Single-crystal Transformation Research Articles

Air-Stable Radical Organic Cages as Cascade Nanozymes for Enhanced Catalysis.

The pursuit of single-assembled molecular cage reactors for complex tandem reactions is a long-standing target in biomimetic catalysis but still a grand challenge. Herein, nanozyme-like organic cages are reported by engineering air-stable radicals into the skeleton upon photoinduced electron transfer. The generation of radicals is accompanied by single-crystal structural transformation and exhibits superior stability over six months in air. Impressively, the radicals throughout the cage skeleton can mimic the peroxidase of natural enzymes to decompose H2 O2 into OH· and facilitate oxidation reactions. Furthermore, an integrated catalyst by encapsulating Au clusters (glucose oxidase mimics) into the cage has been developed, in which the dual active sites (Au cluster and radical) are spatially isolated and can work as cascade nanozymes to prominently promote the enzyme-like tandem reaction via a substrate channeling effect.

The Effect of Thermal Treatment on Microstructure and Thermal-Induced Martensitic Transformations in Ni44Fe19Ga27Co10 Single Crystals

Heat treatments of single crystals of Ni44Fe19Ga27Co10 (at.%) shape memory alloys cause various microstructures of the high-temperature phase. The nanodomain structure, consisting of regions of the L21- and B2-phases, and nanosized particles are the main parameters that change during heat treatments and determine the mechanism of nucleation and growth of martensite crystals, the size of thermal-induced martensite lamellae, the temperature Ms, and the temperature intervals of the martensitic transformation. In the as-grown single crystals, the high-temperature phase has only the L21-structure and the MT occurs at low (Ms = 125 K) temperatures due to the motion of the practically single interphase boundary in narrow temperature ranges of 3–7 K. The reduction in the volume fraction of the L21-phase to 40% and the formation of nanodomains (20–50 nm) of the L21-and B2-phases due to annealing at 1448 K for 1 h with quenching causes an increase in the MT temperatures by 80 K. The MT occurs in wide temperature ranges of 40–45 K because of multiple nucleation of individual large (300–500 µm) martensite lamellae and their growth. After aging at 773 K for 1 h, the precipitation of nanosized particles of the ω-phase in such a structure additionally increases the MT temperatures by 45 K. The MT occurs due to the multiple nucleation of packets of small (20–50 μm) martensite lamellae.

Ligand-Substitution-Induced Single-Crystal to Single-Crystal Transformations in a Redox-Versatile Cu(II) MOF toward Smartphone-Based Colorimetric Detection of Iodide.

Fabrication of a new three-dimensional Cu(II) metal-organic framework, {[Cu4(4,4'-bipy)3(OH)2(mal)3]·4H2O}n (1a; 4,4'-bipy = 4,4'-bipyridine, H2mal = malonic acid; P21/m), that undergoes an unprecedented redox-versatile ligand-substitution-induced single-crystal to single-crystal transformation, for smartphone-based detection of iodide was studied. The Cu-MOF 1a has been effortlessly synthesized by the microwave-heating technique. Phase formation of the Cu-MOF 1a depended on counter-anions. The transformations can be triggered by halides to corresponding coordination polymers through both non-redox and redox-associated pathways. The changes in the local structure and oxidation state of copper during the transformation were studied by ex situ and in situ synchrotron X-ray absorption spectroscopies. The selectivity of the halide-triggered transformation was investigated. A study on smartphone-based colorimetric detection of iodide was found to be linearly proportional to the iodide concentration in the range 10-1500 mg/L with a limit of detection of 5 mg/L and good precision relative standard deviation of 1.9% (n = 11), possibly to construct the iodide test kit.

Hydration-Facilitated Coordination Tuning of Metal-Organic Frameworks toward Water-Responsive Fluorescence and Proton Conduction.

Developing smart stimuli-responsive metal-organic frameworks (MOFs) with diversified induced readable signals is highly desirable; however, reported multimode responsive MOFs are always achieved under strong environmental stimulations, making it difficult to keep MOF structures stable for practical applications. Herein, we reported a hydration-facilitated coordination tuning strategy to achieve the dual-mode water response in fluorescence and proton conduction from a single MOF. The designed MOF permitted reversible single-crystal transformation via the controllable hydration effect on metal nodes. The change in coordination modes leads to the regulation on conformations of optical ligands, contributing to the switch of fluorescence emissions. Moreover, the hydration effect adds additional hydrogen-bond sites in channels and optimizes hydrogen-bond networks, abruptly enhancing the proton conductivity by ∼20 times. These results pave new avenues for the exploitation of smart MOFs with multimode responsive behavior for on-demand sensing/detection applications.

Single Crystal to Single Crystal Transformation of CuII Complexes Induced by Dehydrating and Hydrating of Ligands with Chroma Rewritable Behaviors.

In this work, the single crystal to single crystal (SCSC) transformations in three mononuclear copper complexes [CuL22]Cl2·2H2O (1), [CuL12Cl2] (2), and [CuL22]Cl2·4H2O (3) (L1 = di-2-pyridyl ketone, L2 = di(pyridin-2-yl)methanediol) are realized by the irreversible dehydration and hydration reaction of L1 and L2. Dark purple crystal 1 is obtained by self-assembly of L1 and CuCl2·2H2O in solvothermal reactions, in which the carbonyl group of L1 undergoes a hydration addition reaction to form L2. On heating, 1 transforms to 2 by dehydrating water accompanied by the change of the color and coordination octahedron of CuII ions. In a saturated water vapor environment, 2 can absorb six water molecules and transform to 3 with the same color and coordination environment with 1 but different lattice water. The SCSC process from 2 to 3 is reversible: 3 can transform back to 2 on heating like that of 1. Chroma rewritable behaviors in the structural transformation of the complexes make them visually identifiable temperature or water probes.

A phase-field model for interactive evolution of phase transformation and cracking in superelastic shape memory ceramics

This work presents a modified phase-field model for accurate coupling of phase transformation and cracking in shape memory ceramics. The existing phase-field models underestimate the elastic response at the beginning of the mechanical response. We modified the chemical free energy to control the rate of phase transformation and consequently obtain a physical elastic response before initiation of phase transformation. First, the forward and reverse martensitic phase transformation in a superelastic single crystal 3 mol% yttria-stabilized tetragonal zirconia is studied. Then, the interaction between phase transformation and fracture under displacement-controlled loading condition is investigated. The model predicts a realistic mechanical response and the experimentally observed microstructure and crack deflection due to the phase transformation. In addition, the model captures the reverse phase transformation and the stress drop due to the crack propagation.

Cu(hfac)2 Complexes with Acyclic Nitroxide Prone to Single-Crystal to Single-Crystal Transformation and Showing Mechanical Activity

Cu(hfac)₂ Complexes with Acyclic Nitroxide Prone to Single-Crystal to Single-Crystal Transformation and Showing Mechanical Activity

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane.

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C2H2- and C2H6-selective adsorption behavior, resulting in the potential tandem separation of C2H4 from C2H2 and C2H6 mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

Martensitic transformation in V3Si single crystal: 51V NMR evidence for coexistence of cubic and tetragonal phases

The Martensitic transformation (MT) in A15 binary-alloy superconductor V3Si, though studied extensively, has not yet been conclusively linked with a transition to superconductivity. Previous NMR studies have mainly been on powder samples and with little emphasis on temperature dependence during the transformation. Here we study a high-quality single crystal, where quadrupolar splitting of NMR spectra for 51V allowed us to distinguish between spectra from transverse chains of V as a function of temperature. Our data revealed that (1) the MT is not abrupt, but rather there is a microscopic coexistence of pre-transformed cubic phase and transformed tetragonal phase over a few K below and above Tm, while (2) no pre-transformed phase can be found at Tc, and (3) the Martensitic lengthening of one axis occurs predominantly in a plane perpendicular to the crystal growth axis, as twinned domains.

Dimensionality Mediated Highly Repeatable and Fast Transformation of Coordination Polymer Single Crystals for All-Optical Data Processing.

A family of coordination polymers (CPs) based on dynamic structural elements are of great fundamental and commercial interest addressing modern problems in controlled molecular separation, catalysis, and even data processing. Herein, the endurance and fast structural dynamics of such materials at ambient conditions are still a fundamental challenge. Here, we report on the design of a series of Cu-based CPs [Cu(bImB)Cl2] and [Cu(bImB)2Cl2] with flexible ligand bImB (1,4-bis(imidazol-1-yl)butane) packed into one- and two-dimensional (1D, 2D) structures demonstrating dimensionality mediated flexibility and reversible structural transformations. Using the laser pulses as a fast source of activation energy, we initiate CP heating followed by anisotropic thermal expansion and 0.2-0.8% volume changes with the record transformation rates from 2220 to 1640 s-1 for 1D and 2D CPs, respectively. The endurance over 103 cycles of structural transformations, achieved for the CPs at ambient conditions, allows demonstrating optical fiber integrated all-optical data processing.

Layered structures based on antimony tartrate dimers

Abstract Four complex metal antimony tartrates have been synthesized in single crystal form by slowly evaporating aqueous solutions of potassium antimony tartrate (tartar emetic) and metal nitrates or chlorides. Crystal structures of these compounds all contain infinite layers formed by linking antimony tartrate dimers with M–O bonds, with M = Li, La, Ce or Nd. Dehydration of the La and Ce compounds at elevated temperatures led to new layered structures via single-crystal to single-crystal transformations.

Scopariusicides D–M, ent-clerodane-based isomeric meroditerpenoids with a cyclobutane-fused γ/δ-lactone core from Isodon scoparius

Scopariusicides D–M (1–10), ten new ent-clerodane-based meroditerpenoids with a cyclobutane-fused γ/δ-lactone core, were isolated from Isodon scoparius. Their structures were determined by comprehensive analysis of spectroscopic data, single-crystal X-ray diffraction, chemical transformation, and TDDFT ECD calculation. A plausible biosynthetic pathway of 1–10 was proposed in which the asymmetrical cyclobutane ring was formed via a crossed “head-to-tail” intermolecular [2 + 2] cycloaddition in anti/syn facial approaches between an ent-clerodane lactone and a cis-4-hydroxycinnamic acid. Bioactivity evaluation manifested that 5 exhibited significant neuroprotective effect against corticosterone-induced injury in PC12 cells, while 6 and 7 exhibited moderate immunosuppressive activity against human T cell proliferation stimulated by anti-CD3/anti-CD28 mAb.

Reversible or irreversible: The photochromic behavior studies of ionic compound containing γ-octamolybdate and pyrazole ligands

Concrete structure and reliable performance are important advantages of polyoxometalate based materials. Herein, an ionic compound containing γ-octamolybdate and pyrazole ligands [(CH3)2NH2]4[Mo8O26(C3N2H4)2] (1) has been synthesized through a convenient method, and it manifests apparent photochromic characteristic under irradiation. The photochromic behavior studies of this compound show that the crystal can perform quasi-reversible single crystal to single crystal transformation, and the photochromic mechanism studies indicate that the redox of pyrazole ligand clearly relates to the photochromic process. Also, the photochromic studies of compound 1 in aqueous solution confirm this fact, and the high activity of pyrazole radical leads to the bleaching of photochromism and decomposition of compound 1, which makes the transfer irreversible in solution. By understanding the bleaching mechanism of aromatic ammonium γ-octamolybdate derivatives and the electron and proton transfer pathways in this process, more reliable photochromic materials based on polyoxometalate can be manufactured..

Shock-induced α" martensitic transformation in Nb single crystals

The structural and mechanical response of pure body-centered cubic (BCC) Nb under shock loading were systematically studied. Shock-induced orthorhombic (α") martensitic transformations were observed in single crystals Nb with different orientations, in which dense lenticular α" martensite variants distribute uniformly along different directions by forming a hierarchical structure. Neighbouring martensite variants share a {111}<110>α" twinning relationship between each other, and high-density dislocations are found distributing along the α"/BCC(β) interface. The formation of α" martensite was dominated by a mechanism of collinear shuffling of alternating {110}β planes along with <1 1¯ 0>β direction by a displacement δ. The collision between martensite variants along different direction induce abundant microcracks, with BCC-to-ω and BCC-to-FCC phase transformations occurring at the crack tips. These findings not only provide the experimental evidence of shock-induced α" martensitic transformation in pure BCC metals, but also link the microstructure interaction of materials to their macroscopic shock failure directly, which may have a broad impact on the study of shock deformation in different materials.

Front Cover: Supramolecular Assemblies and Reversible De‐/ Rehydration in One‐Dimensional Dimethyltin Carboxylates (Eur. J. Inorg. Chem. 13/2022)

The Front Cover shows the synthesis of one-dimensional ladder-like structures of dimethyltin carboxylates in an aqueous medium and highlights the role of chelating 2,2'-bipyridine to control the dimensionality in the presence of 1,2,4,5-benzenetetracarboxylate ligand. The structures reveal supramolecular assemblies formed by the inclusion of infinite water tapes [T4(0)A1] or the organic hydrate (bipy⋅6H2O). The study is a manifestation of reversible single crystal to single crystal structural transformation from P21/c to P212121 upon dehydration with conformational changes in the macrocycles. More information can be found in the Research Article by R. Shankar and co-workers.

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.

Polymorphism, Structure, and Nucleation of Cholesterol·H2O at Aqueous Interfaces and in Pathological Media: Revisited from a Computational Perspective.

We revisit the important issues of polymorphism, structure, and nucleation of cholesterol·H2O using first-principles calculations based on dispersion-augmented density functional theory. For the lesser known monoclinic polymorph, we obtain a fully extended H-bonded network in a structure akin to that of hexagonal ice. We show that the energy of the monoclinic and triclinic polymorphs is similar, strongly suggesting that kinetic and environmental effects play a significant role in determining polymorph nucleation. Furthermore, we find evidence in support of various O–H···O bonding motifs in both polymorphs that may result in hydroxyl disorder. We have been able to explain, via computation, why a single cholesterol bilayer in hydrated membranes always crystallizes in the monoclinic polymorph. We rationalize what we believe is a single-crystal to single-crystal transformation of the monoclinic form on increased interlayer growth beyond that of a single cholesterol bilayer, interleaved by a water bilayer. We show that the ice-like structure is also relevant to the related cholestanol·2H2O and stigmasterol·H2O crystals. The structure of stigmasterol hydrate both as a trilayer film at the air–water interface and as a macroscopic crystal further assists us in understanding the polymorphic and thermal behavior of cholesterol·H2O. Finally, we posit a possible role for one of the sterol esters in the crystallization of cholesterol·H2O in pathological environments, based on a composite of a crystalline bilayer of cholesteryl palmitate bound epitaxially as a nucleating agent to the monoclinic cholesterol·H2O form.

Halobenzene Clathrates of the Porous Metal-Organic Spin-Crossover Framework [Fe(tvp)2(NCS)2]n. Stabilization of a Four-Step Transition.

Here we show that the porous metal–organic spin crossover (SCO) framework [Fe(tvp)2(NCS)2]@4(CH3CN·H2O) [1@4(CH3CN·H2O)] is an excellent precursor material for the systematic synthesis, via single-crystal to single-crystal transformation, of a series of halobenzene clathrates. Immersion of samples constituted of single crystals of 1@4(CH3CN·H2O) in the liquid halobenzenes PhXn, X = F (n = 1–6), X = Cl (n = 1, 2), and X = Br (n = 1) at room temperature induces complete replacement of the guest molecules by PhXn to afford 1@2PhXn. Single-crystal analyses of the new clathrates confirm the integrity of the porous framework with the PhXn guests being organized by pairs via π-stacking filling the nanochannels. The magnetic and calorimetric data confirm the occurrence of practically complete SCO behavior in all of the clathrates. The characteristic SCO equilibrium temperatures, T1/2, seem to be the result of a subtle balance in the host–guest interactions, which are temperature- and spin-state-dependent. The radically distinct supramolecular organization of the PhCl2 guests in 1@2PhCl2 affords a rare example of four-step SCO behavior following the sequence [HS1:LS0] ↔ [HS2/3:LS1/3] ↔ [HS1/2:LS1/2] ↔ [HS1/4:LS3/4] ↔ [HS0:LS1], which has been structurally characterized.

Inclusion of CO2, NH3, SO2, Cl2 and H2S in porous N4O4-donor macrocyclic Schiff base

The removal and detection of highly toxic and environmentally harmful gases such as SO2, H2S and CO2 is a hot topic of the scientific community. Porous organic compounds, in particular, imine-based macrocycles, are promising materials for this purpose. In this paper we have used porous N4O4-donor macrocyclic Schiff base (1,6,20,25-tetraaza-2,5:8,9:17,18:21,24:27,28:36,37-hexabenzo-10,16,29,35-tetraoxa-cyclooctatriakonta-1,6,20,25-tetraen) (1) for sorption of NH3, SO2, Cl2, CO2 and H2S. Five novel inclusion compounds 1xNH3, 1xSO2, 1xCl2, 1xCO2 and 1xH2S were prepared by a single-crystal to single-crystal (SC-SC) transformation. Single-crystal X-ray diffraction (SCXRD) analysis of 1xCO2 and 1xNH3 inclusion compounds have shown that CO2 molecule resides in the plane of the macrocyclic ring connected by weak C–O … π interactions to the host, and no host-guest interactions in 1xNH3 were observed. The relative thermal stabilities of the host-guest systems (Ton – Tb parameter) is in the range from 93 (1xNH3) to 132 °C (1xH2S), indicating the formation of stable inclusion compounds. Although used gases are highly reactive and corrosive, FT-IR and powder diffraction studies indicate that the molecular and crystal structure of the host is constant upon gas sorption. The activated compound displays moderate uptake (0.35 mmol/g) of CO2 at 298 K. The relatively high thermal stability, constant molecular and crystal structure of inclusion compounds with interesting optical properties (determined by solid state UV–Vis) make this material potentially useful for the detection of toxic gases.

An Adaptive Hydrogen-Bonded Organic Framework for the Exclusive Recognition of p-Xylene.

Separation of xylene isomers is one of the most important but most challenging and energy-intensive separation processes in the petrochemical industry. Here, we report an adaptive hydrogen-bonded organic framework (HOF-29) constructed from a porphyrin based organic building block 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzonitrile (PTTBN), exhibiting the exclusive molecular recognition of p-xylene (pX) over its isomers of o-xylene (oX) and m-xylene (mX), as clearly demonstrated in the single crystal structure transformation and 1 H NMR studies. Single crystal structure studies show that single-crystal-to-single-crystal transformation from the as-synthesized HOF-29 to the pX exclusively included HOF-29⊃pX is triggered by the encapsulation of pX molecules, accompanied by sliding of the 2D layers and local distortion of the ligand, which provides multiple C-H⋅⋅⋅π interactions.