SCSC Transformation Research Articles

Desolvation–Solvation-Induced Reversible On–Off Switching of Two Memory Channels in a Cobalt(II) Coordination Polymer: Overlay of Spin Crossover and Structural Phase Transition

Desolvation–Solvation-Induced Reversible On–Off Switching of Two Memory Channels in a Cobalt(II) Coordination Polymer: Overlay of Spin Crossover and Structural Phase Transition

Ultrafast Single-Crystal-to-Single-Crystal Transformation from Metal-Organic Framework to 2D Hydroxide.

Single-crystal-to-single-crystal (SCSC) transformations have received considerable interest in crystal engineering, owing to providing a key platform for creating new materials. However, because of the limited tolerance of chemical bonds against the lattice strains, it is challenging to maintain the crystallinity when the structure changes dramatically. Here, a peculiar SCSC transformation from organic crystals to inorganic crystals, simultaneously achieving a drastic change in structure, connectivity, and dimension, is reported. As a demonstration, after reacting with liquid gallium, zeolitic imidazolate framework-8 (ZIF-8) can easily transform to 2D hydroxide single crystals. Interestingly, long-range ordered metallic atoms of hydroxide inherited from the ordered atomic arrangement of ZIF-8, but the connectivity is distinct. With good universality and extensibility, this transformation vastly expands the research scope of the SCSC transformations and provides a novel pathway for the synthesis of crystalline materials.

Single-Crystal-to-Single-Crystal Transformation and Catalytic Properties of New Hybrid Perhalidometallates

Two new organic–inorganic salts of perhalidometallates with protonated organic amine cations have been synthesized and characterized by X-ray diffraction and thermal analysis. (CHBMAH2)ZnBr4·3/2H2O 1 and (CHBMAH2)ZnCl4 4 [(CHBMAH2)2+: 1,3-cyclohexanebis(methylammonium)] were obtained in single-crystal form. The crystal packing in all of the obtained compounds is governed by the formation of various non-covalent intermolecular forces between tetrahalidometallate anions and organic cations, assisted by water molecules in the hydrates. Hirshfeld surface analysis denotes that the most important contributions to the crystal packing are X···H/H···X (X: Cl, Br, I) and H···H interactions. Interestingly, the compound 1,3-cyclohexanebis(methylammonium)tetrachloridozincate (II) dihydrate, (CHBMAH2)ZnCl4·2H2O 2, undergoes thermally-triggered single-crystal-to-single-crystal (SCSC) transformation upon dehydration to produce a supramolecular solid compound, 1,3-cyclohexanebis(methylammonium) tetrachloridozincate (II), (CHBMAH2)ZnCl4 4. The SCSC transformation causes changes in the lattice parameters and a structural rearrangement. Furthermore, the catalytic properties of (CHBMAH2)ZnCl4·2H2O 2 and (CHBMAH2)CdI4·2H2O 3 have been explored in the acetalization process using various uncommon alcohols, beyond methanol or ethanol, for the first time in the literature, with outstanding results, and opening the door to the formation of alternative acetals.

Joint Experimental and Theoretical Studies of Two Cu(II) Complexes with a 1,2,3-Triazole Derivative as Ligand: SCSC Transformation and Tunable Magnetic Properties

The two new mononuclear complexes Cu(tdp)Cl2·MeCN (1·MeCN, tdp = 2,2′-(1H-1,2,3-triazole-1,4-diyl)dipyridine) and Cu(tdp)Cl2 (1) have been synthesized. Each compound can undergo a reversible SCSC t...

Single-crystal-to-single-crystal transformations among three Mn-MOFs containing different water molecules induced by reaction time: crystal structures and proton conductivities.

Three Mn-MOFs {[Mn3(μ4-L)2(H2O)7]·4H2O}n (1), {[Mn3(μ5-L)2(H2O)6]·4H2O}n (2) and {[Mn3(μ7-L)2(H2O)2]}n (3) (H3L = 5-(6-carboxypyridin-3-yl)isophthalic acid) were obtained under different reaction times and temperatures. Interestingly, induced by reaction time, compound 1 can lose one water molecule and SC-SC transform into compound 2. Similarly, compound 2 can also SC-SC transform into 3. Studies on two SC-SC transformation processes were carried out and the transformation mechanisms were deduced, which were verified by TG analyses. Different numbers of water molecules in the three compounds resulted in different coordination environments of the metal cation, coordination modes of the L3- ligand, continuities of hydrogen bonds, dimensions of framework and porosities. The AC impendence spectra studies revealed that compounds 1-3 can enhance the proton conductivities of the Nafion composite membrane to about 47.77%, 36.88% and 21.28%, respectively. It is speculated that the highest proton conductivity of compound 1 may be due to its continuous hydrogen bond chain and highest water uptake, which were mainly decided by the number of water molecules.

A cationic thorium-organic framework with triple single-crystal-to-single-crystal transformation peculiarities for ultrasensitive anion recognition.

Single-crystal-to-single-crystal transformation of metal–organic frameworks has been met with great interest, as it allows for the creation of new materials in a stepwise manner and direct visualization of structural transitions when subjected to external stimuli. However, it remains a peculiarity among numerous metal–organic frameworks, particularly for the ones constructed from tetravalent metal cations. Herein, we present a cationic thorium–organic framework displaying unprecedented triple single-crystal-to-single-crystal transformations in organic solvents, water, and NaIO3 solution. Notably, both the interpenetration conversion and topological change driven by the SC–SC transformation have remained elusive for thorium–organic frameworks. Moreover, the single-crystal-to-single-crystal transition in NaIO3 solution can efficiently and selectively turn the ligand-based emission off, leading to the lowest limit of detection (0.107 μg kg−1) of iodate, one of the primary species of long-lived fission product 129I in aqueous medium, among all luminescent sensors.

Single-crystal-to-single-crystal transformation of tetrathiafulvalene-based hydrogen-bonded organic frameworks

A TTF-based HOF undergoes SCSC transformation into another two isomers in different solvents.

Flexible Luminescent MOF: Trapping of Less Stable Conformation of Rotational Isomers, In Situ Guest-Responsive Turn-Off and Turn-On Luminescence and Mechanistic Study.

Flexible and dynamic CuI metal-organic framework [Cu(I)-MOF (1)] with well-defined nanoporous channel built with flexible terpyridine ligand offers a scaffold for the inclusion of different classes of guest molecules through a single-crystal-to-single-crystal (SCSC) transformation in the vapor phase at ambient conditions with visual color change. Thus, Cu(I)-MOF (1) offers a potential platform for molecular recognition and undergoes guest-responsive structural dynamism that can be triggered by interfacial interactions. Despite having the stable conformation of the rotational isomers, it selectively encapsulates the less stable conformation (eclipsed and gauche) into its cavity from their vapor phases in the SCSC process. All of the guest-exchanged processes are reversible. It shows selectivity toward less polar guest in a class. The intermediate of all of the guest-exchanged processes appeared as a black material (H2O@Cu(I)-MOF) (1z) prior to the encapsulation of each guest that happens through the SCSC manner followed by encapsulation of the guests replacing H2O in situ at ambient conditions through SCSC transformation. This confirms that the process is a two-step process leading to a common intermediate. The MOF loses its luminescence behavior with H2O removing lattice solvents in situ and appears as a black material, and it regains its luminescence property with the guests replacing H2O. Thus, the MOF displays both luminescence "turn-off" and "turn-on" before and after incorporation of the guests, respectively, leading to a common turn-off mechanism. A fluorescence titration experiment shows selectivity toward aniline among benzene and its derivatives.

Solvent-triggered single-crystal-to-single-crystal transformation from a monomeric to polymeric copper(II) complex based on an aza macrocyclic ligand.

Reversible solvent-triggered single-crystal-to-single-crystal (SCSC) transformations are observed between two copper(II) azamacrocyclic complexes: [Cu(C16H38N6)(H2O)2](C12H6O4) (1) and [Cu(C16H38N6)(C12H6O4)] (2). Complex (1) was prepared via self-assembly of a copper(II) azamacrocyclic complex containing butyl pendant groups, [Cu(C16H38N6)(ClO4)2], with 2,7-naphthalenedicarboxylic acid. When monomeric compound (1) was immersed in CH3OH, coordination polymer (2) was obtained, indicating a solvent-triggered SCSC transformation. Furthermore, when (2) was immersed in water, an reverse SCSC transformation from (2) to (1) occurred. Complex (1) presents a 3D supramolecular structure formed via intermolecular hydrogen-bonding interactions, whereas complex (2) features a 1D zigzag coordination polymer. The reversible SCSC transformation of (1) and (2) was characterized using single-crystal X-ray diffraction and in situ powder X-ray diffraction techniques. Despite its poor porosity, complex (2) displayed interesting CO2 adsorption behaviour under CO2 gas.

Step-by-step: uncommon SCSC transformation accompanied by stepwise change in the binding of a particular ligand within a mononuclear complex upon stepwise desolvation

Uncommon SCSC transformation when desolvation induces subtle changes within a mononuclear complex, namely a stepwise change in the binding of a particular ligand.

Purely inorganic frameworks based on polyoxometalate clusters with abundant phosphate groups: single-crystal to single-crystal structural transformation and remarkable proton conduction.

A pure-inorganic framework based on {P4MoV4MoVI2} clusters with rich phosphate groups has been synthesized. It underwent a single crystal to single crystal conversion in air to form a new framework with changes both in the metal valent state and coordination environment. The new framework exhibits an ultra-high proton conductivity of 1.33 × 10-2 S cm-1 at 95 °C and 98% relative humidity and excellent stability.

Single-crystal-to-single-crystal transformation and proton conductivity of three hydrogen-bonded organic frameworks.

We report the cyclic single-crystal-to-single-crystal transformation of three hydrogen-bonded organic frameworks (HOFs), induced by the change of temperature and humidity, which clearly reveals that the -SO3-and -NH2 groups in UPC-H7 and UPC-H8 facilitate the diffusion of water molecules into their anhydrous structures to form hydrous UPC-H9. Their proton conductivity was studied under different humidity at varying temperature, showing that the proton conductivity is closely related to water molecules entering the crystal structures arising from the hydrogen bonded reorganization in combination with the triaxial single-crystal proton conductivity tests.

Exploiting Aurophilic Interactions in a [2 + 2] Photocycloaddition: Single-Crystal Reactivity with Changes to Surface Morphology

A single-crystal-to-single-crystal (SCSC) photodimerization is achieved using Au(I) coordination and aurophilic interactions. The rigid Au2(dppbz)(CF3COO)2 precursor (dppbz = 1,2-bis(diphenylphosphino)benzene) self-assembles with 1,2-trans-bis(4-pyridyl)ethylene (bpe) to afford a discrete [Au4(dppbz)2(bpe)2]4+ macrocycle in the solid state. The alkene undergoes a [2 + 2] photocycloaddition reaction. The photoreaction proceeds via a rare SCSC transformation in quantitative yield that generates [Au4(dppbz)2(4,4'-tpcb)]4+ (4,4'-tpcb = rctt-tetrakis(4-pyridyl)cyclobutane) stereoselectively. Mechanical strain induced by the photoreaction is evidenced by the formation of ramp features on single-crystal surfaces using scanning electron microscopy.

Single-Crystal-to-Single-Crystal Transformation of Hydrogen-Bonded Triple-Stranded Ladder Coordination Polymer via Photodimerization Reaction.

A one-dimensional hydrogen-bonded triple-stranded ladder coordination polymer [Cd(bpe)1.5(NO3)2(H2O)] (1) (where bpe = trans-1,2-bis(4-pyridyl)ethylene) containing three parallel C═C double bonds was synthesized. This compound undergoes photochemical [2 + 2] cycloaddition and produces rctt-tetrakis(4-pyridyl)cyclobutane (rctt-tpcb) in up to 67% yield via Single-Crystal-to-Single-Crystal (SCSC) transformation. Triple-stranded ladder-like structures have never before displayed such a kind of SCSC transformation. Furthermore, photoirradiation of ground 1 produces rctt-tpcb in up to 100% yield in the solid state. On the basis of the alignment of three C═C olefinic bonds of bpe ligands in parallel, only two out of the three aligned bpe are expected to undergo [2 + 2] photodimerization. However, the quantitative yield from the solid-state photochemical [2 + 2] cycloaddition reaction has been achieved via grinding of crystals of 1 to a powder. The effects of grinding on photoreactivity of 1 were thoroughly studied using 1H NMR spectroscopy, thermogravimetric analysis (TGA), and Raman spectroscopy. These studies indicate that the molecular movements of the hydrogen-bonded ladders are reinforced due to the loss of coordinated water molecules and the further crystal repacking via bond-breaking/forming of the hydrogen-bonded assemblies during mechanical grinding. The 100% photodimerization of ground 1 shows that the grinding accelerates internal molecular motions of ladder structures within the crystals lattice. The solid-state photoluminescence of 1, before and after UV irradiation, was investigated at room temperature, both indicative of interesting luminescent properties.

Adsorption behaviour of a CdII-triazole MOF for butan-2-one in a single-crystal-to-single-crystal (SCSC) fashion: the role of hydrogen bonding and C-H...π interactions.

The adsorption behaviour of the CdII-MOF {[Cd(L)2(ClO4)2]·H2O (1), where L is 4-amino-3,5-bis[3-(pyridin-4-yl)phenyl]-1,2,4-triazole, for butan-2-one was investigated in a single-crystal-to-single-crystal (SCSC) fashion. A new host-guest system that encapsulated butan-2-one molecules, namely poly[[bis{μ3-4-amino-3,5-bis[3-(pyridin-4-yl)phenyl]-1,2,4-triazole}cadmium(II)] bis(perchlorate) butanone sesquisolvate], {[Cd(C24H18N6)2](ClO4)2·1.5C4H8O}n, denoted C4H8O@Cd-MOF (2), was obtained via an SCSC transformation. MOF 2 crystallizes in the tetragonal space group P43212. The specific binding sites for butan-2-one in the host were determined by single-crystal X-ray diffraction studies. N-H...O and C-H...O hydrogen-bonding interactions and C-H...π interactions between the framework, ClO4- anions and guest molecules co-operatively bind 1.5 butan-2-one molecules within the channels. The adsorption behaviour was further evidenced by 1H NMR, IR, TGA and powder X-ray diffraction experiments, which are consistent with the single-crystal X-ray analysis. A 1H NMR experiment demonstrates that the supramolecular interactions between the framework, ClO4- anions and guest molecules in MOF 2 lead to a high butan-2-one uptake in the channel.

Temperature-Induced Single-Crystal-to-Single-Crystal Transformations with Consequential Changes in the Magnetic Properties of Fe(III) Complexes.

The present article deals with an one-to-one structure–property correspondence of a dinuclear iron complex, [Dipic(H2O)FeOH]2·H2O (1) (Dipic = pyridine-2,6-dicarboxylic acid). Variable-temperature X-ray single-crystal structural analysis confirms a phase transition of complex 1 to complex 2 ([Dipic(H2O)FeOH]2) at 120 °C. Further, single-crystal-to-single-crystal (SCSC) transformation was monitored by temperature-dependent single crystal X-ray diffraction, powder X-ray diffraction, time-dependent Fourier-transform infrared spectroscopy, and differential scanning calorimetry. SCSC transformation brings the change in space group of single crystal. Complex 1 crystallizes in the C2/c space group, whereas complex 2 crystallizes in the Pi̅ space group. SCSC transformation brings the change in packing diagram as well. Complex 1 shows two-dimensional network through H-bonding, whereas the packing diagram of complex 2 shows a zigzag-like arrangement. Phase transformation not only fetches structural changes but also in the magnetic properties. Difference in Fe–O–Fe bond angles of two complexes creates notable variation in their antiferromagnetic interactions with adjacent metal centers.

Temperature-Controlled Degree of Interpenetration in a Single-Crystal-to-Single-Crystal Transformation within Two Co(II)-Triazole Frameworks.

Four-fold interpenetrating framework 1a can be constructed driven by temperature-controlled SC-SC transformation from 2-fold interpenetrating network 1. Luminescent properties indicated that 1a can be viewed as a luminescent sensor of high-explosives.

A Zn(II)-based 1D coordination polymer: Temperature-induced SCSC transformation and selective sorption of Congo Red

Solvothermal reaction of Zn(NO3)2·6H2O with 1,4-bis(2-(pyridin-4-yl)vinyl)benzene (1,4-bpeb) and 1,3,5-benzenetricarboxylic acid (1,3,5-H3BTC) (molar ratio = 1:1:3) at 120 °C in CH3CN/H2O (v/v = 1:2) produced a one-dimensional (1D) coordination polymer {[1,4-bpebH2][Zn(H2O)(1,3,5-HBTC)(μ-1,3,5-HBTC)]·2H2O}n (1; [1,4-bpebH2]2+ = 4,4′-(-1,4-phenylenebis(ethene-2,1-diyl))bis(pyridin-1-ium)) in 64% yield. Heating 1 at 160 °C for 5 h gave rise to another 1D coordination polymer {[1,4-bpebH2][Zn(1,3,5-HBTC)(η,η,η,-μ3-1,3,5-HBTC)]·1.5H2O}n (2) in a quantitative yield. Compounds 1 and 2 were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Compound 1 consists of [Zn(H2O)(1,3,5-HBTC)] units which are interlinked by μ-1,3,5-HBTC2− ligands to form a 1D [Zn(H2O)(1,3,5-H2BTC)(μ-1,3,5-HBTC)]n2n– anionic chain with [1,4-bpebH2]2+ cations located in-between these chains. Compound 2 contains [Zn2(1,3,5-HBTC)2] units which are interconnected to yield a 1D ladder-type [Zn(1,3,5-HBTC)(η,η,η-μ3-1,3,5-HBTC)]n2n– with [1,4-bpebH2]2+ cations positioned in-between these chains. Upon heating, the anionic single chain structure of 1 undergoes a single-crystal-to-single-crystal topological transformation into the anionic ladder-shaped chain structure of 2 by replacing the coordinated water molecules in one chain via one μ-1,3,5-HBTC2− ligand in the other chain in 1. Both compounds exhibit excellent sorption performance towards Congo Red (CR) in water at room temperature with the maximum absorption capacity of 2020 mg g−1 (1) or 2320 mg g−1 (2). Compound 1 as a representative example can selectively absorb CR from its combination with selected cationic dyes in water.

Enantiopure versus Racemic Mixture in Reversible, Two-Step, Single-Crystal-to-Single-Crystal Transformations of Copper(II) Complexes.

The reaction of chiral sodium complexes, 1∞ [Na(S-valmetH)]⋅H2 O (1-S) and 1∞ [Na(R-valmetH)]⋅H2 O (1-R), with copper(II) acetate affords chiral one-dimensional coordination polymers with the formulas 1∞ [Cu(S-valmet)(H2 O)]⋅H2 O (2-S) and 1∞ [Cu(R-valmet)(H2 O)]⋅H2 O (2-R) (R/S-valmetH2 are Schiff base proligands resulting from the condensation reactions between o-vanillin and R/S-methionine). The copper ions are connected by the carboxylato groups belonging to the amino-acid moieties, resulting in infinite chains showing syn-anti out-of-plane bridging mode. The circular dichroism spectra of 1-S, 1-R, 2-S, and 2-R confirm their enantiomeric nature. Compounds 2-S and 2-R undergo a two-step single-crystal-to-single-crystal transformation, with the elimination of the lattice and coordinated water molecules: 1∞ [Cu(S-valmet)(H2 O)]⋅H2 O (2-S)→1∞ [Cu(S-valmet)]⋅H2 O (3-S⋅H2 O)→1∞ [Cu(S-valmet)] (3-S) and 1∞ [Cu(R-valmet)(H2 O)]⋅H2 O (2-R)→1∞ [Cu(R-valmet)]⋅H2 O (3-R⋅H2 O)→1∞ [Cu(R-valmet)] (3-R), respectively. During these transformations, every pair of face-to-face chains present in 2-S (or 2-R) has been "zipped up" into a chiral double chain through the removal of the aqua ligands and their replacement by the carboxylato oxygen atoms from the neighboring chain. Consequently, each carboxylato group now bridges three copper ions. The conversion of the single chains, 2-S and 2-R, into the double chains, 3-S and 3-R, is accompanied by a change of the strength of the exchange interactions between the copper ions: weak antiferromagnetic couplings are observed in compound 2-S (J/kB =-1.23(5) K, H=-2J ΣSi Si+1 ) and relatively strong in compound 3-S (J/kB =-76.0(8) K). When the racemic mixture of the ligands, R,S-valmetH2 , is employed, in the same experimental conditions, a racemic mixture of mononuclear compounds, [Cu(R,S-valmet)(H2 O)2 ]⋅H2 O (4-RS), is obtained. Compound 4-RS also undergoes a SCSC transformation with the elimination of the lattice and one of the coordinated water molecules, resulting in a racemic mixture of chiral chains, 1∞ [Cu(R-valmet)(H2 O)]⋅1∞ [Cu(S-valmet)(H2 O)] (5-RS). In this compound, the coupling of the copper(II) ions within the chains is weak and ferromagnetic (J/kB =+0.10(2) K). These results prove that the chirality of the valmetH2 ligands (optically pure or racemic mixture) plays a key role in the self-assembly process of the copper(II) complexes.

Cyclic OFF/Part/ON switching of single-molecule magnet behaviours via multistep single-crystal-to-single-crystal transformation between discrete Fe(ii)-Dy(iii) complexes.

Upon dehydration, a dinuclear Fe(ii)-Dy(iii) cluster {FeDy(H2O)2} undergoes two-step single-crystal-to-single-crystal (SCSC) transformation, giving another dinuclear cluster {FeDy(H2O)} and finally a tetranuclear cluster {Fe2Dy2}. Further, both the single crystals of {FeDy(H2O)} and {Fe2Dy2} can return to {FeDy(H2O)2} by rehydration. This multistep SCSC transformation leads to notable OFF/Part/ON switching of single-molecule magnet behaviour.