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Understanding the microscopic origin of phase transitions in hybrid crystals is of significant important but challenging for designing novel phase‐transition materials. Here, three new hybrid crystals, (Me3NR)4[Ni(NCS)6] (R=ethyl for 1, propyl for 2, and butyl for 3) were synthesized and comprehensively studied on their crystal structures, intermolecular interactions, and phase transitions. They possess a same anti‐XeF4 structure mode but exhibit different phase transitions arising from their subtly changed alkyl groups. Specifically, 1 undergoes four‐step P21/c‐P21/c‐P21/c‐Pbca‐Cmce crystalline transitions at 165, 203, 244, and 280 K, respectively; 2 undergoes three‐step P212121‐Pbca‐P21/n‐P3‾ ${\bar 3}$ 1c crystalline transitions at 167, 393, and 410 K, respectively, following by a solid‐liquid transition at 453 K; 3 undergoes an iso‐space‐group P21/n‐P21/n crystalline phase transition at 257 K and a solid‐liquid transition at 410 K. These instances well demonstrate the key roles of delicate and complicated intermolecular interactions on inducing nontrivial phase transitions in hybrid crystals. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: As an extended model of conventional molecular rotors, a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here. The supramolecular self‐assembly of 18‐crown‐6 host and two rotator‐containing ion‐pair guests affords a three‐in‐one cocrystal, (2‐NH3‐iBuOH)(18‐crown‐6)[ZnBr3(H2O)], in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators. On the basis of the variable‐temperature single‐crystal X‐ray diffraction, variable‐temperature/frequency dielectric response, density functional theory calculations, and molecular dynamics simulations, it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature, and more importantly, could be controlled by a reversible polar‐to‐polar structural phase transition, i.e., from a "single‐(polar rotator)" state at low‐temperature phase to a "mixed‐dual‐(polar rotator)" state in the vicinity of transition, and to an unusual "synchronized‐dual‐(polar rotator)" state at high‐temperature phase. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: As an extended model of conventional molecular rotors, a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here. The supramolecular self‐assembly of 18‐crown‐6 host and two rotator‐containing ion‐pair guests affords a three‐in‐one cocrystal, (2‐NH3‐iBuOH)(18‐crown‐6)[ZnBr3(H2O)], in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators. On the basis of the variable‐temperature single‐crystal X‐ray diffraction, variable‐temperature/frequency dielectric response, density functional theory calculations, and molecular dynamics simulations, it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature, and more importantly, could be controlled by a reversible polar‐to‐polar structural phase transition, i.e., from a "single‐(polar rotator)" state at low‐temperature phase to a "mixed‐dual‐(polar rotator)" state in the vicinity of transition, and to an unusual "synchronized‐dual‐(polar rotator)" state at high‐temperature phase. [ABSTRACT FROM AUTHOR]

A new hybrid crystal, (Me2NH2)[CsFe(CN)5(NO)], featuring a double-layered nitroprusside-based inorganic framework with cubic-like cages encapsulating organic cations, undergoes a near-room-temperature phase transition accompanied by a dielectric switch and thermal expansion anomaly. The hidden mechanism was disclosed to be highly associated with order–disorder transition of organic cations and deformation of the inorganic framework. [ABSTRACT FROM AUTHOR]

Switching materials in channels of nonlinear optics (NLOs) are of particular interest in NLO material science. Numerous crystalline NLO switches based on structural phase transition have emerged, but most of them reveal a single‐step switch between two different second‐harmonic‐generation (SHG) states, and only very rare cases involve three or more SHG states. Herein, we report a new organic‐inorganic hybrid salt, (Me3NNH2)2[CdI4], which is an unprecedented case of a reversible three‐step NLO switch between SHG‐silent, ‐medium, ‐low, and ‐high states, with high contrasts of 25.5/4.3/9.2 in a temperature range of 213–303 K. By using the combined techniques of variable‐temperature X‐ray single‐crystal structural analyses, dielectric constants, solid‐state 13C nuclear magnetic resonance spectroscopy, and Hirshfeld surface analyses, we disclose that this four‐state switchable SHG behavior is highly associated with the stepwise‐changed molecular dynamics of the polar organic cations. This finding demonstrates well the complexity of molecular dynamics in simple hybrid salts and their potential in designing new advanced multistep switching materials. [ABSTRACT FROM AUTHOR]

Low‐concentration ethane capture is crucial for environmental protection and natural gas purification. The ideal physisorbent with strong C2H6 interaction and large C2H6 uptake at low‐concentration level has rarely been reported, due to the large pKa value and small quadrupole moment of C2H6. Herein, we demonstrate the perfectly size matching between the ultramicropore (pore size of 4.6 Å) and ethane (kinetic diameter of 4.4 Å) in a nickel pyridine‐4‐carboxylate metal–organic framework (IISERP‐MOF2), which enables the record‐breaking performance for low concentration C2H6 capture. IISERP‐MOF2 exhibits the large C2H6 adsorption enthalpy of 56.7 kJ/mol, and record‐high C2H6 uptake at low pressure of 0.01–0.1 bar and 298 K (1.8 mmol/g at 0.01 bar). Molecule simulations and C2H6‐loading crystal structure analysis revealed that the maximized interaction sites in IISERP‐MOF2 with ethane molecule originates the strong C2H6 adsorption. The dynamic breakthrough experiments for gas mixtures of C2H6/N2(1/999, v/v) and C2H6/CH4 (5/95, v/v) proved the excellent low‐concentration C2H6 capture performance. [ABSTRACT FROM AUTHOR]

Birefringent crystals, which can modulate and polarize light, play a vital role in the development of optical sensors and optoelectronic devices. Herein, we synthesized a new birefringent crystal [(C 10 N 2 H 10 )(HI 2 O 6 )(HIO 3 )(IO 3 )] with large birefringence by integrating the large π-conjugated 4,4'-bipyridine group with two types of iodates anions ([IO 3 ] - and [HI 2 O 6 ] - ) characterized by high polarizability anisotropy and strong stereochemically active lone pairs (SCALP). The crystal exhibits a large measured birefringence of 0.171 at 550 nm, surpassing most organic-inorganic hybrid iodate birefringent materials reported in the literature. Theoretical analyses reveal that the optical properties of the crystal arise primarily from the synergistic interactions between the π-conjugated 4,4'-bipyridine group and I-O groups. This research presents an effective method for the strategic integration of large π-conjugated organic cations into iodates, facilitating the design of novel birefringent materials and encouraging further exploration of superior birefringent substances.

Melt-quenched glasses of organic-inorganic hybrid crystals, i.e., hybrid glasses, have attracted increasing attention as an emerging class of hybrid materials with beneficial processability and formability in the past years. Herein, we present a new hybrid crystal, (Ph 3 PEt) 3 [Ni(NCS) 5 ] (1, Ph 3 PEt + =ethyl(triphenyl)phosphonium), crystallizing in a polar space group P1 and exhibiting thermal-induced reversible crystal-liquid-glass-crystal transitions with relatively low melting temperature of 132 °C, glass-transition temperature of 40 °C, and recrystallization on-set temperature of 78 °C, respectively. Taking advantage of such mild conditions, we fabricated an unprecedented hybrid glass-ceramic thin film, i.e., a thin glass uniformly embedding inner polar micro-crystals, which exhibits a much enhanced intrinsic second-order nonlinear optical effect, being ca. 25.6 and 3.1 times those of poly-crystalline 1 and KH 2 PO 4 , respectively, without any poling treatments., (© 2023 Wiley-VCH GmbH.)

Low-concentration ethane capture is crucial for environmental protection and natural gas purification. The ideal physisorbent with strong C 2 H 6 interaction and large C 2 H 6 uptake at low-concentration level has rarely been reported, due to the large pK a value and small quadrupole moment of C 2 H 6 . Herein, we demonstrate the perfectly size matching between the ultramicropore (pore size of 4.6 Å) and ethane (kinetic diameter of 4.4 Å) in a nickel pyridine-4-carboxylate metal-organic framework (IISERP-MOF2), which enables the record-breaking performance for low concentration C 2 H 6 capture. IISERP-MOF2 exhibits the large C 2 H 6 adsorption enthalpy of 56.7 kJ/mol, and record-high C 2 H 6 uptake at low pressure of 0.01-0.1 bar and 298 K (1.8 mmol/g at 0.01 bar). Molecule simulations and C 2 H 6 -loading crystal structure analysis revealed that the maximized interaction sites in IISERP-MOF2 with ethane molecule originates the strong C 2 H 6 adsorption. The dynamic breakthrough experiments for gas mixtures of C 2 H 6 /N 2 (1/999, v/v) and C 2 H 6 /CH 4 (5/95, v/v) proved the excellent low-concentration C 2 H 6 capture performance., (© 2021 Wiley-VCH GmbH.)

Adsorptive separation of propylene/propane (C 3 H 6 /C 3 H 8 ) mixture is desired for its potential energy saving on replacing currently deployed and energy-intensive cryogenic distillation. Realizing efficient C 3 H 6 /C 3 H 8 separation in the emerging hydrogen-bonded organic frameworks (HOFs) is very challenging owing to the lack of functional sites for preferential gas binding. By virtue of crystal engineering, we herein report a functionalized HOF (HOF-16) with free -COOH sites for the efficient separation of C 3 H 6 /C 3 H 8 mixtures. Under ambient conditions, HOF-16 shows a significant C 3 H 6 /C 3 H 8 uptake difference (by 76 %) and selectivity (5.4) in contrast to other carboxylic acid-based HOFs. Modeling studies indicate that free -COOH groups together with the suitable pore confinement facilitate the recognition and high-density packing of gas molecules. The separation performance of HOF-16 was validated by breakthrough experiments. HOF-16 is stable towards strong acidity and water., (© 2021 Wiley-VCH GmbH.)