Reversible Solid-state Transformation Research Articles

Strong d-π Orbital Coupling of Co-C4 Atomic Sites on Graphdiyne Boosts Potassium-Sulfur Battery Electrocatalysis.

Potassium-sulfur (K-S) batteries are severely limited by the sluggish kinetics of the solid-phase conversion of K2S3/K2S2 to K2S, the rate-determining and performance-governing step, which urgently requires a cathode with facilitated sulfur accommodation and improved catalytic efficiency. To this end, we leverage the orbital-coupling approach and herein report a strong d-π coupling catalytic configuration of single-atom Co anchored between two alkynyls of graphdiyne (Co-GDY). The d-π orbital coupling of the Co-C4 moiety fully redistributes electrons two-dimensionally across the GDY, and as a result, drastically accelerates the solid-phase K2S3/K2S2 to K2S conversion and enhances the adsorption of sulfur species. Applied as the cathode, the S/Co-GDY delivered a record-high rate performance of 496.0 mAh g-1 at 5 A g-1 in K-S batteries. In situ and ex situ characterizations coupling density functional theory (DFT) calculations rationalize how the strong d-π orbital coupling of Co-C4 configuration promotes the reversible solid-state transformation kinetics of potassium polysulfide for high-performance K-S batteries.

A Rod-Packing Hydrogen-Bonded Organic Framework with Suitable Pore Confinement for Benchmark Ethane/Ethylene Separation.

For the separation of ethane from ethylene, it remains challenging to target both high C2 H6 adsorption and selectivity in a C2 H6 -selective material. Herein, we report a reversible solid-state transformation in a labile hydrogen-bonded organic framework to generate a new rod-packing desolvated framework (ZJU-HOF-1) with suitable cavity spaces and functional surfaces to optimally interact with C2 H6 . ZJU-HOF-1 thus exhibits simultaneously high C2 H6 uptake (88 cm3 g-1 at 0.5 bar and 298 K) and C2 H6 /C2 H4 selectivity (2.25), which are significantly higher than those of most top-performing materials. Theoretical calculations revealed that the cage-like cavities and functional sites synergistically "match" better with C2 H6 to provide stronger multipoint interactions with C2 H6 than C2 H4 . In combination with its high stability and ultralow water uptake, this material can efficiently capture C2 H6 from 50/50 C2 H6 /C2 H4 mixtures in ambient conditions under 60 % RH, providing a record polymer-grade C2 H4 productivity of 0.98 mmol g-1 .

A Mechanism for Reversible Solid-State Transitions Involving Nitro Torsion

Reversible solid-state transformations are important in stimuli-responsive materials. The current understanding is limited on what kind of structure enables reversible transitions. We report that f...

Entropy-Stabilized Oxides owning Fluorite Structure obtained by Hydrothermal Treatment

Entropy-Stabilized Oxides (ESO) is a modern class of multicomponent advanced ceramic materials with attractive functional properties. Through a five-component oxide formulation, the configurational entropy is used to drive the phase stabilization over a reversible solid-state transformation from a multiphase to a single-phase state. In this paper, a new transition metal/rare earth entropy-stabilized oxide, with composition Ce0.2Zr0.2Y0.2Gd0.2La0.2O2−δ, was found after several investigations on alternative candidate systems. X-Ray Diffraction (XRD) analyses of calcined powders pointed out different behavior as a function of the composition and a single-phase fluorite structure was obtained after a specific thermal treatment at 1500 °C. Powders presented the absence of agglomeration, so that the sintered specimen exhibited sufficient densification with a small porosity, uniformly distributed in the sample.

Structural, Magnetic, and Optical Studies of the Polymorphic 9'-Anthracenyl Dithiadiazolyl Radical.

The fluorescent 9'-anthracenyl-functionalized dithiadiazolyl radical (3) exhibits four structurally determined crystalline phases, all of which are monomeric in the solid state. Polymorph 3α (monoclinic P21/ c, Z' = 2) is isolated when the radical is condensed onto a cold substrate (enthalpically favored polymorph), whereas 3β (orthorhombic P21 21 21, Z' = 3) is collected on a warm substrate (entropically favored polymorph). The α and β polymorphs exhibit chemically distinct structures with 3α exhibiting face-to-face π-π interactions between anthracenyl groups, while 3β exhibits edge-to-face π-π interactions. 3α undergoes an irreversible conversion to 3β on warming to 120 °C (393 K). The β-phase undergoes a series of reversible solid-state transformations on cooling; below 300 K a phase transition occurs to form 3γ (monoclinic P21/ c, Z' = 1), and on further cooling below 165 K, a further transition is observed to 3δ (monoclinic P21/ n, Z' = 2). Both 3β → 3γ and 3γ → 3δ transitions are reversible (single-crystal X-ray diffraction), and the 3γ → 3δ process exhibits thermal hysteresis with a clear feature observed by heat capacity measurements. Heating 3β above 160 °C generates a fifth polymorph (3ε) which is distinct from 3α-3δ based on powder X-ray diffraction data. The magnetic behavior of both 3α and the 3β/3γ/3δ system reflect an S = 1/2 paramagnet with weak antiferromagnetic coupling. The reversible 3δ ↔ 3γ phase transition exhibits thermal hysteresis of 20 K. Below 50 K, the value of χm T for 3δ approaches 0 emu·K·mol-1 consistent with formation of a gapped state with an S = 0 ground-state configuration. In solution, both paramagnetic 3 and diamagnetic [3][GaCl4] exhibit similar absorption and emission profiles reflecting similar absorption and emission mechanisms for paramagnetic and diamagnetic forms. Both emit in the deep-blue region of the visible spectrum (λem ∼ 440 nm) upon excitation at 255 nm with quantum yields of 4% (3) and 30% ([3][GaCl4]) affording a switching ratio [ΦF(3+)/ΦF(3)] of 7.5 in quantum efficiency with oxidation state. Solid-state films of both 3 and [3][GaCl4] exhibit emission bands at a longer wavelength (490 nm) attributed to excimer emission.

Solid state transformations of different stoichiometric forms of an organic salt formed from 5-sulfosalicylic acid and hexamethylenetetramine upon dehydration and rehydration

The reversible solid state transformations between the diverse forms (e.g. hydrous/anhydrous and different stoichiometries) of a salt formed from 5-sulfosalicylic acid (A) and hexamethylenetetramine (B) have been investigated.

Thermally induced reversible solid-state transformation of novel s-indacene 1,3,5,7-tetraone derivatives

Novel electronically efficient s-indacene 1,3,5,7-tetraone derivatives were synthesized, which exhibit unique thermally induced polymorphic transformation.

Entropy-stabilized oxides.

Configurational disorder can be compositionally engineered into mixed oxide by populating a single sublattice with many distinct cations. The formulations promote novel and entropy-stabilized forms of crystalline matter where metal cations are incorporated in new ways. Here, through rigorous experiments, a simple thermodynamic model, and a five-component oxide formulation, we demonstrate beyond reasonable doubt that entropy predominates the thermodynamic landscape, and drives a reversible solid-state transformation between a multiphase and single-phase state. In the latter, cation distributions are proven to be random and homogeneous. The findings validate the hypothesis that deliberate configurational disorder provides an orthogonal strategy to imagine and discover new phases of crystalline matter and untapped opportunities for property engineering.

Polymorphism of Nifedipine: Crystal Structure and Reversible Transition of the Metastable β Polymorph

We report the first structural determination of the metastable β polymorph of nifedipine (NIF) by single-crystal X-ray diffraction. Stable, high-quality crystals were grown from the melt in the presence of a polymer dopant. Our β NIF structure is characterized by a unit cell similar to that of the structure recently proposed from powder diffraction, but significantly different molecular conformations. Unlike the stable α polymorph, β NIF undergoes a reversible solid-state transformation near 60 °C. The now available β NIF structure clarifies some confusion concerning NIF polymorphs and enables inquiries into the structural basis for the selective crystallization of β NIF from glasses. We report that another polymorph crystallizes concomitantly with β NIF from the supercooled melt and transforms to β NIF at room temperature; this polymorph also undergoes reversible solid-state transformation.

Polymeric fullerene chains in RbC60 and KC60

NEARLY all of the molecular crystals containing C60, formed at ambient pressure1,2 have inter-fullerene separations of the order of 10 A — the expected distance based on the molecular van der Waals radii. The sole exceptions are the room-temperature phases of AC60 (where A denotes K, Rb or Cs), which are formed by reversible solid-state transformation from high-temperature (>150 °C) phases3. These phases have lattice parameters about 9% shorter in one direction, and in addition RbC60 has magnetic properties suggestive of a one-dimensional metal4. We suggested in ref. 4 that this short distance may be due to covalent bonding between neighbouring C60 molecules. Here we provide direct evidence for such bonding from powder X-ray diffraction studies of RbC60 and KC60 . The linkage is through a [2+2] cycloaddition, which has been hypothesized to take place during photopolymerization of solid C60 (ref. 5), and which has also been proposed6 for RbC60. Such inter-fullerene linkages are calculated7,8 to be the preferred mode of dimerization of C60. The AC60 phases thus provide an example of a thermal phase transition driven by the reversible formation and breaking of covalent bonds.

A Novel Synthesis of N-Styryl Heterocycles

Reaction of the anions of a variety of 2-carboethoxy N-heterocycles with styrene oxide yields directly the N-(trans-2-styryl)-2-carboxylic acids. The reaction has been shown to proceed through a lactone intermediate which undergoes rapid elimination to form the unsaturated acid. The reaction has been used to alkylate 2-carboethoxy pyrrole, diethyl pyrazole-3,5-dicarboxylate, ethyl indole-2-carboxylate, ethyl benzimidazole-2-carboxylate, and ethyl 2-pyrrolidone-5-carboxylate. Yields were 82, 88, 93.5, 57, and 5% respectively.1-(trans-2-Styryl)benzirnidazole-2-carboxylic acid of m.p. 75–77 °C undergoes an interesting, reversible solid-state transformation to a high melting (255–260 °C), presumably zwitterionic, form.

A New Reversible Solid-State Transformation in Iron–Nickel Alloys in the Invar Range of Compositions

A New Reversible Solid-State Transformation in Iron–Nickel Alloys in the Invar Range of Compositions