Single-crystal Transformation Research Articles

Effect of pre-intercalation on Li-ion diffusion mapped by topochemical single-crystal transformation and operando investigation.

Limitations in electrochemical performance as well as supply chain challenges have rendered positive electrode materials a critical bottleneck for Li-ion batteries. State-of-the-art Li-ion batteries fall short of accessing theoretical capacities. As such, there is intense interest in the design of strategies that enable the more effective utilization of active intercalation materials. Pre-intercalation with alkali-metal ions has attracted interest as a means of accessing higher reversible capacity and improved rate performance. However, the structural basis for improvements in electrochemical performance remains mostly unexplored. Here we use topochemical single-crystal-to-single-crystal transformations in a tunnel-structured ζ-V2O5 positive electrode to illustrate the effect of pre-intercalation in modifying the host lattice and altering diffusion pathways. Furthermore, operando synchrotron X-ray diffraction is used to map Li-ion site preferences and occupancies as a function of the depth of discharge in pre-intercalated materials. Na- and K-ion intercalation 'props open' the one-dimensional tunnel, reduces electrostatic repulsions between inserted Li ions and entirely modifies diffusion pathways, enabling orders of magnitude higher Li-ion diffusivities and accessing higher capacities. Deciphering the atomistic origins of improved performance in pre-intercalated materials on the basis of single-crystal-to-single-crystal topochemical transformation and operando diffraction studies paves the way to site-selective modification approaches for positive electrode design.

The effect of heat treatment on microstructure and martensitic transformation temperatures in Ni44Fe19Ga27Co10 single crystals

Abstract The microstructure and temperature of martensitic transformation of Ni44Fe19Ga27Co10 single crystals after aging at temperatures from 623 K to 1173 K were studied by electron microscopy and differential scanning calorimetry. The temperature ranges of the second phase precipitation, their lattice structure and volume fraction, and also the modification of the nanodomain structure of the L21+B2 high-temperature phase were determined in dependence on aging temperature. The influence of microstructure parameters on the martensitic transformation temperatures, transformation intervals and thermal hysteresis has been discussed.

The effect of Sc doping on the electrocatalytic and optoelectronic properties of 2D SiAs single crystals

The p–n transformation of SiAs single crystals is realized by Sc doping, and their photoelectric detection and catalytic properties are effectively improved.

Designing multifunctional organic thermochromic ferroelectric materials: remarkable melt-cool large thermal hysteresis of reversible single crystal to single crystal transformation

A comprehensive study of chiral N-benzylideneaniline analogues for their structural and material properties.

A donor–acceptor hydrogen-bonded organic framework with the turn-on fluorescence response of phenethylamine (drug analogue) via single-crystal to single-crystal transformation

A water-stable hydrogen-bonded organic framework (TPPA-TMA) material has been constructed which can act as the first example of a HOF-implicated turn-on sensor for phenylethylamine via single-crystal to single-crystal transformation.

Temperature induced single-crystal to single-crystal transformation of uranium azide complexes.

The monomeric and dimeric uranium azide complexes {[(CH3)2NCH2CH2NPiPr2]2U(N3)2} (2) and {[(CH3)2NCH2CH2NPiPr2]2U(N3)2}2 (3) were synthesized by treating complex 1 with NaN3 at 60 and -20 °C, respectively. A temperature-induced single-crystal to single-crystal transformation of 3 to 2 was observed. The reduction of either 2 or 3 with KC8 yields a uranium nitride complex {[(CH3)2NCH2CH2NPiPr2]4U2(μ-N)2} (4).

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.

Synergistic Induction of Solvent and Ligand-Substitution in Single-Crystal to Single-Crystal Transformations toward a MOF with Photocatalytic Dye Degradation.

External-stimuli responsiveness as found in natural organisms and smart materials is attractive for functional materials scientists who attempt to design and imitate fascinating behavior into their materials. Herein, we report a couple of new solvent-responsive isostructural two-dimensional cationic metal-organic frameworks (MOFs) of Mn(II) (1a) and Zn(II) (2a) that undergo unprecedented single-crystal to single-crystal (SCSC) transformation toward the corresponding isostructural three-dimensional MOFs of Mn(II) (1b) and Zn(II) (2b). The 2D MOFs 1a and 2a have been effortlessly and rapidly synthesized via the microwave-heating technique. The SCSC transformations are synergistically induced by solvent and ligand-substitution reactions and able to be triggered by water, methanol, ethanol, and n-propanol. Time-dependent SCSC transformations were studied by in situ X-ray diffraction. Investigations on photodegradation of methyl orange showed that Zn-MOF 2b has higher efficiency than Mn-MOF 1b under UV-C irradiation at 300 min, 94.27%, and 21.91%, respectively. The influence of charge on the dye molecules, heterogeneity of the catalysis, and •OH radical-scavenging test was studied. First-principles computations suggest that the high photocatalytic activity of 2b may be attributed to its suitable band-edge position for redox reactions.

Single-Crystal Transformation Engineering the Spin Change of Metal-Organic Frameworks via Cluster Deconstruction.

Spin crossover (SCO) materials with new architectures will expand and enrich the research in the SCO field. Here, we report two metal-organic frameworks (MOFs) containing tetradentate organic ligands and hexatopic linkers [Ag8X8(CN)6]6- (X = Br and I), which represents the first SCO MOF with clusters as building blocks. The silver halide cluster can be further removed after reacting with LiTCNQ. Such post-synthetic modification (PSM) is realized via single-crystal to single-crystal (SCSC) transformation from urk to nbo topology. Accordingly, the spin state and fluorescence properties are greatly modified by cluster deconstruction. These achievements will provide new ideas for the design of new SCO systems and the development of PSM methods.

Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks.

Porous sorbents are materialsutilizedfor various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, herein, we report a rare example of "crossover sorption," in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized twosoft porous coordination polymers, [Zn2(L1)(L2/L3)2]n(PCP-1/2) (L1 = 4,4'-bis(4-pyridyl)phenyl; L2 = 5-methyl-1,3-di(4-carboxyphenyl)benzene; L3 = 5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPsexhibits structural changes upon gas sorption and show the crossover sorption for both C2H2/CO2and C2H6/C2H4, where the apparent affinity reverse with temperature. We used in-situ gas-loading single-crystal X-ray diffraction (SCXRD) analyses to reveal the guest-inclusion structures of PCP-1 at various temperatures.Interestingly, we observed three-step single-crystal-to-single-crystal transformations with the different loading phases under these gases, providing insight into guest-binding positions, nature of host-guest or guest-guest interactions. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host-guest and guest-guest interactions.

Crystal Sponge Behavior in a Two-Dimensional Rare-Earth Hybrid Coordinate Polymer.

Stimuli-responsive multifunctional materials (SRMMs) have attracted tremendous attention due to their dynamic responses to external stimuli. However, it remains challenging to simultaneously achieve solvent-induced single-crystal to single-crystal (SCSC) transformation and structural phase transition after desolvation. Here, we report a two-dimensional (2D) rare-earth organic-inorganic hybrid coordinate polymer [(CH3)3NCH2Cl]2[Eu·H2O]2[CH2(SO3)2]4·2H2O (1) that exhibits a reversible SCSC transformation by changing to 2 ([(CH3)3NCH2Cl][Eu·H2O][CH2(SO3)2]2). Impressively, the SCSC transformation process couples with large changes in quantum efficiency dropped from 33.68% of 1 to 20.07% that of 2. Furthermore, polymer 2 shows an isomorphic structural phase transition associated with switching dielectric. Notably, the distance of the 2D layers shows reversible change during the two successive transition processes displaying a crystal sponge behavior. This work reveals the potential of rare-earth 2D hybrid coordination polymers in the design of multifunctional responsive materials and opens a new prospect to explore the construction of novel SRMMs.

Single-Crystal to Single-Crystal Transformation of a 0D Cu(II) Metallocycle into a 1D Coordination Polymer Triggered by Spontaneous Desolvation in Mother Liquor

Single-Crystal to Single-Crystal Transformation of a 0D Cu(II) Metallocycle into a 1D Coordination Polymer Triggered by Spontaneous Desolvation in Mother Liquor

Multidirectional Solvent-Induced Structural Transformation in Designing a Series of Polycatenated Cobalt(II) Coordination Polymers: Impact on Carbon Dioxide and Hydrogen Uptake.

Coordination polymers with external stimuli-responsive structural transformation acquired paramount importance in the advanced material research field due to their eye-catching application to deal with the existing challenging issue, and Co(II) metal complex with d7 electronic configuration is a renowned candidate for kinetic accountability and has the potentiality of structural transformation. Bearing these factors in mind, here, a Co(II) congener of a previously reported high hydrogen-adsorbing Cu(II)-based coordination polymer (CP), {[Cu(4-bpe)(2-ntp)]}n [where 2-ntp2- = 2-nitroterephthalate and 4-bpe = 1,2-bis-(4-pyridyl)ethane], has been synthesized to study the metal change impact on hydrogen adsorption and solvent-induced structural transformation with their impact on hydrogen uptake. This modified framework has a 2D + 2D → 3D inclined polycatenated framework as comparable to our previously published Cu(II) framework. Here, on the variation of different solvents, the labile Co(II)-containing framework exhibits a structural change through single-crystal to single-crystal (SC-SC) structural transformation and results in three new framework structures. All four frameworks are structurally characterized by elemental analysis, IR, PXRD, TGA, and single-crystal X-ray diffraction. The desolvated parent framework with exposed metal centers exhibits excellent results of H2 adsorption of 1.3 wt % (145 cc/g) at 77 K and pressure of 1 bar with structural sustainability and CO2 uptake of 130 cc/g at 195 K and 1 bar. For the other three solvent-mediated structural derivatives, H2 and CO2 adsorption have been studied, and the results are correlated with their structure.

The mechanism of hcp-bcc phase transformation in Mg single crystal under high pressure

The mechanism of phase transformation from hexagonal close-packed (hcp) to body-centered-cubic (bcc) structure in Mg single crystal under high pressure is studied by molecular dynamics (MD) simulations. The hcp-bcc phase transformation is achieved by a shear-shuffle mechanism, through the formation of bcc nanotwinned structure and the subsequent detwinning. The nanotwinned structure can effectively accommodate the shear caused by the hcp-bcc phase transformation, which facilities the growth of bcc phase under hydrostatic pressure. The detwinning turns the bcc nanotwinned structure into bcc nano-polycrystalline. Two twinning modes with the opposite twinning shear occur during the detwinning, which can accommodate the shear in different directions. The mechanism of hcp-bcc phase transformation revealed in this work brings out a comprehensive understanding of the plastic mechanism under high pressure, which is helpful for the further materials design under high pressure.

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.

Photoresponsive Magnetic Relaxation Behavior of a Highly Stable π···π Interaction-Stacked Framework Based on a DyIII Single-Ion Magnet

Endowing lanthanide single-ion magnets (Ln-SIMs) with high stability and stimulus responsiveness is of significance for the practical applications of these novel magnetic materials, but still of challenge at present. Herein, we report on a highly stable and photoresponsive Ln-SIM system achieved by designing and synthesizing a π···π interaction-stacked framework based on DyIII-SIM (πOF-1). Its molecular formula is [Dy(thqa)] (H3thqa = tris[(8-hydroxyquinoline-2-yl)methylene]amino). Each of its C3-symmetric molecules consists of a thqa3– ligand and a DyIII ion, and it is linked to three neighbors by intermolecular π···π interactions, forming a supermolecular two-dimensional (2D) honeycombed topology. Such unique structure endows πOF-1 with not only air and thermal stability but also excellent chemical stability in different solvents, even in alkali solutions, including a 20 M NaOH aqueous solution. Dual magnetic relaxation behavior was observed in πOF-1. Magnetic dilution revealed that it is related to π···π-mediated intermolecular magnetic interactions. More significantly, both the static magnetic susceptibility and the dual-relaxation behavior of πOF-1 show response to photoirradiation, which could be ascribed to the photo-triggered intermolecular π → π* charge transfer (CT). So far as we know, πOF-1 could be the first Ln-SIM system possessing both a high stability and photoresponsiveness, and also the first photoresponsive Ln-SIM supermolecular system that does not rely on the single-crystal to single-crystal (SCSC) structural transformation. Its successful design and synthesis suggests that the introduction of π···π interactions can be a new strategy to fabricate stable and/or photoresponsive Ln-SIMs.

Surface Effect on Phase Transformation of Single Crystal NiTi Shape Memory Alloys Studied by Molecular Dynamics Simulation

Surface effect on phase transformation of single crystal (SC) NiTi shape memory alloys (SMAs) with various thicknesses and various Ni contents is studied by molecular dynamics simulation. For the SMAs with various thicknesses considering surface effect, the residual strain, the average atomic potential energy, and the four characteristic phase transformation temperatures all increase, and fewer twinned martensite boundaries are left after cooling compared to the sample without considering surface effect. Moreover, with increasing thickness of the sample, the surface effect is gradually weakened, and there is no obvious regularity in phase transformation characteristics. For the SMAs with various Ni contents considering surface effect, segmental martensite phase transformation, phase transformation fluctuation, and wider phase transformation temperature ranges are observed, whereas these phenomena do not occur in the sample without considering surface effect. With the increasing of Ni contents, for both cases of considering surface effect or not, the critical stress of phase transformation, average atomic potential energy, the modulus of detwinned martensite increase, but the phase transformation temperature and modulus of twinned martensite decrease.

Structural transformation and magnetic properties of Co(II) coordination polymers with pyrazole-3,5-dicarboxylate and pyrazine

A two-dimensional (2D) Co(II) coordination polymer with rectangular channel, namely {[Co2(Hpzdc)2(pyz)(CH3OH)(H2O)2]⋅3H2O}n (1) was synthesized under the solvothermal condition (Hpzdc = pyrazole-3,5-dicarboxylate and pyz = pyrazine). Both Co(II) centers exhibit octahedral geometry. The coordinated methanol and all water molecules in 1 can be removed by heating to give rise to the amorphous phase of desolvated 1 (1a). After 1a was immersed in the mixture of water and methanol, a new isostructural {[Co2(Hpzdc)2(pyz)(H2O)3]⋅3H2O}n (2) was obtained. The replacement of water for methanol in 1 leads to an alteration in the intermolecular packing, which gives rise to the color variations. The single-crystal to amorphous to single-crystal transformations accompanied by the color changes were confirmed by single crystal X-ray structure analysis, XRPD, TGA, elemental analysis, and spectroscopic techniques. The magnetic properties of 1 and 2 exhibit the antiferromagnetic interaction and spin–orbit coupling of octahedral high-spin Co(II) ion.

Single-Crystal to Single-Crystal Transformations: Stepwise CO2 Insertions into Bridging Hydrides of [(NHC)CuH]2 Complexes.

Mechanistic studies of substrate insertion into dimeric [(NHC)CuH]2 (NHC=N-heterocyclic carbene) complexes with two bridging hydrides have been shown to require dimer dissociation to generate transient, highly reactive (NHC)Cu-H monomers in solution. Using single-crystal to single-crystal (SC-SC) transformations, we discovered a new pathway of stepwise insertion of CO2 into [(NHC)CuH]2 without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH]2 (IPr*OMe=N,N'-bis(2,6-bis(diphenylmethyl)-4-methoxy-phenyl)imidazole-2-ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu]2 (μ-1,3-O2 CH)(μ-H). A second CO2 insertion produced a dicopper bis(formate), [(IPr*OMe)Cu]2 (μ-1,3-O2 CH)(μ-1,1-O2 CH), containing two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core cleanly ruptures to monomeric complexes when dissolved in a solvent.

Detection of electromagnetic phase transitions using a helical cavity susceptometer.

Fast and sensitive phase transition detection is one of the most important requirements for new material synthesis and characterization. For solid-state samples, microwave absorption techniques can be employed for detecting phase transitions because it simultaneously monitors changes in electronic and magnetic properties. However, microwave absorption techniques require expensive high-frequency microwave equipment and bulky hollow cavities. Due to size limitations in conventional instruments, it is challenging to implement these cavities inside a laboratory cryostat. In this work, we designed and built a susceptometer that consists of a small helical cavity embedded into a custom insert of a commercial cryostat. This cavity resonator operated at sub-GHz frequencies is extremely sensitive to changes in material parameters, such as electrical conductivity, magnetization, and electric and magnetic susceptibilities. To demonstrate its operation, we detected superconducting phase transition in Nb and YBa2Cu3O7-δ, metal-insulator transitions in V2O3, ferromagnetic transition in Gd, and magnetic field induced transformation in meta magnetic NiCoMnIn single crystals. This high sensitivity apparatus allows the detection of trace amounts of materials (10-9-cc) undergoing an electromagnetic transition in a very broad temperature (2-400K) and magnetic field (up to 90 kOe) ranges.