SCSC Transformation Research Articles

Solvent-induced SC-SC transformation between 3D and 1D Co-MOFs: Fluorescence sensing and magnetic properties

Solvent-induced SC-SC transformation between 3D and 1D Co-MOFs: Fluorescence sensing and magnetic properties

Guest-Induced Reversible Single-Crystal-to-Single-Crystal Transformation Involving Displacement of 2D Layers and Spin Crossover Behavior Change in a Hofmann-Type Coordination Polymer.

A novel two-dimensional (2D) Hofmann-type coordination polymer, {FeII(PyHbim)2[Pd(CN)4]}·2CH3OH [1·2CH3OH, PyHbim = 2-(4-pyridyl)benzimidazole], has been synthesized, which can undergo a spontaneous guest exchange, transforming to 1·2H2O in a single-crystal-to-single-crystal (SCSC) manner, shifting from orthorhombic Cmmm to monoclinic C2/m involving the displacement of 2D layers. The solvent-induced SCSC transformation process was reversible and verified through powder X-ray diffraction (PXRD) and single-crystal X-ray crystallography analyses. Both 1·2CH3OH and 1·2H2O exhibit complete and abrupt spin crossover (SCO) behaviors in two steps, while their SCO temperature ranges drastically shift by ca.100 K, spanning room temperature, owing to different intermolecular interactions resulting from diverse interlayer packing manners and host-guest interactions. Besides, a structural phase transition is observed in 1·2CH3OH, contributing to the two-step spin transition.

Regulating photoluminescence through single-crystal-to-single-crystal transformation of solvent-containing zero-dimensional hybrid metal halide isomers

Regulating photoluminescence (PL) properties induced by single-crystal-to-single-crystal (SCSC) transformation has sparked significant interest in the research of zero-dimensional organic–inorganic metal halides (0-D OIMHs). To best of our knowledge, the SCSC transformation of solvent-containing 0-D OIMH isomers hasn’t been reported yet. In this work, we report the first example of SCSC transformation between two isomers containing lattice solvent molecules, namely α- and β-[EtPPh3]2[SbCl5]·MeCN (α- and β-1·MeCN; EtPPh3 = ethyltriphenylphosphonium; MeCN = acetonitrile). Differential scanning calorimetry (DSC) results show that the SCSC transformation from α- to β-1·MeCN is an exothermic process, implying that β-1·MeCN is a more stable phase than α-1·MeCN. Moreover, α- and β-1·MeCN exhibit bright orange (emission peak: 610 nm) and red (emission peak: 635 nm) emission under 360/365 nm excitation, respectively. DFT calculations suggest that the negligible self-absorption and a strong exciton confinement contribute to their effective PL emission. By analyzing temperature-dependent PL spectra, β-1·MeCN has been found to exhibit stronger electron-phonon coupling under excitation than α-1·MeCN. Thus, the broader emission with full width at half maximum (FWHM: 134 vs. 147 nm) and the higher photoluminescence quantum yield (PLQY: 40.37% vs. 70.50%) have been realized by SCSC transformation from α- to β-1·MeCN by heating at 92 °C. Benefitting from the regulation of PL performances brought by SCSC transformation, the white light-emitting-diode (LED) devices assembled by using β-1·MeCN as red phosphor could be optimized, and the CRI reaches as high as 95.3.

A cobalt(II) coordination polymer-derived catalyst engineered via temperature-induced semi-reversible single-crystal-to-single-crystal (SCSC) dehydration for efficient liquid-phase epoxidation of olefins.

Single-crystal-to-single-crystal (SCSC) transformations provide more avenues for phase transitions, which have piqued great interest in crystal engineering. In this work, a 3D Co(II)-based coordination polymer (CP), {Co2(OH2)8(btec)}·4H2O (1), (where (btec)4- = 1,2,4,5-benzenetetracarboxylate) undergoes SCSC transition upon heating at 180 °C to afford an anhydrous phase [Co2(btec)] (1'). Room-temperature water-vapour induced semi-reversible SCSC transformation of 1' involves condensation of two water molecules coordinating to the metal cluster, yielding a new framework [Co2(OH2)2(btec)] (2). These SCSC transitions were accomplished through a sequential bond breaking and new bond formation process which was accompanied by colour changes from orange (1) → violet (1') → pink (2). All materials were structurally elucidated by single-crystal X-ray diffraction (SCXRD) and further established by various analytical techniques. According to SCXRD data, all the frameworks possess octahedral geometries around the cobalt(II) sphere. SCXRD studies further revealed that 1 is a polymeric architecture with a binodal 4-c sql topology while 1' and 2 possess (3,6)-c kgd and (4,6)-c scu 3D nets, respectively. By virtue of multitopicity exhibited by the tetracarboxylate, the coordination number of the linker around the Co(II) sphere increased from four (in 1) to eight (in 1') and then decreased to six (in 2). Most interestingly, permanent porosity could be observed for the dihydrate 2, originated from potential void space as substantiated by dinitrogen (N2) sorption isotherm. These porous frameworks were active catalysts for the aerobic epoxidation of the model substrate cyclohexene using molecular oxygen (O2) as the final oxidant in the presence of the sacrificial i-butyraldehyde (IBA) reductant. For using the dihydrous phase 2, cyclohexene and various other olefins were catalytically oxidised to their corresponding epoxides with up to 38.5% conversion and 99.0% selectivity. The catalyst 2 can be expediently recycled in four runs without significant loss of activity. This research demonstrates that a little innovation in the active-site-engineered organic-inorganic hybrid materials can significantly enhance the catalytic performance and selectivity of coordination polymer-derived heterogeneous catalysts.

Solvent- and tatrz-induced single-crystal-to-single-crystal transformations within cobalt(ii)-triazole MOFs: a luminescent probe for frankincense

MOF 1 with tatrz and ipa was isolated. Solvent-exchange experiment indicated that water molecules can be replaced by DMF during the SC-SC transformation process. When immersed MOF 1 in tatrz solution, MOF 3 can be obtained.

The AM-4 Family of Layered Titanosilicates: Single-Crystal-to-Single-Crystal Transformation, Synthesis and Ionic Conductivity.

Flexible crystal() structures, which exhibit() single-crystal()-to-single-crystal() (SCSC) transformations(), are attracting attention() in many applied aspects: magnetic() switches, catalysis, ferroelectrics and sorption. Acid treatment() for titanosilicate material() AM-4 and natural() compounds with the same structures led to SCSC transformation() by loss() Na+, Li+ and Zn2+ cations with large structural() changes (20% of the unit()-cell() volume()). The conservation() of crystallinity through complex() transformation() is possible due() to the formation() of a strong hydrogen bonding() system(). The mechanism() of transformation() has been characterized using single-crystal() X-ray() diffraction analysis(), powder() diffraction, Rietvield refinement, Raman spectroscopy and electron microscopy. The low migration() energy() of cations in the considered materials() is confirmed using bond()-valence and density() functional() theory() calculations, and the ion conductivity of the AM-4 family's materials() has been experimentally verified.

Direct observation on single-crystal-to-single-crystal transformation via lattice-matched nucleation and growth

Single-crystal-to-single-crystal (SCSC) phase transformation has been showing its great significances for controllable synthesis of advanced materials. From this point of view, the atomic-scale understanding of structural dynamics during SCSC transformation is of fundamental criticality for its utilizations in many disciplines, which, however, remains a grand challenge due to the lack of direct and effective experimental probes. Here, we report a complete observation regarding atomic-scale mechanisms for nucleation and growth of a hexagonal phase in a monoclinic matrix during a heating-induced structural transformation using in situ transmission electron microscopy. The overall process consists of several distinct steps; namely, defect generation, phase nucleation, phase growth and propagation. In particular, the new hexagonal phase is found to nucleate at defect-rich high-energy surface regions of the matrix, and subsequently grow in a lattice-matched manner between the old monoclinic and new hexagonal phases, thus maintaining the single-crystalline nature of the product phase during the whole transformation, even in the case of discrete nucleation at multiple sites. Such findings provide crucial insights for the understanding of microscopic mechanisms and kinetics of solid-state phase transitions.

Structural and Theoretical Study of Copper(II)-5-fluoro Uracil Acetate Coordination Compounds: Single-Crystal to Single-Crystal Transformation as Possible Humidity Sensor.

This paper describes the synthesis and characterization of seven different copper(II) coordination compounds, as well as the formation of a protonated ligand involving all compounds from the same reaction. Their synthesis required hydrothermal conditions, causing the partial in situ transformation of 5-fluoro uracil-1-acetic acid (5-FUA) into an oxalate ion (ox), as well as the protonation of the 4,4'-bipyridine (bipy) ligand through a catalytic process resulting from the presence of Cu(II) within the reaction. These initial conditions allowed obtaining the new coordination compounds [Cu2(5-FUA)2(ox)(bipy)]n·2n H2O (CP2), [Cu(5-FUA)2(H2O)(bipy)]n·2n H2O (CP3), as well as the ionic pair [(H2bipy)+2 2NO3-] (1). The mother liquor evolved rapidly at room temperature and atmospheric pressure, due to the change in concentration of the initial reagents and the presence of the new chemical species generated in the reaction process, yielding CPs [Cu(5-FUA)2(bipy)]n·3.5n H2O, [Cu3(ox)3(bipy)4]n and [Cu(ox)(bipy)]n. The molecular compound [Cu(5-FUA)2(H2O)4]·4H2O (more thermodynamically stable) ended up in the mother liquor after filtration at longer reaction times at 25 °C and 1 atm., cohabiting in the medium with the other crystalline solids in different proportions. In addition, the evaporation of H2O caused the single-crystal to single-crystal transformation (SCSC) of [Cu(5-FUA)2(H2O)(bipy)]n·2n H2O (CP3) into [Cu(5-FUA)2(bipy)]n·2n H2O (CP4). A theoretical study was performed to analyze the thermodynamic stability of the phases. The observed SCSC transformation also involved a perceptible color change, highlighting this compound as a possible water sensor.

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Visible Light‐fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals

AbstractIn the quest for essential energy solutions towards an ecological friendly future, the transformation of visible light/solar energy into mechanical motions in metal‐free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, and all‐organic electronic devices. Such green energy‐triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid‐base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both ultraviolet (UV) and visible light associated with quantitative single‐crystal‐to‐single‐crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light‐promoted dynamic green RTP as their emission peaks promptly blue‐shift, due to instantaneous photomechanical effects. Time‐dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X‐ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light‐driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli‐responsive multi‐functional crystalline materials.

Visible Light-fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals.

In the quest for essential energy solutions towards an ecological friendly future, the efficient transformation of visible light/solar energy into mechanical motions in metal-free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, sensing, and all-organic electronic devices. Such green energy-triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid-base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both UV and visible light associated with quantitative single-crystal-to-single-crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light-promoted dynamic green RTP as their emission peaks promptly blue-shift, due to instantaneous photomechanical effects. Time-dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X-ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light-driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli-responsive multi-functional crystalline materials.

SCSC Transformation and Post-Synthesis Modification of MOFs with Proton Conduction and Ratiometric Fluorescence-Sensing Properties.

The modification of metal-organic framework (MOF) materials to facilitate their practical applications is an extremely challenging and meaningful topic. In this work, two stepwise modification strategies for MOFs were conducted. First, we have demonstrated a single-crystal-to-single-crystal (SCSC) transformation from a microporous three-dimensional (3D) MOF to a two-dimensional (2D) coordination polymer (CP). The centrosymmetric [Cd(3-bpdb)(MeO-ip)]n (1) transforms into a chiral [Cd2(3-bpdb)(MeO-ip)2(CH3OH)2]n (2), which is triggered by the reaction time with methanol that acts as a structure-directing agent. The conversion relationship of 1 to 2 at different reaction times was studied in detail. Density functional theory (DFT) calculations clearly state that the irreversible formation of 2 is thermodynamically favorable. Intriguingly, 2 exhibits good proton conduction of 1.34 × 10-3 S cm-1 under 363 K and 98% relative humidity (RH) due to unique H-bond network characteristics. To the best of our knowledge, there are very few cases of 3D to 2D SCSC transformation stimulated by reaction time. The results have important implications for understanding the SCSC transformation mechanism and synthetic chemistry. On the other hand, the lanthanide3+-functionalized hybrids (Ln3+-MOF), Ln3+@1, were continuously prepared by incorporating luminescent Ln3+ ions into the structure of 1 through encapsulating post-synthesis modification (PSM). Tb3+@1 exhibits double emission in water and shows visual ratiometric fluorescence behavior for sensing glutamic acid (Glu), tryptophan (Trp), and Al3+, which is more reliable and accurate than single emission. Our work may not only provide new insights into the multiple modification of MOF materials but also promote the practical application of such materials.

ON/OFF Photo(switching) along with Reversible Spin-State Change and Single-Crystal-to-Single-Crystal Transformation in a Mixed-Valence Fe(II)Fe(III) Molecular System.

A mixed-valence Fe(II)Fe(III) molecular system, {[Fe(pzTp)(CN)3]2[Fe(bik)2]2}·[Fe(pzTp)(CN)3]2·4MeOH (1·4MeOH) (bik = bis-(1-methylimidazolyl)-2-methanone, pzTp = tetrakis(pyrazolyl)borate), exhibits single-crystal-to-single-crystal (SC-SC) transformation while increasing the temperature and is converted into {[Fe(pzTp)(CN)3]2[Fe(bik)2]2}·[Fe(pzTp)(CN)3]2 (1). Both complexes exhibit thermo-induced spin-state switching behavior along with reversible SC-SC transformation, where the low-temperature [FeIIILSFeIILS]2 phase transforms into a high-temperature [FeIIILSFeIIHS]2 phase. 1·4MeOH exhibits an abrupt spin-state switching with T1/2 at 355 K, whereas 1 undergoes a gradual and reversible spin-state switching with a lower T1/2 at 338 K. Astonishingly, 1 exhibits ON/OFF photo-induced spin-state switching with TLIESST = 67 K, whereas 1·4MeOH does not show such an effect.

Solvent-oriented structural diversity, sequential SCSC and low-temperature transformation in Cd-coordination polymers: unique turn-on–off sensing of Fe3+

Cd-1′, Cd-2, Cd-3, and Cd-4 have been synthesized in DMF–H2O systems. SCSC transformation products Cd-5, Cd-6, and Cd-7 were obtained through solvent-induced strategy and reversible phase transitions were observed, as was a turn-on–off Fe3+ ion fluorescence sensor.

Guest-induced proton conductivity of two-dimensional layered hydrogen-bonded organic frameworks

We report the self-adaptability of 2D hydrophilic channels of HOFs to guest molecules based on the cyclic SCSC transformation. The studies indicate that the proton conductivity of HOFs depends on the guest-induced hydrogen bonding networks.

Water-driven Successive Structural Transformation in a Two-Dimensional (2D) Lead-Free Hybrid Double Perovskite.

Hybrid organic-inorganic halide perovskites (HOIPs) have received continued interest for their structure diversity and potential application in optoelectronic, solar cells, nonlinear optics (NLO), and ferroelectrics. Structural symmetry breaking induced by water molecules in single-crystal-to-single-crystal (SCSC) transformations is beneficial to develop ferroelectrics or second-harmonic generation (SHG) materials. Along this line, a water-containing two-dimensional (2D) double perovskite, (C6H16N2)2AgBiBr8·H2O (1), was prepared. Acentric 1 suffered a twice SCSC transformation when subjected to dehydration and rehydration, where the new centric (C6H16N2)2AgBiBr8 (2) and acentric (C6H16N2)2AgBiBr8·0.5H2O (3) were generated. In contrast to the irreversible transformation from 1 to 2 (symmetry: P21 → Pmna), it is prominent that the reversible conversion of centric 2 to acentric 3 (symmetry: Pmna ↔ P21212). The result validated the effect of guest water on inducing structural transformation and symmetry breaking of 2D perovskites, inspiring further explorations on water-involved 2D materials.

Manipulation of the cyanido-bridged Fe2W2 rhombus in the crystalline state: Co-crystallization, desolvation and thermal treatment

We present the new cyanido-bridged rhombus {[FeII(TPMA)]2[WV(CN)8]2}2– (Fe2W2) (TPMA = tris(2-pyridylmethyl)amine) cluster as a potential Secondary Building Block (SBB) for construction of polynuclear molecular materials. Fe2W2 is formed easily in self-assembly process between [FeII(TPMA)]Cl2 and TBA3[W(CN)8] in H2O/MeOH media, and was co-crystallized in (TBA)2{Fe2W2}⋅2H2O (1), and (TBA)2{Fe2W2}⋅mMeOH⋅nH2O (2) solvated salts, and in (TBA)2{Fe2W2}⋅H3PG⋅mMeOH⋅nH2O (3) (H3PG = phloroglucinol, 1,3,5-trihydroxybenzene; co-former) solvated co-crystal salt. Crystals of 1 undergo reversible SCSC transformation 1 ⇄ 1deh upon controlled dehydration and rehydration processes, whereas crystals of 2 reveal anisotropic thermal expansion during heating from 100 K to room temperature. Both processes involve changes of the selected intermolecular distances or local molecular reorientation involving intermolecular cation–anion and anion-anion contacts. [FeII(TPMA)(µ-NC)2] moieties reveal low-spin (LS) state in each case, however, conformation of the Fe2W2 rings varies from the “staggered” in 1, nearly “eclipsed” in 2 to fully “eclipsed” in 3, which is attributed to various hydrogen bond CNN⋅⋅⋅HO schemes involving the terminal cyanido ligands in [W(CN)8]3– and co-crystallizing molecules. In particular, the conformation of Fe2W2 in 3 is fully controlled by an unprecedented cyclic double hydrogen bond {Fe2W2}⋅⋅⋅H3PG synthon, H3PG forming a bridge over the Fe2W2 rhombus plane through binding the opposite [W(CN)8] corners. This arrangement is co-stabilized by close-to-parallel contacts of H3PG with TPMA walls protruding out of the rhombus plane. The Fe2W2 rhombus is stable in MeOH solution and shows notable affinity to H3PG in the gas phase, which was confirmed by ESI-MS data. UV–Vis-NIR spectroscopy discloses an optical FeII → WV MMCT transition and mixed-valence FeII//III-WV/IV electronic ground state.

Reversible and Stepwise Single-Crystal-to-Single-Crystal Transformation of a Platinum(II) Complex with Vapochromic Luminescence.

The vapochromic single-crystal-to-single-crystal (SCSC) transformation of a highly luminescent PtII complex bearing an N-heterocyclic carbene [Pt(CN)2 (tBu-impy)] (tBu-impyH+ =1-tert-butyl-3-(2-pyridyl)-1H-imidazolium) is reported. The trihydrate form of the complex, which exhibits blue 3 MMLCT emission owing to weak Pt⋅⋅⋅Pt interactions, changed its luminescence color from blue to yellowish-green upon the desorption of water molecules while keeping the high emission quantum yield of more than 0.45. Variable-temperature and continuous in-situ tracking of single-crystal X-ray diffraction measurements revealed that the SCSC transformation proceeds reversibly by the release and reabsorption of water molecules, thereby changing the stacked structure slightly. As a result, the dynamics of vapor-induced SCSC transformation were elucidated: that the anhydrous form returned to the original trihydrate form in a two-step process under a water vapor atmosphere. In addition, the PtII complex exhibited a similar SCSC response accompanied by a luminescence color change in the presence of methanol vapor, while being inactive toward ethanol vapor.

Single-Crystal-to-Single-Crystal Transformation of Two Copper(II) Metal-Organic Frameworks Modulated by Auxiliary Ligands.

The single-crystal-to-single-crystal (SCSC) transformations of metal-organic frameworks (MOFs) are fascinating because we can directly observe the change of the crystal structure during the transformation process. It also greatly helps to understand the delicate interaction between the guest molecules and the skeleton framework and therefore fosters a deep understanding of gas storage and separation within the frameworks. Herein, we report two novel MOFs, [Cu8(BCB)4(μ3-OH)2(μ3-O)(H2O)8(Py)5]·16DMF·52H2O (1) and [Cu3(BCB)2(Py)6]·DMF·11H2O (2) (Py = pyridine; DMF = N,N'-dimethylformamide), which were constructed through the self-assembly of Cu2+ and 4,4',4″-benzenetricarbonyltribenzoic acid (H3BCB) by a solvothermal reaction. Although the structure and coordination patterns of compound 1 are pretty different from those of 2, the two Cu-MOFs were prepared from identical ligands and similar reaction conditions. Interestingly, compound 1 will change to 2 wholly and gradually after the addition of a certain amount of Py with a small amount of dilute hydrochloric acid. This conversion represents a scarce example of SCSC transformation involving transition-metal-based MOFs. Moreover, with its microporous nature, compound 2 shows large carbon dioxide (CO2) uptake capability and good selectivity for CO2/N2 separation. Furthermore, both compounds 1 and 2 could be used as excellent heterogeneous catalysts toward the cyanosilylation reaction under solvent-free conditions.

Temperature- and solvent-induced reversible single-crystal-to-single-crystal transformations of TbIII-based MOFs with excellent stabilities and fluorescence sensing properties toward drug molecules

The water and pH stabilities of JXUST-12 have been greatly improved by SCSC transformation and JXUST-12a exhibits high selectivity and sensitivity toward drug.