 exhibits a reverse thermal hysteresis behavior (T1/2↑ = 287 K; T1/2↓ = 270 K) in the gradual SCO region from fully HS to ca. 0.5 HS, followed by an ordinary thermal hysteresis (T'1/2↑ = 195 K; T'1/2↓ = 155 K) to fully LS Co(II). A temperature-dependent single-crystal X-ray structural analysis revealed that the reverse hysteresis can be attributed to an order/disorder structural phase transition of the BF4- anions involving a symmetry breaking to yield the monoclinic space group P21/n and orbital (angular momentum) transition (LT). Both the SCSC phase transition and magnetic behavior are switchable by dehydration/rehydration processes; thus 1 again adsorbs water at room temperature to give both the original structure and its magnetic behavior.

Ion exchange collaborating coordination substitution: More efficient Cr(VI) removal performance of a water-stable CuII-MOF material

An unusual water-stable cationic metal-organic framework {[Cu(L)0.5(bpe)(H2O)](NO3)•(H2O)0.5}n (1) (H4L = bis(3,5-dicarboxypyridinium)-p-xylylene) was synthesized, which was developed into an effective capture material for removal chromate from water. The results show that this material efficiently traps HCrO4- pollutant ions via single-crystal to single-crystal (SCSC) coordination substitution process. The HCrO4- uptake capacity of 1 is high to 190 mg/g. Meaningfully, the structure of 1-HCrO4 ({[Cu(L)0.5(bpe)(HCrO4)]}n) can be accurately obtained by single-crystal X-ray diffraction, where the chromate enter the framework to form stable coordination with central metal ions Cu2+. This is the first example of a stable coordination between chromate and the framework during the capture process. The captured HCrO4- are not dissociated easily into the solution due to the coordination bond. This interaction makes the enrichment of HCrO4- more stable and the capture capacity excellent. Furthermore, the HCrO4- releasing process displays good regeneration in a single crystal state, which further elaborates the reversible SCSC transformation. The mechanism of Cr(VI) removal was also confirmed by DFT calculation studies. This work provides a new way to design and develop efficient MOF capture materials.

Unveiling the Mechanism of Water‐Triggered Diplex Transformation and Correlating the Changes in Structures and Separation Properties

Recently, great attention has been devoted to the initial and final structures of single‐crystal to single‐crystal (SCSC) transformations and dissolution‐recrystallization structural transformations (DRSTs), whereas the isolation and characterization of crucial intermediates and the unequivocal mechanism of the dynamic conversion process receive comparatively little consideration. Herein, a CuII‐based porous coordination polymer (PCP), which possesses a Kagomé lattice, is solvothermally synthesized. Triggered by water, the 2D Kagomé lattice (PCP‐1) primarily undergoes a reversible SCSC transformation to a distorted Kagomé intermediate (PCP‐2), which is followed by a DRST process to form a 3D NbO framework (PCP‐3) in situ. To the best of our knowledge, this is the first demonstration of a mixed SCSC and DRST transformation process. Notably, the sequential transformations result in the formation of the intermediate and the final product, which could not be obtained by direct synthesis. Regarding the intermediate, we have characterized the transformation separately and propose a plausible mechanism. More interestingly, the adsorption isotherms of water, methanol, and ethanol for the activated materials are distinctly different from one another. PCP‐2′ can uptake all three vapors with different adsorption capacities; however, the 3D transformed material PCP‐3′ only significantly absorbs water, which is concomitant with an amorphous‐to‐crystalline transformation, leading to the selective extraction of water from alcohol.

Anion-exchange and anthracene-encapsulation within copper(II) and manganese(II)-triazole metal-organic confined space in a single crystal-to-single crystal transformation fashion.

A new multidentate ligand 1-(9-(1H-1,2,4-triazol-1-yl)anthracen-10-yl)-1H-1,2,4-triazole (tatrz) was designed and synthesized. Using tatrz as a building block, three novel coordination frameworks, namely, {[Cu(tatrz)2(NO3)2]·(CH3OH)·4H2O}n (1), {[Cu(tatrz)2(H2O)2](BF4)2}n (2), and [Mn(tatrz)2(SCN)2(CH3OH)]·2H2O (3) can be isolated. Anion-exchange experiment indicates that NO3(-) anions in the two-dimensional (2D) copper framework of 1 can be completely exchanged by ClO4(-) in an irreversible single crystal-to-single crystal (SC-SC) transformation fashion, as evidenced by the anion-exchange products of {[Cu(tatrz)2(H2O)2](ClO4)2·4CH3OH} (1a). Further, if 1a was employed as a precursor in N,N-dimethylformamide (DMF), an isomorphic solvate of {[Cu(tatrz)2(DMF)2](ClO4)2·2H2O}n (1b) can be generated during the reversible dynamic transformation process. When 1 was immersed in CH3OH, a distinct 2D layer {[Cu(tatrz)2(NO3)2]·4.4CH3OH·0.6H2O}n (1c) was isolated. Interestingly, the solvent-exchange conversion is also invertible between 1 and 1c, which exhibits spongelike dynamic behavior with retention of crystalline integrity. If the 2-fold interpenetrating three-dimensional (3D) framework 2 is selected, it can be transformed into another 2-fold interpenetrating 3D framework {[Cu(tatrz)2(H2O)2](ClO4)2·5.56H2O}n (2a) in a reversible SC-SC transformation fashion. However, when the light yellow crystals of mononuclear complex 3 were exposed to trichloromethane containing aromatic organic anthracene (atan), through our careful observation, the crystals of 3 were dissolved and reassembled into dark brown crystals of 2D crystalline coordination framework {[Mn(tatrz)2(SCN)2]·(atan)}n (3a). X-ray diffraction revealed that in 3a, atan acting as an organic template was encapsulated in the confined space of the 2D grid. Luminescent measurements illustrate that 3a is the first report of multidimensional polymers based on triazole derivatives as luminescent probes of Mg(2+).

Water molecule-driven reversible single-crystal to single-crystal transformation of a multi-metallic coordination polymer with controllable metal ion movement

A single-crystal to single-crystal (SC-SC) transformation process driven by water molecules has been exhibited by a multi-metallic coordination polymer. The in situ heating single crystal X-ray diffraction technique was applied to study the control of metal ion movement in the reversible SC-SC transformation process.

Metal-organic frameworks displaying single crystal-to-single crystal transformation through postsynthetic uptake of metal clusters

Three metal-organic frameworks (MOFs) formulated as [Co3O(BTB)2(H2O)x(DMF)y]·zDMF·nH2O (BTB = 1,3,5-benzenetribenzoate; 1a, x = y = 1, z = 7.5, n = 12; 1b, x = 2, y = 0, z = 8.5, n = 8; 1c, x = 2, y = 1, z = 7, n = 8) have been synthesized under different temperatures; they crystallize as two-fold interpenetrated analogous structures with the same structural trinuclear Co3O(CO2)6 secondary building units (SBUs), and their stabilities depend on the temperature under which they formed. Upon immersion in the filtrate of 1a (namely 1a-s, freshly filtered) or 1b (namely 1b-s, filtered and then activated in air for three days), single crystal-to-single crystal (SCSC) transformations of 1a–1c to a new MOF, formulated as [Co6O2(OH)4(BTB)8/3(H2O)4]·14DMF·4EtOH·2H2O (2), occur along with dramatic color change from blue purple to red. Crystallographic studies reveal that the new MOF is also two-fold interpenetrated but is constructed with hexanuclear Co6O2(CO2)8 SBUs. This SCSC transformation from 1a–1c to 2 can take place only in 1a-s or 1b-s but not in 1c-s and is accompanied with an increase of metal-to-ligand ratio. ESI-MS studies unveil the formation of free {Co3O} units in situ formed only in 1a-s and 1b-s, and evidence that the SCSC transformation involves a postsynthetic uptake of free metal clusters, {Co3O}. On the other hand, the SCSC transformation speed decreases from 1a to 1c, which is determined by the chelate carboxylate groups undergoing cleavage of metal-carboxylate bonds during the SCSC transformation and the shape of the 1D channels affecting the diffusion of free metal clusters. Furthermore, the resulting MOF (2) can maintain its crystallinity upon activation and adsorbs iodine up to 38 wt%. Combined with the significant SCSC transformation through postsynthetic uptake of free metal clusters and the resulting MOF capable of adsorbing iodine, the present approach not only provides a true route to construct SBUs-based MOF materials with pre-existing “real” SBUs but also represent a new type of SCSC transformation in the field of MOFs that is able to efficiently tune structures and physicochemical properties of MOFs in the solid states.

A Dynamic Open Framework Exhibiting Guest- and/or Temperature-Induced Bicycle-Pedal Motion in Single-Crystal to Single-Crystal Transformation

A ligand bis(4-imidazol-1-yl-phenyl)diazene (azim) incorporating an azo moiety at the center and two imidazole groups at the terminals forms two coordination polymers {[Co(azim)(2)(DMF)(2)]·(ClO(4))(2)·2DMF}(n) (1) and {[Cd(azim)(2)(DMF)(2)]·(ClO(4))(2)·2DMF}(n) (2) (DMF = N,N'-dimethylformamide) at room temperature. Both 1 and 2 are isostructural with rhombic two-dimensional sheets stacking in ABAB... fashion resulting in large voids that contain DMF and ClO(4)¯ as guests. In 1, the azo groups and phenyl rings are disordered over two positions and as in usual cases, the pedal motion cannot be discerned. Upon heating, 1 turns amorphous. In the case of 2, however, heat treatment does not lead to loss of crystallinity. Thus, when a crystal of 2 (mother crystal) is heated slowly, it causes substantial movement or escape of both metal-bound and lattice DMF besides movement of ClO(4)¯ anions to give daughter crystals 2a, 2b, and 2c without losing crystallinity (single-crystal to single-crystal (SC-SC) transformation). Most interestingly, the X-ray structures of 2 and its daughter products reveal stepwise reversible bicycle-pedal or crankshaft motion of the azo group. When a crystal of 2c is kept in DMF for 10 h, crystal 2' is formed whose structure is similar to that of 2 with slight changes in the bond distances and angles. Also, crystals of 2 are converted to 3 and 4 upon being kept in acetone or DEF (DEF = N,N'-diethylformamide), respectively, for 10 h at ambient temperature in SC-SC transformation. In 3, each lattice DMF molecule is replaced by an acetone molecule, leaving the two coordinated DMF molecules intact. However, in 4, all lattice and coordinated DMF molecules are replaced by equal number of DEF molecules. Both in 3 and 4, the azo moieties show bicycle-pedal motion. Thus, bicycle-pedal motion that normally cannot be observed is shown here to be triggered by heat as well as guest molecules in SC-SC fashion.

Diamondoid Three-Dimensional Metal-Organic Framework Showing Structural Transformation with Guest Molecules

The potential of carboxylate and imidazole-based mixed ligands for forming metal organic frameworks (MOFs) is demonstrated with 4-(1H-imidazole-1-yl)benzoic acid (HIBA) to generate a flexible material. Reaction of HIBA with Cd(NO3)2·6H2O under solvothermal condition in N,N-dimethylformamide (DMF), produces a three-dimensional MOF, {[Cd(IBA)2].2DMF}n (1⊃2DMF), which on heating at 60 and 200 °C turns opaque, forming {[Cd(IBA)2]·DMF}n (1⊃DMF) and {[Cd(IBA)2]}n (1), respectively, as characterized by PXRD, TGA, and elemental analysis. Either of these compounds on keeping in dry DMF for 15 days affords the original compound, i.e., showing reversibility deduced from PXRD. When a crystal of 1⊃2DMF is immersed in moist N,N-diethylformamide (DEF) in a vial open to atmosphere, a new compound, {[Cd(IBA)2]·DEF·H2O}n, (2) is formed in 1 month in a single-crystal to single-crystal (SC-SC) fashion. Also, a crystal of 1⊃2DMF on immersing in moist DMF produces another interesting 3D framework {[Cd(IBA)2.H2O]·DMF·3H2O}n, (3) in a SC-SC transformation. These coordination polymers show interesting 4-fold interpenetrating diamondoid 3D network structures.

Vapor-Diffusion-Mediated Single Crystal-to-Single Crystal Transformation of a Discrete Dimeric Copper(II) Complex to a Discrete Tetrameric Copper(II) Complex

The symmetric dimeric complex [Cu(mu(2)-hep)(TFA)(H(2)O)](2) (1) has been synthesized from 2-(2-hydroxyethyl)pyridine (hep-H), trifluoroacetic acid (TFA-H), and copper acetate in a 95:5 (v/v) MeOH-H(2)O mixture at 298 K. Each Cu(II) ion in 1 is linked with two mu(2)-alcoholic oxygen atoms and one pyridine nitrogen atom of hep, and the other two coordination sites are occupied by the oxygen donors of TFA and H(2)O. At room temperature, the blue single crystals of 1 transform to the green single crystals of a tetrameric complex, [Cu(4)(mu(3)-hep)(2)(mu(2)-hep)(2)(mu(2)-TFA)(2)(TFA)(2)] (2), in presence of alcoholic vapor. The facile single crystal-to-single crystal (SCSC) transformation of 1 to 2 is accompanied by the removal of coordinated H(2)O molecules in 1 and concomitant formation of four new covalent bonds, two Cu-O(mu(3)-hep) and two Cu-O(mu(2)-TFA). The SCSC transformation of 1 to 2 is selective to the alcoholic vapor; the exposure of single crystals of 1 to heat or light or in vacuum has resulted in an immediate loss in crystallinity.