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A two-directional ferroelastic deformation in organic crystals is unprecedented owing to its anisotropic crystal packing, in contrast to isotropic symmetrical packing in inorganic compounds and polymers. Thereby, finding and constructing multidirectional ferroelastic deformations in organic compounds is undoubtedly complex and at once calls for deep comprehension. Herein, we demonstrate the first example of a two-directional ferroelastic deformation with a unique scissor-like movement in single crystals of trans-3-hexenedioic acid by the application of uniaxial compression stress. A detailed structural investigation of the mechanical deformation at the macroscopic and microscopic levels by three distinct force measurement techniques (including shear and three-point bending test), single crystal X-ray diffraction techniques, and polarized synchrotron-FTIR microspectroscopy highlighted that mechanical twinning promoted the deformation. The presence of two crystallographically equivalent faces and the herringbone arrangement promoted the two-directional ferroelastic deformation. In addition, anisotropic heat transfer properties in the parent and the deformed domains were investigated by thermal diffusivity measurement on all three axes using microscale temperature-wave analysis (µ-TWA). A correlation between the anisotropic structural arrangement and the difference in thermal diffusivity and mechanical behavior in the two-directional organoferroelastic deformation could be established. The structural and molecular level information from this two-directional ferroelastic deformation would lead to a more profound understanding of the structure-property relationship in multidirectional deformation in organic crystals.
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This study provides the first evidence that a Li ion can form ionic plastic crystals using crown ether with a bis-(trifluoromethanesulphonyl) amide (TFSA) anion. 1H, 7Li, and 13C nuclear-magnetic-resonance (NMR) measurements of the 15-crown-5-Li-TFSA complex revealed that the constituents underwent isotropic reorientation in the plastic crystalline phase. The NMR data of the 12-crown-4-Li-TFSA salt showed that the complex is a rotator crystal (the complexes are denoted as [Li 15C5] and [Li 12C4] in this paper). The X-ray diffraction (XRD) reflection patterns of the [Li 15C5] crystal recorded in the highest-temperature solid phase (plastic phase) could be indexed to a cubic structure. Conversely, [Li 12C4] could be fitted to a trigonal structure. In this study, [M (3n)Cn] (M = Li, Na, K; n = 4-6) complexes were also prepared, and NMR, DSC, XRD, and electrical conductivity measurements were performed. Based on these results, we additionally revealed that the [Na 15C5] and [K (15C5)2] complexes are also new rotator crystals. Single-crystal XRD measurements also revealed that the [Na 15C5] compound has two stable sites in the crystal. Activation energies of molecular motions in the [M (3n)Cn] crystals were estimated using 1H NMR relaxation time (T1 and T2) measurements. The electrical conductivity measurements of [Li 12C4], [Li 15C5], and [Na 15C5] showed high ionic conductivities (â¼10-2 S cm-1).
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Mechanical twinning changes atomic, molecular, and crystal orientations along with directions of the anisotropic properties of the crystalline materials while maintaining single crystallinity in each domain. However, such deformability has been less studied in brittle organic crystals despite their remarkable anisotropic functions. Herein we demonstrate a direction-dependent mechanical twinning that shows superelasticity in one direction and ferroelasticity in two other directions in a single crystal of 1,3-bis(4-methoxyphenyl)urea. The crystal can undergo stepwise twinning and ferroelastically forms various shapes with multiple domains oriented in different directions, thereby affording a crystal that shows superelasticity in multiple directions. This adaptability and shape recoverability in a ferroelastic and superelastic single crystal under ambient conditions are of great importance in future applications of organic crystals as mechanical materials, such as in soft robotics.
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Ferroelasticity has been reported for several types of molecular crystals, which show mechanical-stress-induced shape change under twinning and/or spontaneous formation of strain. Aiming to create materials that exhibit both ferroelasticity and light-emission characteristics, we discovered the first examples of ferroelastic luminescent organometallic crystals. Crystals of arylgold(I)(N-heterocyclic carbene)(NHC) complexes bend upon exposure to anisotropic mechanical stress. X-ray diffraction analyses and stress-strain measurements on these ferroelastic crystals confirmed typical ferroelastic behavior, mechanical twinning, and the spontaneous build-up of strain. A comparison with single-crystal structures of related gold-NHC complexes that do not show ferroelasticity shed light on the structural origins of the ferroelastic behavior.
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As altering permanent shapes without loss of material function is of practical importance for material molding, especially for elastic materials, shape-rememorization ability would enhance the utility of elastic crystalline materials. Since diffusionless plastic deformability can preserve the crystallinity of materials, the interconversion of diffusionless mechanical deformability between superelasticity and ferroelasticity could enable shape rememorization of superelastic single crystals. This study demonstrates the shape rememorization of an organosuperelastic single crystal of 1,4-dicyanobenzene through time-reversible interconversion of superelasticity-ferroelasticity relaxation by holding the mechanically twinned crystal without heating. The shape-rememorization ability of the organosuperelastic crystal indicates the compatibility of superelasticity (antiferroelasticity) and ferroelasticity as well as the intrinsic workability of organic crystalline materials capable of recovering their crystal functions under mild conditions.
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A single crystal of adipic acid shows twinning ferroelasticity by the reversible molecular conformational change. The flexible nature of components in molecular solids raises the efficiency of energy dissipation using organoferroelasticity.
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Ferroelasticity involves the generation of spontaneous strain in a solid by the application of mechanical stress. The phenomenon has been well-studied in metal alloys but relatively neglected in organic solid-state chemistry. Herein we present multiple discrete modes of mechanical twinning and a mechanistic analysis of ferroelasticity in 1,4-diethoxybenzene. Single crystals of the compound can be almost freely deformed, as multiple different twin domains are generated simultaneously. Within each domain, single-crystal character is preserved. Such extremely versatile, ferroelastic deformability is unprecedented in single crystals of any kind and defies the fragility and anisotropic mechanical behaviour of most organic crystals. The dissipated energy and critical stress associated with twinning deformation in 1,4-diethoxybenzene suggests that organic solids could be developed for absorbing weak mechanical shocks in such applications as mechanical damping and soft robotics.
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Ferroelasticity has been relatively well-studied in mechanically robust inorganic atomic solids but poorly investigated in organic crystals, which are typically inherently fragile. The absence of precise methods for the mechanical analysis of small crystals has, no doubt, impeded research on organic ferroelasticity. The first example of ferroelasticity in an organic molecular crystal of 5-chloro-2-nitroaniline is presented, with thorough characterization by macro- and microscopic methods. The observed cyclic stress-strain curve satisfies the requirements of ferroelasticity. Single-crystal X-ray structure analysis provides insight into lattice correspondence at the twining interface, which enables substantial crystal bending by a large molecular orientational shift. This deformation represents the highest maximum strain (115.9 %) among reported twinning materials, and the associated dissipated energy density of 216â kJ m-3 is relatively large, which suggests that this material is potentially useful as a mechanical damping agent.
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In solid-state science, most changing phenomena have been mysterious. Furthermore, the changes in chemical composition should be added to mere physical changes to also cover the chemical changes. Here, the first success in characterizing the nature of gas inclusion in a single crystal is reported. The gas inclusion process has been thoroughly investigated by inâ situ optical microscopy, single-crystal X-ray diffraction analyses, and gas adsorption measurements. The results demonstrated an inclusion action of a first-order transition behavior induced by a critical concentration on the phase boundary. The transfer of phase boundary and included gas are strongly related. This relationship can generate the dynamic features hidden in the inclusion phenomena, which can lead to the guest capturing and transfer mechanism that can apply to spatiotemporal inclusion applications by using host solids.
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Gases/química , Complexos de Coordenação/química , Cobre/química , Cristalização , Difusão , Etanol/química , Transição de Fase , Difração de Raios XRESUMO
Generally, superelastic behavior cannot be expected in mechanically twinned crystals because there is essentially no strain on the interface that is a driving force for spontaneous shape recovery. However, we found that single crystals of 3,5-difluorobenzoic acid are superelastic organic crystals under mechanical twinning. The unexpected shape recovery can be explained by molecular distortion on the twinning interface, which suggests a new mechanism for superelasticity in molecular materials.
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Ácido Benzoico/química , Cristalografia por Raios X , Elasticidade , Conformação MolecularRESUMO
A novel single-crystal membrane [Cu(II)2(4-F-bza)4(2-mpyz)]n (4-F-bza = 4-fluorobenzoate; 2-mpyz = 2-methylpyrazine) was synthesized and its identical permeability in any crystal direction in the correction for tortuosity proved that gas diffuses inside the channels without detour. H2 permeated by 1.18 × 10(-12) mol m m(-2) s(-1) Pa(-1) with a high selectivity (Fα: 23.5 for H2/CO and 48.0 for H2/CH4) through its 2D-channels having a minimum diameter of 2.6 Å, which is narrower than the Lennard-Jones diameter of H2 (2.827 Å), CO (3.690 Å), and CH4 (3.758 Å). The high rate of permeation was well explained by a modified Knudsen diffusion model based on the space expansion effect, which agrees with the observed permselectivity enhanced for smaller gases in considering the expansion of a channel resulting from the collision of gas molecules or atoms onto the channel wall. An analysis of single-crystal X-ray data showed the expansion order to be H2 > Ar > CH4, which was expected from the permeation analysis. The permselectivity of a porous solid depends on the elasticity of the pores as well as on the diameter of the vacant channel and the size of the target gas.
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Benzoatos/química , Cobre/química , Gases/química , Membranas Artificiais , Benzoatos/síntese química , Monóxido de Carbono/química , Cristalografia por Raios X , Difusão , Hidrogênio/química , Metano/química , Modelos Moleculares , Permeabilidade , Pirazinas/síntese química , Pirazinas/químicaRESUMO
Superelastic materials (crystal-to-crystal transformation pseudo elasticity) that consist of organic components have not been observed since superelasticity was discovered in a Au-Cd alloy in 1932. Superelastic materials have been exclusively developed in metallic or inorganic covalent solids, as represented by Ti-Ni alloys. Organosuperelasticity is now revealed in a pure organic crystal of terephthalamide, which precisely produces a large motion with high repetition and high energy storage efficiency. This process is driven by a small shear stress owing to the low density of strain energy related to the low lattice energy.
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Ftalimidas/química , Cristalização , Elasticidade , Transição de Fase , TermodinâmicaRESUMO
We report an unprecedented result of self-aggregation of [Pt(L1 )Cl] (HL1 =1,3-di(5-carboxy-2-pyridyl)benzene) triggered by CO2 in basic aqueous solution. The color of basic aqueous solution containing [Pt(L1 )Cl] changes from yellow to blue-green during the aggregation resulted from a reaction with CO2 in air. Upon CO2 gas bubbling, strong and broad absorption bands of aggregate assigned to the metal-metal-to-ligand charge-transfer transition appeared at 701 and 1152â nm. Recrystallization of [Pt(L1 )Cl] from Na2 CO3 aqueous solution afforded polymorphic crystals of red and blue-green forms. A single X-ray crystallography revealed that the red form of crystal consists of a Pt-Pt stacked dimer bridged by CO3 2- ion and one of the carboxy groups of L1 is deprotonated. An elemental analysis provided evidence that the blue-green crystal is constructed by linear array consisting of the [Pt(L2 )(CO3 )]3- (HL2 =1,3-di(5-carboxylate-2-pyridyl)benzene) units. The formation process of blue-green aggregate in aqueous solution was monitored through a transient absorption spectrum, and the absorption of aggregates involved in the spectral change were examined by a global analysis. A singular value decomposition and kinetic analysis provide that there are four species resulted from the self-assembling reaction in the solution and the maximal degree of aggregation is at least 32-mer.
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Although the finding of superelasticity and ferroelasticity in organic crystals has been serendipitous, an increasing number of organic crystals with such deformation properties have been witnessed. Understanding the structure-property relationship can aid in the rational selection of intermolecular interactions to design organic crystals with desired superelastic or ferroelastic properties. In this study, we investigated the mechanical deformation in two cocrystals, prepared with the parent compound, 1,4-diiodotetrafluorobenzene with two coformers, 1,2-bis(4-pyridyl)ethane and pyrene. The parent compound and coformers were chosen to introduce distinct weak interactions such as halogen bonds and C-Hâ¯F, and πâ¯π interactions in the crystal structure. The two cocrystals exhibited different mechanical deformations, superelasticity, and ferroelasticity, respectively. The single-crystal X-ray diffraction and energy framework analysis of the crystal structure of the cocrystals revealed that both deformations were caused by mechanical twinning. Interestingly, a difference in the extent of deformation was observed, modulated by a combination of strong and weak intermolecular interactions in the superelastic cocrystal, and only weak interaction in the ferroelastic one. In this comparison, the superelastic cocrystal exhibited higher thermal diffusivity than the ferroelastic cocrystal, indicating the presence of symmetrical and relatively robust intermolecular interactions in the superelastic cocrystal.
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Molecular crystals of Pt(II) complexes with metallophilic interactions can provide bright assembly-induced luminescence with colour tunability. However, the brittleness of many of these crystals makes their application in flexible optical materials difficult. Herein, we have achieved the elastic deformation of crystals of polyhalogenated Pt(II) complexes exhibiting bright assembly-induced luminescence. A crystal of [Pt(bpic)(dFppy)] (Hbpic = 5-bromopicolinic acid, HdFppy = 2-(2,4-difluorophenyl)pyridine) and a co-crystal of [Pt(bpic)(dFppy)] and [Pt(bpic)(ppy)] (Hppy = 2-phenylpyridine) were found to exhibit significant elastic deformation due to their highly anisotropic interaction topologies. While the crystal of [Pt(bpic)(dFppy)] exhibited monomer-based ligand-centred 3ππ* emission with an emission quantum yield of 0.40, the co-crystal exhibited bright, triplet metal-metal-to-ligand charge transfer (3MMLCT) emission owing to Ptâ¯Pt interactions, thereby achieving a significantly higher emission quantum yield of 0.94.
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Shape-memory materials can be mechanically deformed and subsequently reverse the deformation upon changing the temperature. Shape-memory materials have attracted considerable attention for basic research and industrial applications, and polymer and alloy shape-memory materials have been well studied; however, it is formidably challenging to develop functional shape-memory materials, such as materials with multi-stage and anisotropic shape changes and shape changes accompanied by changes in color and light emission. Here, we found a reversible multi-stage shape-changing effect after mechanical deformation in a molecular crystal induced by multi-step thermal phase transitions with reversible shape changes and luminescence-color changes. Using single-crystal structure and thermal analyses as well as mechanical property measurements, we found that the reversible multi-stage shape-changing effect was achieved by a combination of a twinning deformation and multi-step thermal phase transitions. The changes in the crystal shape and luminescence suggest novel strategies for imparting known shape-memory materials with additional functionalities.
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Development of gas separation materials has been one of the basic requirements of industry. Microporous materials have adequate pores for gas separation and have contributed to the advancement of gas purification techniques. Because the simplest and most economical method would be membrane separation, various microporous membranes have been prepared and explored for their separation properties. However, a key issue remains as to how to generate defect-free membranes with practical gas permeance. Here we report the preparation of a well-oriented single-crystal membrane with high permeance by using a flexible single crystal of [Cu(2)(bza)(4)(pyz)](n) possessing one-dimensional (1D) penetration channels; this membrane exhibits anisotropic gas permeation through the 1D channels with high permselectivity for H(2) and CO(2). Although the diameter of the neck of the narrow channels is smaller than the kinetic diameters of the sample gases, various gases pass through the 1D channels. This report provides a new way of developing gas permeation membranes as sophisticated crystal devices for gas purification techniques.
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Cobre/química , Gases/química , Membranas Artificiais , Compostos Organometálicos/química , Cristalografia por Raios X , Cinética , Modelos Moleculares , Estrutura Molecular , Propriedades de SuperfícieRESUMO
For the purpose of investigating the correlation between host gas adsorption ability and structural flexibility, the combination of metal benzoate complexes [M(II)(2)(bza)(4)] (M(II) = Rh (a), Cu (b); bza = benzoate) and pyrazine derivatives (pyz = pyrazine (1), 2-mpyz = 2-methylpyrazine (2), 2,3-dmpyz = 2,3-dimethylpyrazine (3)) yields a series of one-dimensionally assembled complexes. The study of the adsorption properties of this series was examined for CO(2), H(2), N(2), O(2), and Ar gases at 195 K (CO(2)) or at 77 K (all others). The adsorption manners of these complexes are similar for each gas, while the pressure at which adsorption started or rapidly grew increased with a rise in the number of methyl groups in the case of adsorbable gases. The maximum amount of adsorption was a positive integer, e.g., 3 molecules per M(2) unit for 1 and 2 and 2 molecules per M(2) unit for 3 in the case of CO(2) adsorption for all complexes at 0.1 MPa of adsorbable gases. Structural transformation was observed accompanying gas adsorption. This transformation was observed when the adsorption amount reached 1 molecule per M(2) unit, suggesting a correlation of the adsorption amount and dynamic adsorption behavior. Single-crystal X-ray analyses of nonincluded crystals and CO(2) inclusions for all hosts (1-3) revealed that large structural changes occurred through CO(2) adsorption to increase the inner space for adsorption gases, depending on the substituents on the pyrazine ring. These facts were confirmed as a transition by DSC measurements using a mixed CO(2)/N(2) gas atmosphere. Solid-state (1)H and (2)H NMR studies of the crystalline sample of 1a and its partially deuterated samples of 1a' (deuterated phenyl group) and 1a'' (deuterated pyrazine) revealed rapid 180 degree-flip motions of the aromatic rings of the host skeletons, which form the walls of the channels. These "rotating" motions would help the diffusion of CO(2) molecules through a narrow channel at relatively low pressure. Indeed, the motions of phenyl groups and methyl-substituted pyrazine moieties of phenyl deuterated 3a were confirmed to be very slow by solid-state (1)H and (2)H NMR spectra, where the amount of adsorbed gas molecules was small for 3a at 0.1 MPa of CO(2).
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Benzoatos/química , Dióxido de Carbono/química , Cobre/química , Movimento (Física) , Compostos Organometálicos/química , Pirazinas/química , Ródio/química , Adsorção , Cristalografia por Raios X , Efeito Estufa , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação Molecular , TemperaturaRESUMO
Chromism-color changes by external stimuli-has been intensively studied to develop smart materials because of easily detectability of the stimuli by eye or common spectroscopy as color changes. Luminescent chromism has particularly attracted research interest because of its high sensitivity. The color changes typically proceed in a one-way, two-state cycle, i.e. a stimulus-induced state will restore the initial state by another stimuli. Chromic systems showing instant, biphasic color switching and spontaneous reversibility will have wider practical applicability. Here we report luminescent chromism having such characteristics shown by mechanically controllable phase transitions in a luminescent organosuperelastic crystal. In mechanochromic luminescence, superelasticity-diffusion-less plastic deformation with spontaneous shape recoverability-enables real-time, reversible, and stepless control of the abundance ratio of biphasic color emissions via a single-crystal-to-single-crystal transformation by controlling a single stimulus, force stress. The unique chromic system, referred to as superelastochromism, holds potential for realizing informative molecule-based mechanical sensing.
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Mechanically adaptable molecular crystals have potential applications in flexible smart materials and devices. Here, we report the mechanism of plastic deformation in single crystals of a small organic molecule (N-(4-ethynylphenyl)-3-fluoro-4-(trifluoromethyl)benzamide) that can be repeatedly irreversibly bent and returned to its original shape without concomitant delamination or loss of integrity. Along with the quantification of the crystals' local and bulk mechanical properties (hardness, indentation modulus and Young's modulus), micro-focus synchrotron X-ray diffraction mapping show that upon deformation, molecular layers lined with trifluoromethyl groups cooperatively slip past one another resulting in their impressive plastic malleability.