Variable Temperature Powder X-ray Diffraction Research Articles

Host-Host Interactions Enhanced the Structural Rigidity in a 6-Fold Interpenetrated Diamondoid Metal-Organic Framework Exhibiting C2H2/C2H4 Separation.

Multi-interpenetrated metal-organic frameworks (MOFs) have exhibited excellent performance in selective adsorption due to the variable post-interspersed flexibility, but the design and control remain challenging. Herein, two anthracene-based ligands, 4,4'-(anthracene-9,10-diyl)dibenzoic acid (H2L1) and 9,10-di(pyridin-4-yl)anthracene (L2), are used to construct a new three-dimensional 6-fold interpenetrated MOF [Zn(L1)(L2)]n (NBU-X1), which exhibits multiple C-H···π interactions that enhance the structural rigidity, thereby entangling with a C2H2/C2H4 separation performance. In this material, the incorporation of abundant anthracene rings within the framework not only partitions and restricts the pore window size to a quasi-double pore but also stabilizes it through host-host interactions. The structural stability upon heating or guest displacement/removal has been investigated by single-crystal X-ray diffraction and in situ variable-temperature powder X-ray diffraction, in contrast to the extreme flexibility of most multi-interpenetrated MOFs. The performance of purifying C2H4 from C2H2/C2H4 mixtures has been proved by dynamic breakthrough tests.

Thermoanalytical techniques applied to the solid-state characterization of atorvastatin calcium trihydrate form I

Atorvastatin calcium trihydrate (ACT) is a synthetic lipid-lowering agent whose thermal character remains largely unknown or else mischaracterized due to being called both “atorvastatin” and “atorvastatin form I” indiscriminately in the literature. Developing stable drugs, however, requires ensuring and thus understanding the reliable thermal behavior of trihydrate drugs, for pharmaceutical manufacturing can involve temperatures that might cause phase transition and/or the dehydration of the drugs, with implications for its physical characteristics, its chemical characteristics, and/or the pharmaceutical product's bioactivity. Against that background, in our study we investigated both a solid-state and thermal characterization of ACT via powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot-stage microscopy (HSM), and ex situ variable temperature PXRD techniques, all as integral parts of drug development. DSC and TGA curves clarified ACT's thermal stability and dehydration, and the ACT sample was identified as Form I of the trihydrate, which remains stable until approximately 40 °C. DSC showed no significant changes during melting with different heating rates, while the TGA curve revealed the stepwise loss of water molecules following heating. Ex situ PXRD suggested no abrupt changes to the trihydrate's crystal lattice during the dehydration of the first two moles of water molecules. Moreover, HSM clearly showed a unique water loss event never before visualized. Last, HSM confirmed the drug's crystallinity, its crystal shape, and the presence of an isotropic liquid after continuous heating, which remained until cooling to room temperature.

Combining a Drug and a Nutraceutical: A New Cocrystal of Praziquantel and Curcumin

This study explores the co-crystallization between the drug praziquantel (PZQ) and the nutraceutical curcumin (CU). The investigation revealed two novel solid forms: a cocrystal solvate with ethyl acetate and a non-solvated cocrystal. This novel drug–nutraceutical cocrystal is a praziquantel–curcumin (2:1) cocrystal. The cocrystal solvate has ethyl acetate molecules occupying the voids with minimal interactions within the crystal lattice. The application of heat treatment induces solvent removal and prompts the transition to the non-solvated cocrystal, as highlighted by variable-temperature X-ray powder diffraction (VT-XRPD). Thermal analyses demonstrate the stability of the cocrystal solvate up to approximately 100 °C, beyond which it transforms into the non-solvated phase, which eventually melts at 130 °C.

Systematic study of ionic conduction in silver iodide/mesoporous alumina composites 2: effects of silver bromide doping.

In our preceding paper (Y. Fukui et al., Phys. Chem. Chem. Phys., 2023, 25, 25594-25602), we reported a systematic study of the Ag+-ion conducting behaviour of silver iodide (AgI)-loaded mesoporous aluminas (MPAs) with different pore diameters and AgI-loading ratios. By optimising the control parameters, the Ag+-ion conductivity has reached 7.2 × 10-4 S cm-1 at room temperature, which is more than three orders of magnitude higher than that of bulk AgI. In the present study, the effect of silver bromide (AgBr)-doping in the AgI/MPA composites on Ag+-ion conductivity is systematically investigated for the first time, using variable-temperature powder X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy measurements. The AgBr-doped AgI/MPA composites, AgI-AgBr/MPA, formed a homogeneous β/γ-AgI-structured solid solution (β/γ-AgIss) for the composites with AgBr ≤ 10 mol%, above which the composites underwent a phase separation into β/γ-AgIss and face-centred cubic AgBr solid solutions (AgBrss). The onset temperature of the exothermic peaks attributed to the transition from α-AgI-structured solid-solution phase to β/γ-AgIss or AgBrss decreased with increasing the AgBr-doping ratio. The room-temperature ionic conductivity of the AgI-AgBr/MPA composites exhibited a volcano-type dependence on the AgBr-doping ratio with the highest value (1.6 × 10-3 S cm-1) when the AgBr content was 10 mol%. This value is more than twice as high as that of the highest conducting AgI/MPA found in our previous study.

Highly Selective p-Xylene Separation from Mixtures of C8 Aromatics by a Nonporous Molecular Apohost.

High and increasing production of separation of C8 aromatic isomers demands the development of purification methods that are efficient, scalable, and inexpensive, especially for p-xylene, PX, the largest volume C8 commodity. Herein, we report that 4-(1H-1,2,4-triazol-1-yl)-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (TPBD), a molecular compound that can be prepared and scaled up via solid-state synthesis, exhibits exceptional PX selectivity over each of the other C8 isomers, o-xylene (OX), m-xylene (MX), and ethylbenzene (EB). The apohost or α form of TPBD was found to exhibit conformational polymorphism in the solid state enabled by rotation of its triazole and benzene rings. TPBD-αI and TPBD-αII are nonporous polymorphs that transformed to the same PX inclusion compound, TPBD-PX, upon contact with liquid PX. TPBD enabled highly selective capture of PX, as established by competitive slurry experiments involving various molar ratios in binary, ternary, and quaternary mixtures of C8 aromatics. Binary selectivity values for PX as determined by 1H NMR spectroscopy and gas chromatography ranged from 22.4 to 108.4, setting new benchmarks for both PX/MX (70.3) and PX/EB (59.9) selectivity as well as close to benchmark selectivity for PX/OX (108.4). To our knowledge, TPBD is the first material of any class to exhibit such high across-the-board PX selectivity from quaternary mixtures of C8 aromatics under ambient conditions. Crystallographic and computational studies provide structural insight into the PX binding site in TPBD-PX, whereas thermal stability and capture kinetics were determined by variable-temperature powder X-ray diffraction and slurry tests, respectively. That TPBD offers benchmark PX selectivity and facile recyclability makes it a prototypal molecular compound for PX purification or capture under ambient conditions.

Stable and rapid thermochromic reversibility in acene alkylamine intercalated layered hybrid perovskites

Since the discovery of thermochromism in halide perovskites, new perovskite materials with excellent thermochromic properties have been developed. Among them, two-dimensional (2D) layered hybrid perovskites have been extensively explored because of their highly tunable structures and unique thermochromic responses. In this study, the thermochromism in acene alkylamine-spaced 2D perovskite single crystals (PEA)2PbI4 and (NEA)2PbI4 (PEA = 2-phenylethylammonium, NEA = 2-(2-naphthyl)-ethanammonium) is studied. These 2D perovskites undergo a distinct color change between orange and red during heating and cooling cycles, with the corresponding optical bandgap modulation monitored by variable-temperature absorption spectroscopy. The thermochromism in (PEA)2PbI4 and (NEA)2PbI4 is caused by lattice expansion, as confirmed by thermogravimetric–differential scanning calorimetry and variable-temperature powder X-ray diffraction. Compared with the thermochromism caused by structural phase transition, lattice-expansion-modulated thermochromism demonstrates rapid color change and luminescence recovery, and enhanced thermal cycling stability. This study presents a new strategy for developing thermochromic halide perovskites for multifunctional applications.

Structure and dielectric properties in Mg/Nb co-substituted bismuth sodium titanate

A systematic study of pseudo-isovalent B site co-substitution of Ti4+ by Mg2+ and Nb5+ in bismuth sodium titanate is presented. A complete solid solution in the Bi0.5Na0.5Ti1−x(Mg1/3Nb2/3)xO3 system is formed. With increasing level of substitution, dielectric anomalies associated with depoling and maximum permittivity temperatures (Td and Tm, respectively) are suppressed and shift to lower temperatures. Variable temperature X-ray powder diffraction on the x = 0.2 composition reveals a non-linear thermal expansion at temperatures below Tm. B-site co-substitution by Mg and Nb has the effect of interrupting the long-range ferroelectric ordering in the system, resulting in lower saturation and remnant polarizations. A maximum energy storage density of 4.14 J cm−3 with a recoverable energy density of 2.35 J cm−3 was obtained for the x = 0.1 composition, while the x = 0.5 composition appears to have the best balance between energy storage and energy efficiency.

A novel contribution to the M3B6O10X hexaborate family: The new silver compound Ag3B6O10Br and thermal behavior of Ag3B6O10(NO3) and Na3B6O10I

In this work, we present a new borate, Ag3B6O10Br, as well as thermal properties of two recently reported members of M3B6O10X family, Ag3B6O10(NO3) and Na3B6O10I. The structure of Ag3B6O10Br is non-centrosymmetric, Pnm21, and exhibits a new version of packing the ionic Ag–Br and covalent B–O frameworks. The non-centrosymmetry is induced by alternation of disordered and ordered borate “layers” normal to a. The Ag–Br sublattice is also strongly disordered and exhibits pronounced ahnarmonicity of thermal vibrations modeled using the Gram – Charlier series. Thermal behavior of Ag3B6O10Br, Ag3B6O10(NO3) and Na3B6O10I was characterized using variable-temperature powder X-ray diffraction and thermal analysis. The thermal behavior of Ag3B6O10Br (αa = −0.5, αb = −7.4, αc = 41.5 at 200°С), Ag3B6O10(NO3) (αa = 4.5, αb = 4.8, αc = 31.8 at 200°С), and Na3B6O10I (αa = 9.4, αb = −1.2, αc = 48.3 at 200°С) is strongly anisotropic due to the alignment of the hexaborate B6O13 groups in the structure.

Hydrogen-bonded nickel(II)-organosulfonate framework: Thermal expansion behavior, proton conduction, and magnetic properties

Metalo Hydrogen-bonded organic frameworks are emerging supramolecular platforms for designing functional molecular materials. Herein, we reported the supramolecular structure, thermal, magnetic, and proton conduction properties of a hydrogen-bonded nickel(II)-organosulfonate framework, [Ni(H2O)6][NPS]2 (NiHOF, HNPS = naphthalene-2-sulphonic acid). Single-crystal X-ray diffraction studies reveal a two-dimensional hydrogen-bonded network sustained by multiple and charge-assisted OH···O H bonds between hexaaquanickel(II) cations and organosulfonate anions. Additionally, continuous ca. 0.47 × 0.70 nm2 windows were formed within the framework. The thermal stability of the NiHOF was confirmed by thermal gravimetric analysis and variable temperature single-crystal and powder X-ray diffraction patterns. N2 sorption isotherms suggest an ultramicroporous supramolecular framework of NiHOF with permanent porosity. The anisotropic positive thermal expansion behavior of NiHOF was evidenced by the dynamic crystallography experiments. Magnetic measurements indicate easy-axis magnetic anisotropy (D = -10.5 cm−1) of the NiHOF while no slow magnetic relaxation behavior. Electrochemical impedance spectroscopy indicates the temperature and humidity dependence of conductivities of NiHOF. At 50 °C and 70% relative humidity, the conductivity is 1.13 × 10−4 S·cm−1, revealing a supramolecular proton conductor of NiHOF. This work provides a potential way for designing novel thermal, magnetic, and electrical molecular materials through the supramolecular assembly of inorganic and organosulfonate synthons.

Thermodynamic and Kinetic Mechanism of the Phase Transition from Aztreonam Dihydrate to Anhydrates

In this work, two anhydrates (form A and form B) and one dihydrate (form C) of aztreonam were found and were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared spectroscopy. Dynamic vapor adsorption and variable-temperature PXRD experiments were carried out to study their thermal stability and moisture absorption stability. Furthermore, the critical water activity of aztreonam at 10–45 °C was determined, and it was found that the water activity determines the dehydration process of form C. The solubility of form A and form B in methanol solvent was measured at 10–45 °C to decide the thermodynamic stability of the polymorphs, and it was found that form B is thermodynamically stable below 28 °C, while form A is thermodynamically stable above 28 °C. The competitive suspension experiments further proved that form A and form B are enantiotropic polymorphs. In addition, the solution-mediated phase transition (SMPT) process of aztreonam form C was in situ monitored using Raman spectroscopy. The results show that the SMPT process is jointly controlled by the dissolution of the dihydrate and the nucleation of anhydrates, in which temperature plays a very important role. Finally, the SMPT mechanism of the dihydrate form is proposed.

Metalo Hydrogen-Bonded Organic Frameworks Self-Assembled by Charge-Assisted Synthons for Ultrahigh Proton Conduction

Hydrogen-bonded organic frameworks (HOFs) have been well recognized for constructing solid-state proton-conducting materials due to their inherent well-defined H-bonded networks; however, the design and synthesis of stable HOFs showing ultrahigh superprotonic conductivity is still challenging. Herein, we reported a facile and effective synthetic strategy to build high proton-conducting metalo hydrogen-bonded organic–inorganic frameworks (MHOFs) through charge-assisted inorganic and organic synthons. The supramolecular self-assembly of simple metal salts and tetra-carboxylic acids gives rise to two hydrogen-bonded frameworks, [M(H2O)6][H2tcba] (M = Zn2+, Ni2+; H4tcba = 1,2,4,5-benzenetetracarboxylic acid). X-ray crystallography and gas adsorption confirmed the nonporous nature of the HOIFs. Variable-temperature single-crystal and powder X-ray diffraction experiments reveal the thermal and water stability of the supramolecular structures sustained by exclusively charge-assisted hydrogen bonds. The high density of carboxylic acid groups and coordinated water molecules provide ample protons and hydrophilic environments for efficient proton transport; therefore, variable-temperature and -humidity electrochemical impedance spectroscopy revealed that MHOFs are good supramolecular proton conductors with conductivities up to 1.1 × 10–2 and 2.1 × 10–2 S·cm–1 for 1 and 2, respectively, at 80 °C under 97% RH. Our study demonstrates great potential of charge-assisted inorganic and organic synthons in the design and construction of proton-conducting HOIFs.

Highly Productive C3H4/C3H6 Trace Separation by a Packing Polymorph of a Layered Hybrid Ultramicroporous Material.

Ultramicroporous materials can be highly effective at trace gas separations when they offer a high density of selective binding sites. Herein, we report that sql-NbOFFIVE-bpe-Cu, a new variant of a previously reported ultramicroporous square lattice, sql, topology material, sql-SIFSIX-bpe-Zn, can exist in two polymorphs. These polymorphs, sql-NbOFFIVE-bpe-Cu-AA (AA) and sql-NbOFFIVE-bpe-Cu-AB (AB), exhibit AAAA and ABAB packing of the sql layers, respectively. Whereas NbOFFIVE-bpe-Cu-AA (AA) is isostructural with sql-SIFSIX-bpe-Zn, each exhibiting intrinsic 1D channels, sql-NbOFFIVE-bpe-Cu-AB (AB) has two types of channels, the intrinsic channels and extrinsic channels between the sql networks. Gas and temperature induced transformations of the two polymorphs of sql-NbOFFIVE-bpe-Cu were investigated by pure gas sorption, single-crystal X-ray diffraction (SCXRD), variable temperature powder X-ray diffraction (VT-PXRD), and synchrotron PXRD. We observed that the extrinsic pore structure of AB resulted in properties with potential for selective C3H4/C3H6 separation. Subsequent dynamic gas breakthrough measurements revealed exceptional experimental C3H4/C3H6 selectivity (270) and a new benchmark for productivity (118 mmol g-1) of polymer grade C3H6 (purity >99.99%) from a 1:99 C3H4/C3H6 mixture. Structural analysis, gas sorption studies, and gas adsorption kinetics enabled us to determine that a binding "sweet spot" for C3H4 in the extrinsic pores is behind the benchmark separation performance. Density-functional theory (DFT) calculations and Canonical Monte Carlo (CMC) simulations provided further insight into the binding sites of C3H4 and C3H6 molecules within these two hybrid ultramicroporous materials, HUMs. These results highlight, to our knowledge for the first time, how pore engineering through the study of packing polymorphism in layered materials can dramatically change the separation performance of a physisorbent.

Large Degree of Variation in Sorption Properties within a System of Isoreticular, Mixed-Ligand Ni- and Co-Based 2-Periodic Metal–Organic Frameworks

Two Ni-based and two Co-based mixed-ligand metal–organic frameworks (MOFs), which are all isoreticular with each other, are shown to have a large variation in nitrogen, carbon dioxide, hydrogen, and water vapor sorption properties, despite their similar structures. The MOFs have 1,2-bis(4-pyridyl)ethane (bpe) as the common ligand with the second ligand being either 2-nitroterephthalate (2-nta) or 2-bromoterephthalate (2-bta) for the Ni-based MOFs or 2-nta or 2-aminoterephthalate (2-ata) for the Co-based MOFs. The four MOFs have the formula [Ni(2-nta)(bpe)(H2O)2]n·2(DMA)n (1), [Ni(2-bta)(bpe)(H2O)2]n·2.8(DMF)n (2), [Co(2-nta)(bpe)(H2O)2]n·2(DMA)n (3), and [Co(2-ata)(bpe)(H2O)2]n·3(DMA)n·(H2O)n (4), respectively, where DMA = N,N′-dimethylacetamide and DMF = N,N′-dimethylformamide. Variable-temperature powder X-ray diffraction (VT-PXRD) studies indicate that the activated MOF structures are different from those of the as-synthesized MOFs, showing that the 2-periodic layers are dynamic upon desolvation. For the same metal ion, the MOF involving the 2-nta ligand has higher sorption, while sorption for the Ni-based MOFs is higher than for the Co-based MOFs. MOF 1 has the highest sorption within the isoreticular series and also has the highest sorption (the highest for water vapor) compared to other MOFs with the same or related ligands.

Unusual In Situ Transformation of Metastable Co-Crystal Forms into a Stable Form, in Solution and Solid State, and the [2 + 2] Photochemical Reactivity in the Crystalline Forms

Isolation of multiple composition co-crystals from a one-pot crystallization flask and in situ transformations of the crystals are not common phenomena. We describe, herein, thoroughly characterized three unusual co-crystals of citric acid (CA) and 1,2-bis(4-pyridyl)ethene (bpyee) with different molecular compositions (1:1, α; 2:2, β; and 2:3, γ) that were obtained from a one-pot crystallization flask of a CH3OH solution with equimolar co-formers. The three co-crystals can be distinguished by their morphology and appearance at various stages of the crystallization process. In the first instance, needle-shaped (β) crystals are formed on the edge of the flask, followed by plates (γ) in the bulk of the solution, and finally, the entire flask with only rod-shaped crystals (α), indicating the in situ conversion of β- and γ-forms into α-form. Interestingly, in the solid state, isolated crystals are observed to undergo conversion, but in a different way than solution growth, as characterized by in situ variable-temperature powder X-ray diffraction, with β- and α-forms converting into γ-form. Furthermore, all of the forms undergo [2 + 2] photochemical reactivity upon UV irradiation due to the favorable Schmidt’s photoreactive distance between the adjacent bpyee molecules in α- and γ-forms, with the former following a single-crystal-to-single-crystal transformation process also, while β-form, despite having bpyee molecules separated by 7.68 Å, through conversion into γ-form.

Exploring the thermal behaviour of the solvated structures of nifedipine.

Understanding the solvation and desolvation of pharmaceutical materials is an important part of materials discovery and development. In situ structural data are vital to understand the changes to crystal form that may occur in the system. In this study, the isolation and characterization of seven solvates of the L-type calcium channel antagonist, nifedipine, is described using variable-temperature powder X-ray diffraction so that the structural evolution as a function of temperature can be followed. The solvates reported herein can be split into those that are structurally similar to the previously reported dimethyl sulfoxide (DMSO) and dioxane solvates and those that have a novel packing arrangement. Of particular note is the solvate with tetrahydrofuran (THF) which has a hydrogen-bonding motif between the nifedipine molecules very similar to that of metastable β-nifedipine. In addition to variable-temperature X-ray diffraction, the stability of the solid forms was assessed using differential scanning calorimetry and thermogravimetric analysis and indicates that in all cases desolvation results in the thermodynamically stable α-polymorph of nifedipine even with the THF solvate. From the diffraction data the pathway of desolvation during heating of the DMF solvate showed conversion to another likely 1:1 polymorph before desolvation to α-nifedipine. The desolvation of this material indicated a two-stage process; first the initial loss of 90% of the solvent before the last 10% is lost on melting. The methanol solvate shows interesting negative thermal expansion on heating, which is rarely reported in organic materials, but this behaviour can be linked back to the winerack-type hydrogen-bonding pattern of the nifedipine molecules.

Thermally Crosslinked Hydrogen-Bonded Organic Framework Membranes for Highly Selective Ion Separation.

The weak bonding energy and flexibility of hydrogen bonds can hinder the long-term use of hydrogen-bonded organic framework (HOF) materials under harsh conditions. Here we invented a thermal-crosslinking method to form polymer materials based on a diamino triazine (DAT) HOF (FDU-HOF-1), containing high-density hydrogen bonding of N-H⋯N. With the increase of temperature to 648 K, the formation of -NH- bonds between neighboring HOF tectons by releasing NH3 was observed based on the disappearance of the characteristic peaks of amino groups on FDU-HOF-1 in the Fourier transform infrared (FTIR) and solid-state nuclear magnetic resonance (ss-NMR). The variable temperature PXRD indicated the formation of a new peak at 13.2° in addition to the preservation of the original diffraction peaks of FDU-HOF-1. The water adsorption, acid-base stability (12 M HCl to 20 M NaOH) and solubility experiments concluded that the thermally crosslinked HOFs (TC-HOFs) are highly stable. The membranes fabricated by TC-HOF demonstrate the permeation rate of K+ ions as high as 270 mmol m-2 h-1 as well as high selectivity of K+/Mg2+ (50) and Na+/Mg2+ (40), which was comparable to Nafion membranes. This study provides guidance for the future design of highly stable crystalline polymer materials based on HOFs.

Comparison of the physical properties of disodium etidronate amorphous forms prepared by different manufacturing methods

Amorphous forms of disodium etidronate were prepared by three manufacturing methods, heat drying, freeze drying, and anti-solvent precipitation, and the effects of these methods on the physical properties of disodium etidronate amorphous forms were evaluated for the first time. Variable temperature X-ray powder diffraction and thermal analyses revealed that these amorphous forms had different physical properties such as glass transition point, water desorption, and crystallization temperatures. These differences can be explained by the molecular mobility and water content in amorphous forms. The differences in the structural characteristics related to the differences in these physical properties could not be detected clearly by the spectroscopic methods like Raman spectroscopy and X-ray absorption near-edge spectroscopy. Dynamic vapor sorption analyses demonstrated that all amorphous forms were hydrated to form I, a tetrahydrated form, at above 50% relative humidity, and the transition to form I was irreversible. These amorphous forms require strict humidity control to avoid crystallization. Among the three amorphous forms of disodium etidronate, the amorphous form prepared by heat drying was the most suitable for manufacturing the solid formulation, considering the low water content and low molecular mobility.

Elastic Properties of the Iron(II)–Triazole Spin Crossover Complexes [Fe(Htrz)2trz]BF4 and [Fe(NH2trz)3]SO4

Two benchmark Fe(II)-triazole spin-crossover (SCO) compounds, [Fe(Htrz)2trz]BF4 (1) and [Fe(NH2trz)3]SO4 (2), have been investigated using variable temperature and pressure powder X-ray diffraction, dynamical mechanical analysis, and differential scanning calorimetry techniques. We assessed the transformation strain, the compressibility, and their anisotropy in both compounds. The measured bulk moduli are relatively high (20 and 13 GPa in 1 and 2, respectively), but against expectations, the Fe–triazole chain direction is the most compressible crystal axis in 1. We revealed considerable elastic softening and associated mechanical damping at the SCO in both compounds, which we interpreted, using the Landau theory, as a consequence of the coupling between the spin state and the lattice strain. The magnitudes of the elastic potential energy (∼15%), stored elastic work (<2–3%), and frictional work (<3–4%) with respect to the latent heat of the spin transition (26.8 and 19.5 kJ/mol in 1 and 2, respectively) have been also assessed. The knowledge of these properties is important both for a better understanding of the SCO behavior of this important family of complexes and for guiding their integration into mechanical transducers and other technological applications.

Synthesis and Crystal Structure of a New RTH-Type Precursor and Its Interlayer Expanded Zeolite.

Two dimensional zeolites have drawn a lot of attention due to their structural diversity and chemical composition, which can be used to obtain 3D zeolites, for which there is no direct synthesis. Here, a new layer silicate zeolite L was synthesized using the N, N-dimethyl-(2-methyl)-benzimidazolium as the organic structure-directing agent (OSDA) in the presence of fluoride. Structure determination by single-crystal X-ray diffraction reveals that the pure silica precursor with five-ring pores in the crystalline sheets is composed of the rth layer stacking along the (001) direction in an …AAAA… sequence with SDA+ cations and F- residing within the interlayer spaces. Variable temperature powder X-ray diffraction (PXRD) results showed that the new layer could transform into a 3D RTH topology structure at 350 °C via 2D-3D topotactic transformation. Furthermore, a new 3D zeolite material is obtained by treating the original layer with a diethoxydimethylsilane agent under hydrochloric acid condition (HCl-DEDMS). Based on the PXRD results and the original layer structure, the new 3D zeolite structure expanding the rth layer with another Si atom is constructed, which possesses a 10×8×6 channel system. It displays a high BET surface area of 188 cm3 /g with an external surface area of 130 cm3 /g. The structure and textural properties pave a way for potential catalytic applications. The research not only provides a new layered zeolite, broadening the 2D zeolite framework types, but also allows for the discovery of a new stable 3D zeolite expanding the RTH structure with Si atom, which hasn't been reported yet.

Second Harmonic Generation in the Polar A′SmNb2O7 (A′ = Rb, Cs) Dion–Jacobson Layered Perovskites

Members belonging to the Dion–Jacobson (DJ) family of layered perovskites have time and again proven to be the preferred materials of choice for the exploration and identification of polar structures. We report two noncentrosymmetric n = 2 DJ members, A′SmNb2O7 (A′ = Rb, Cs), prepared by high-temperature solid-state reactions, thus expanding the polar n = 2, DJ series as A′ANb2O7 (A′ = Rb, Cs; A = La, Pr, Nd, Sm, Bi). Optical second harmonic generation measurements utilizing 1064 nm substantiated the existence of Type I phase matchable compounds, and the efficiencies were 4 to 6 times higher than the standard KDP. Structural refinements by the Rietveld method confirm the polar orthorhombic space groups of I2cm and P21am, respectively, for RbSmNb2O7 [a = 5.4368(3) Å, b = 5.3944(3) Å, c = 21.9051(1) Å] and CsSmNb2O7 [a = 5.4669(5) Å, b = 5.4158(4) Å, c = 11.1437(1) Å]. The orthorhombic distortions and symmetry lowering were further supported by the Raman spectroscopy measurements. The difference in the orthorhombic a and b parameters (∼0.05 Å) possibly originates from the chemical pressure induced by the smaller ionic size of Sm3+ (1.24 Å, XII) as compared to other Ln3+ (La, Pr, Nd) ions. Ferroelectric switching of A′SmNb2O7 (A′ = Rb, Cs) oxides is demonstrated by the polarization hysteresis loops observed at room temperature with remanent polarization values of 5.3 and 2.0 μC/cm2 corresponding to the Rb and Cs analogues. Variable-temperature powder X-ray diffraction measurements confirmed the phase transition from polar to anti-polar transitions around temperatures ∼1273 and ∼1173 K, respectively, for the Rb and Cs analogues. Structural analysis results in the identification of prototype tetragonal (a ∼ 3.88 Å, c ∼ 11.20 Å) centrosymmetric structures relating the transition temperatures to potential Curie temperatures. The transitions coincide with the observed Curie point of 1113 K for CsSmNb2O7, from the temperature-dependent relative permittivity measurements, and a much higher temperature is expected for the Rb analogue.