Coordination polymers, including metal-organic frameworks, are a diverse class of materials with myriad properties and potential applications. However, a number of drawbacks have hindered the scaling ...up of such materials towards commercial applications. These include health and safety risks, environmental hazards, poor cost efficiency and sustainability shortfalls. In contrast to the systematic progress of organic green chemistry, which has contributed to improvements in the sustainability of chemical processing, the development of green chemistry in the context of coordination polymers has been fragmented and sporadic. This review describes advances in the use of green components: benign sustainable ligands and non-hazardous earth abundant metals. Additionally, solvent considerations, synthesis strategies for improved sustainability and the performance of coordination polymers relative to alternative competing materials are discussed.
A perspective on the development of coordination polymers based on sustainable benign ligands and metals, and green synthesis.
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.
Twinning ways: Ferroelastic single crystals of 1,4‐diethoxybenzene can be almost freely deformed by simultaneously accessing multiple modes of mechanical twinning. Within each twin 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.
Phase diagram mapping is a useful method for predicting and rationalizing unusual thermally and mechanically triggered crystal transition phenomena. Here we focus on crystals of pimelic acid, which ...is known to exist as at least three polymorphs: modifications I–III. Modification III exhibits twinning ferroelasticity and a polymorphic transition, involving superelastic behavior by shearing. Additionally, a phase transition from modification III to modification II by heating involves a rapid expansion of crystals. The reverse transition from the metastable modification II to the thermally stable modification III at ambient temperature by mechanical stimuli involves rapid shrinkage, causing crystals to jump or rapidly fragment. For the first time a comprehensive phase diagram has been presented that accounts for the three different mechanical responses observed for pimelic acid: jumping/fragmentation, superelasticity, and ferroelasticity. Both thermal and mechanical transitions have been rationally mapped on the phase diagram.
A non‐interpenetrated metal–organic framework with a paddle‐wheel secondary building unit has been activated by direct thermal evacuation, guest exchange with a volatile solvent, and supercritical ...CO2 drying. Conventional thermal activation yields a mixture of crystalline phases and some amorphous content. Exchange with a volatile solvent prior to vacuum activation produces a pure breathing phase with high sorption capacity, selectivity for CO2 over N2 and CH4, and substantial hysteresis. Supercritical drying can be used to access a guest‐free open phase. Pressure‐resolved differential scanning calorimetry was used to confirm and investigate a systematic loss of sorption capacity by the breathing phase as a function of successive cycles of sorption and desorption. A corresponding loss of sample integrity was not detectable by powder X‐ray diffraction analysis. This may be an important factor to consider in cases where flexible MOFs are earmarked for industrial applications.
Taking a deep breath: A metal–organic framework with a paddle‐wheel secondary building unit is activated by direct thermal evacuation, guest exchange with a volatile solvent, and supercritical CO2 drying. The solvent exchange step produces a pure breathing phase with high sorption capacity, selectivity for CO2 over N2 and CH4, and substantial hysteresis.
Specific kinds of alloys, so-called shape-memory alloys (SMAs), show superelasticity. Their mechanism has been known as slight atomic rearrangement by keeping relative positional relationships. ...Contrary to this, not only molecular rearrangement but also orientational and conformational changes are involved in superelasticity in molecular single crystals. Herein, we investigate superelasticity correlated with molecular bending in a crystal formed by a one-dimensional hydrogen-bonding supramolecular chain of pimelic acid. Because of the structural analogy of the supramolecular chain and polyethylene as one of the linear covalent polymers, the bending mechanism has a possibility of being applied to the similar deformability in the crystalline polymer solids. According to single-crystal X-ray structural analyses, the superelasticity based on mechanical generation and spontaneous dissipation of a thermodynamically unstable phase is induced by bending of the molecular chains along with a normal stress effect based on conformation changes via precession movement.
The control of coercive stress in organoferroelasticity is demonstrated in single crystals of trans -1,4-cyclohexanedicarboxylic acid with bulky cyclohexane rings. Flipping difficulty, due to the ...bulkiness, increased coercive stress, which can improve mechanical damping. Crystals also undergo the spontaneous disappearance of a twinned domain upon unloading before the completion of domain formation.
A nitromethane solvate of 18-crown-6 was investigated by means of variable-temperature single-crystal X-ray diffraction in response to a report of abnormal unit cell contraction. Exceptionally large ...positive thermal expansion in two axial directions and negative thermal expansion along the third was confirmed. The underlying mechanism relies exclusively on weak electrostatic interactions to yield a linear thermal expansion coefficient of -129 × 10(-6) K(-1), the largest negative value yet observed for an organic inclusion compound.
It is demonstrated that guest replacement in a series of isoskeletal organic inclusion compounds can produce drastic changes in thermal expansion behavior. The compounds 1, 2, and 3 have 18-crown-6 ...as host molecule and nitromethane, acetonitrile, and iodomethane, respectively, as guests. Along the principal axis X1 the linear component of thermal expansion is negative for 1 and 2 but positive for 3. All three compounds have varying degrees of large volumetric thermal expansion, with coefficients of 378(22), 226(3), and 256(8) × 10–6 K–1 for 1, 2, and 3, respectively. Crystal structure analysis and computational methods were used to elucidate general features of the underlying mechanism of thermal expansion for the series. The contributions of several factors are described, including host–guest compatibility, electrostatic effects, and steric effects. A tilting mechanism gives rise to the negative components of thermal expansion in 1 and 2 but is inhibited by the large molecular volume of the guest in 3. In addition, the thermosalient effect was observed for 2. To our knowledge this is the first example of thermosalience reported for an inclusion compound.
We demonstrate exceptional twinning deformation in a molecular crystal upon application of mechanical stress. Crystal integrity is preserved and the deformation is associated with a large bending ...angle (65.44°). This is a new strategy to increase the magnitude of the dissipated energy in an organic solid comparable to that seen in alloys. By X-ray crystallographic analysis it was determined that a large molecular rearrangement at the twinning interface preserves the crystal integrity. Drastic molecular rearrangement at the twinning interface helps to preserve hydrogen bonding in the molecular rotation, which facilitates the large bending angle. The maximum shear strain of 218.81% and dissipated energy density of 1 MJ m
can significantly enhance mechanical damping of vibrations.
A five-fold interpenetrated metal organic framework (MOF) has been shown to exhibit anomalous thermal expansion due to the combined effect of hinge-like motion and sliding of individual diamondoid ...networks. Upon dehydration, the MOF undergoes dramatic structural changes, thereby altering its thermal expansion behaviour to a large extent.
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