Ionic Crystal Structure Research Articles

Evaluation of B-Site Doped Barium Niobate Perovskite Anodes for the Electrochemical Oxidative Coupling of Methane

More efficient usage of shale gas reserves and natural gas resources will allow for higher olefin yields and lower greenhouse gas emissions. The oxidative coupling of methane (OCM) is a direct pathway for converting methane to ethylene at temperatures >700 °C. OCM catalysts preferably avoid COx products and limit coke formation on the catalyst. Often, catalysts are analyzed via computationally expensive DFT computations in combination with experimental results leading to long lead times for catalyst development. Perovskite oxide catalysts are useful for OCM due to their flexible bond networks and varied properties (conductivity, selectivity, surface area) based on synthesis/doping. This work aims to illustrate the utility of the bond-valence bond-length model (ionic model)1 ,2 in conjunction with gas reduction experiments for rapid structure evaluation of the co-doped perovskite BaMg0.33Nb0.67-xFexO3-δ (BMNF, x=0.17,0.25,0.33). This perovskite catalyst has previously been adopted as a CO2 sensing material3 and an active/stable anode for the electrochemical oxidative coupling of methane4 (E-OCM). Further evaluation of this perovskite by our group illustrated the unique stability of ionic Fe into the BMNF while performing the oxidative coupling of methane5. This work delves into the crystal structure of the BMNF material as well as its chemical stability validated using a much more facile computational methodology featuring the bond-valence bond-length method. XPS, XRD, and reduction/oxidation high temperature cycling are utilized in conjunction to illustrate the stabilizing mechanisms for cations within the BMNF perovskite when exposed to highly reducing environments. References (1) Pauling, L. "The principles determining the structure of complex ionic crystals."J. Am. Chem. Soc. 1929, 51 1010-1026.(2) Lufaso, M. W.; Woodward, P. M. Prediction of the Crystal Structures of Perovskites Using the Software Program SPuDS. Acta Crystallogr. B 2001, 57 (6), 725–738. https://doi.org/10.1107/S0108768101015282.(3) Kannan, R.; Mulmi, S.; Thangadurai, V. Synthesis and Characterization of Perovskite-Type BaMg0.33Nb0.67−xFexO3−δ for Potential High Temperature CO2 Sensors Application. J. Mater. Chem. A 2013, 1 (23), 6874–6879. https://doi.org/10.1039/C3TA10572E.(4) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Ramaiyan, K. P. Highly Stable Doped Barium Niobate Based Electrocatalysts for Effective Electrochemical Coupling of Methane to Ethylene. Adv. Mater. Interfaces 2022, 9 (27), 2200796. https://doi.org/10.1002/admi.202200796.(5) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Electrochemical oxidative coupling of methane: deciphering the exceptional properties of BaMg0.33Nb0.67-xFexO3-δ for enhanced electrocatalysis and durable operation. Accepted by Energy & Fuels Feb. 2024

Fabrication of (K,Rb)2CuCl3 and (K,Rb)2CuBr3 Single Crystal Scintillators with Efficient Luminescence

Scintillators are phosphor materials that emit many low-energy photons upon exposure of high-energy ionizing radiation such as X- and γ-rays. They have been utilized in combination with photodetectors for radiation measurements, including medical imaging [1], underground resources exploration [2], luggage inspection [3], and structural analysis of materials [4]. The required characteristics of scintillators are different depending on the applications. For example, high light yield (LY) for high energy resolution and high signal-noise ratio, short decay time for high time resolution, large effective atomic number for high interaction probability with ionizing radiation, and low hygroscopicity for long-term usability are important. Halide crystals such as Tl-doped CsI and NaI have been utilized as practical scintillators because of their high LY owing to the medium bandgap energy (5.8–6.3 eV) [4, 5]. However, most halide crystals have issues related to chemical instability due to hygroscopicity. Thus, novel non-hygroscopic scintillators with high LY have been desired. Nowadays, Cu-based halide scintillators have received attention owing to good properties such as high photoluminescence quantum yield (PLQY), scintillation LY, and no hygroscopicity. We have focused on the alkali copper halide group such as A 2CuX 3 (A = K, Rb X = Cl, Br). They showed high PLQY (~100%) attributed to the recombination of self-trapped excitons under UV and X-ray irradiations [6, 7]. However, their scintillation LYs under γ-rays have not been clarified. According to Hume-Rothery rules [8], a continuous solid solution containing two or more components can be easily formed when two substances with similar ionic radius and crystal structure are partially mixed in the matrix. In continuous solid solutions, emission properties of phosphors were improved by optimizing energy levels in the bandgap and lattice defects involved in the luminescence [9]. On the basis of the rules, the continuous solid solutions of (K,Rb)2CuCl3 and (K,Rb)2CuBr3 can be grown. Thus, we fabricated (K,Rb)2CuCl3 and (K,Rb)2CuBr3 to enhance the scintillation properties. In this presentation, the scintillation properties such as the X-ray-induced scintillation spectra, the scintillation decay curves, afterglow curves, and pulse-height spectra of 1 37Cs γ-rays (662 keV) measurements will be presented.[1] C.W. Eijk., Phys. Med. Biol., 47 (2002) R85. [2] A. Nikitin et.al., IEEE Nucl. Sci. Symp. Med. Imag. Conf. (2010) 1214. [3] V.D. Ryzhikov et.al., IEEE Symposium Conference Record Nuclear Science (2004) 4291. [4] V.V. Nagarkar et.al., IEEE Trans. Nucl. Sci. 45 (1998) 492. [5] M. Moszynski et.al., Nucl. Instrum. Methods Phys. Res. A (2004) 4291. [6] T.D Creason et.al., Chem. Mater. 32 (2020).

Application of novel Dy0.06Gd0.02Er0.02Bi1.9O3 oxide ion electrolyte for intermediate-temperature reversible solid oxide cells

Bismuth-based oxides are promising electrolyte materials for Reversible Solid Oxide Cells (RSOCs) due to their high ion conductivity and rapid surface oxygen exchange kinetics. In this work we propose a multi-element doping strategy to obtain a novel Dy0.06Gd0.02Er0.02Bi1.9O3 (DGESB) quaternary oxide bismuth material whose ionic conductivities and crystal structure are characterized by AC impedance and X-ray diffraction technique in the temperature range from 600 to 700 °C. Along with promising structure stability and durability, our novel DGESB showed a remarkable ionic conductivity that is 65 times higher than the commercial yttria-stabilized zirconia (YSZ) electrolyte at 700 °C. With composite electrode of DGESB + LCN (LaCo0.6Ni0.4O3) and DGESB/YSZ bilayer electrolyte consisting of RSOC symmetric cell, which achieves a high peak power density (PPD) of 1.62 W/cm2 in fuel cell mode which is 2.7 times higher than that of YSZ single-layer electrolyte, while the electrolysis current density is as high as 1.66 A/cm2 at 1.3 V under H2/H2O:50/50 in electrolysis mode at the same operation temperature of 700 °C. The electrochemical performance measurements revealed a certain stable operation for 200 h in fuel cell mode. The performance degradation can be attributed to the microstructure evolution at the interface between electrolyte and electrodes. The high ionic conductive DGESB proves to be an excellent intermediate electrolyte layer for improving cell performance in RSOCs.

Solvent-Free in Situ Synthesis of a CsPbBr3 Nanocrystal/ZrO2 Hybrid Phosphor with Excellent Thermal Stability for White Light-Emitting Diodes.

All-inorganic cesium lead halide perovskite CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are emerging as promising candidates in light-emitting diodes (LEDs) owing to their excellent luminescent properties. However, CsPbX3 NCs are extremely susceptible to the elevated temperature associated with prolonged LED operation due to their low formation energy and soft ionic crystal structure. Here, CsPbBr3 NCs hybridized with ZrO2 were in situ synthesized by a rapid solvent-free method under an ambient environment for the first time, which was also suitable for large-scale production. The as-prepared CsPbBr3/ZrO2 hybrid phosphor not only presented enhanced photoluminescence (PL) properties but also exhibited improved thermal stability. For example, the PL intensity of the CsPbBr3/ZrO2 hybrid phosphor could retain 70% of the initial value at 130 °C, obviously higher than that of 34% for pure CsPbBr3. The exceptional thermal stability of the CsPbBr3/ZrO2 hybrid phosphor could be attributed to the introduction of ZrO2, which effectively preserved the initial perovskite structure of CsPbBr3 during heat treatment, as confirmed by XRD results. The as-prepared CsPbBr3/ZrO2 hybrid phosphor had great practical applications verified by the construction of white LEDs (WLEDs) with a luminance degradation of only 9% after continuous operation for 24 h at the initial luminance of 2000 cd m-2, which was significantly better than that of 63% for control WLEDs. The proposed thermally stable hybrid phosphor is expected to greatly contribute to the industrialization process of perovskites.

Stability of inorganic ionic structures: the uniformity approach.

The crystal structure uniformity is numerically estimated as the standard deviation of the crystal space quantizer 〈G3〉. This criterion has been applied to explore the uniformity of ionic sublattices in 21465 crystal structures of inorganic ionic compounds. In most cases, at least one kind of sublattice (whole ionic lattice, cationic or anionic sublattice) was found to be highly uniform with a small 〈G3〉 value. Non-uniform structures appeared to be either erroneous or essentially non-ionic. As a result, a set of uniformity criteria is proposed for the estimation of the stability of ionic crystal structures.

Dissolution process and mechanism of montmorillonite in oxalic acid and sulfuric acid media at various pH levels

The dissolution of silicate minerals plays a crucial role in many natural geological processes. In order to better comprehend the reaction mechanisms and dissolution characteristics of montmorillonite in different acidic systems, the effects of interfacial reactions of montmorillonite with oxalic and sulfuric acid solutions at various pH levels on the ionic dissolution, crystal structure, and micro-morphology were studied, and the morphology of aluminum and saturation index of secondary mineral were simulated. It was shown that the dissolution amounts of Mg2+, Al3+ and Si4+ in montmorillonite structure decreased with the increase of pH value, which reflected the dependence of montmorillonite dissolution on the pH value of solution. The dissolution percentages of Mg2+, Al3+ and Si4+ after the reaction of montmorillonite with oxalic acid solution were greater than those in sulfuric acid solution, and the highest dissolution rate of Al3+, indicated that both ligands and protons attacked the surface sites of montmorillonite and accelerated the dissolution of ions. Moreover, oxalate ligands exerted specific binding effects on Al3+ ions. While reacting with oxalate and sulfate, the tetrahedral, octahedral and interlayer cations of montmorillonite exhibited the non-stoichiometric and inconsistent dissolution. The oxalate ligands have a strong complexation effect on Al3+, so that Al3+ in oxalate solution exists in the form of aluminum oxalate complex, which reduces the effective concentration of Al3+ in solution and promotes the dissolution of Al3+ in montmorillonite structure. The Mg2+ ions settled at octahedral substitution sites possessed weak stability, while those from the interlayer featured strong interlayer interchangeability, demonstrating the dissolution percentage up to 10.85 % and 8.62 % even in oxalic and sulfuric acid solutions at pH of 6.5. All secondary mineral phases in the solution were undersaturated, making the montmorillonite dissolution difficult to balance. Montmorillonite has a high cation exchange capacity, which makes it have a strong buffer capacity to exogenous acids. This study helps to explain the dissolution process of montmorillonite in inorganic and organic acid solutions at different pH value.

Stable hierarchical ionic liquid nanochannels for highly efficient CO2 adsorption, separation and conversion

Constructing stable nanochannels and nanoconfined environments for ionic liquids holds significant application value in gas separation, ion channels, and related fields. The functional polyionic liquid synthesized in this study exhibits a controllable assembly structure and demonstrates liquid crystal properties. Through heating and water treatment, the polyionic liquids crosslink to form multi-hierarchical nanopores, including sub-nanochannels with pore sizes similar to CO2, without the need for a catalyst. The specific surface area and pore size of the polyionic liquid network (PILC) were adjusted by regulating the self-assembly of polyionic liquids in water. The unique PILC, combining ionic liquid nanopores and liquid crystal structure properties, shows high CO2 adsorption performance and excellent CO2/N2 selectivities, surpassing commonly reported ionic liquid porous materials. Furthermore, PILC-2 exhibits good catalytic performance for CO2 cycloaddition, and its catalytic activity and selectivity did not significantly decrease after five cycles. This study successfully introduces hierarchical ionic liquid nanochannels into porous networks without involving any inorganic ordered nanomaterials. This provides a simple and effective approach for the highly selective adsorption and separation of CO2, as well as for the preparation of catalytic materials.

(Invited) Towards Non-Blinking Strongly Confined Perovskite Quantum Dots

Quantum information science has shown its capabilities to enable secure quantum communications. Single photon emitters (SPEs) that emit photons one at a time are fundamental elements of such transformative technologies. Colloidal cesium lead halide (CsPbX3, X=Br, I) perovskite QDs are ideal for next-generation SPEs because of their high room-temperature luminescence efficiency and low-cost, scalable syntheses. Unfortunately, individual perovskite QDs show insufficient photostability and severe photoluminescence (PL) intensity fluctuations (also called blinking). This has greatly limited the spectroscopic studies of perovskite QDs for SPE developments. One major roadblock toward non-blinking, photostable perovskite QDs is their highly ionic crystal structure. When preparing single perovskite QD samples, QD colloids often need to be diluted. During this process ligands can detach from the QD, introducing defects. This is particularly detrimental to strongly confined perovskite QDs since exciton-surface lattice interaction is greatly enhanced. As a result, strongly size confined perovskite QDs are experiencing severe PL blinking with large PL “OFF” occurrences.To suppress perovskite QD blinking and photodegradation, we embedded QDs in an organic crystal matrix consists of Phenethylammonium bromide (PEABr) salts. The bromide rich surface of a QD can be epitaxially anchored onto the PEABr crystals and therefore be stabilized. Individual strongly confined CsPbBr3 QDs in our matrix show nearly non-blinking behavior under non-resonant laser excitations at room temperature. These QDs remain photostable without PL intensity decrease and spectral shift after more than 12 hours of continues excitations. We anticipate that these QDs will lead to more accurate and detailed study of exciton dynamics and structural-optical property relationships in strongly confined perovskite QDs.

Preparation, thermal properties, and structures of ionic plastic crystals with sandwich and half-sandwich Ru complexes

We have recently been investigating the phase behavior of salts of cationic sandwich complexes in pursuit of novel ionic plastic crystals (IPCs). In this study, we synthesized salts containing sandwich complexes [Ru(Cp)(C6H6)]X ([1]X; X = CPFSA− (1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide), SbCl6−) and half-sandwich complexes [Ru(Cp)(DMSO)3]X ([2]X; X = CPFSA−, FSA− ((FSO2)2N−), PF6−). In addition, we examined their thermal properties and crystal structures. Among them, [1]CPFSA exhibited an IPC phase between 365 and 630 K, whereas the others did not undergo phase transitions at 123–403 K. The cations and anions were alternately arranged in the crystals of [1]X, whereas [2]X did not exhibit the alternating arrangement except for [2]PF6. The results showed that alternating molecular arrangements are crucial for the IPC formation, although low symmetry of the ion environment and intermolecular steric hindrance may inhibit it.

ZnO Substitution in Argyrodite Li5.5+3xZnxP1‐xOxS4.5‐xBr1.5 Electrolyte with Enhanced Interface Performance for All‐Solid‐State Battery

AbstractArgyrodite sulfide solid electrolytes (SSEs) have been attracting more concentration in ionic conductivity, crystal structure, and mechanical properties. Nevertheless, shortcomings of SSEs like poor air‐vapor stability and interface reactions limit the wider application in batteries. Herein, a double‐element ZnO substitution strategy is applied to enhancing Li5.5PS4.5Br1.5 Argyrodite electrolyte structure stability and property, Li5.5PS4.5Br1.5 electrolyte with a small amount of ZnO substitution to P and S. Li5.5+3xZnxP1‐xOxS4.5‐xBr1.5 solid electrolytes have achieved improved performance, interface composition also has changed, and crystal structure is becoming more stable. Specifically, LPSBr1.5‐4 %ZnO exhibits the most promising comprehensive properties, more expanded lithium pathway and crystal cell size, 2.25 mS cm−1 ionic conductivity at 25 °C, 65 % electronic conductivity decline, and air stability enhancement. Moreover, LPSBr1.5‐4 %ZnO show decent lithium compatibility and dendrite suppression capability, LPSBr1.5‐4 %ZnO can continue cycling for more than 800 h at 0.1 mA cm−2 in Li symmetric cell, and critical current density has reached 1.4 mA cm−2. More importantly, an all‐solid‐state battery (ASSB) with LPSBr1.5‐4 %ZnO electrolyte can cycle with 130 mAh g−1 capacity and more than 120 cycles in LiCoO2|SSE|In‐Li cell. Our work might provide a strategy to promote structure stability and electrochemical durability, and how element substitution affects ionic transport pathway and crystal structure.

Formation of compounds with diverse polyelectrolyte morphologies and nonlinear ion conductance in a two-dimensional nanofluidic channel.

Aqueous electrolytes subjected to angstrom-scale confinement have recently attracted increasing interest because of their distinctive structural and transport properties, as well as their promising applicability in bioinspired nanofluidic iontronics and ion batteries. Here, we performed microsecond-scale molecular dynamics simulations, which provided evidence of nonlinear ionic conductance under an external lateral electric field due to the self-assembly of cations and anions with diverse polyelectrolyte morphologies (e.g., extremely large ion clusters) in aqueous solutions within angstrom-scale slits. Specifically, we found that the cations and anions of Li2SO4 and CaSO4 formed chain-like polyelectrolyte structures, whereas those of Na2SO4 and MgSO4 predominantly formed a monolayer of hydrated salt. Additionally, the cations and anions of K2SO4 assembled into a hexagonal anhydrous ionic crystal. These ion-dependent diverse polyelectrolyte morphologies stemmed from the enhanced Coulomb interactions, weakened hydration and steric constraints within the angstrom-scale slits. More importantly, once the monolayer hydrated salt or ionic crystal structure was formed, the field-induced ion current exhibited an intriguing gating effect at a low field strength. This abnormal ion transport was attributed to the concerted movement of cations and anions within the solid polyelectrolytes, leading to the suppression of ion currents. When the electric field exceeded a critical strength, however, the ion current surged rapidly due to the dissolution of many cations and anions within a few nanoseconds in the aqueous solution.

An Insight into Halide Solid-State Electrolytes: Progress and Modification Strategies

Tremendous studies have been engaged in exploring the application of solid-state electrolytes (SSEs) as it provides opportunities for next-generation batteries with excellent safety and high energy density. Among the existing SSEs, newly developed halide SSEs have become a hot spot owing to their high ionic conductivity up to 1 mS cm −1 and their stability against high-voltage cathode. As a result, halide SSEs have been shown to be promising candidates for all-solid-state lithium batteries (ASSLBs). Here, we review the progress of halide SSEs and available modification strategies of halide SSE-based batteries. First, halide SSEs are divided into four different categories, including halide SSEs with divalent metal, trivalent metal, tetravalent metal, and non-metal central elements, to overview their progress in the studies of their ionic conductivity, crystal structure, conductive mechanism, and electrochemical properties. Then, based on their existing drawbacks, three sorts of modification strategies, classified as chemical doping, interfacial modification, and composite electrolytes, along with their impacts on halide SSE-based batteries, are summarized. Finally, some perspectives toward halide SSE research are put forward, which will help promote the development of halide SSE-based batteries.

Effects of ionic polarizability and crystal structure on microwave dielectric properties of RE2O3 (RE = La, Eu) ceramics with opposite τ and high Q

Effects of ionic polarizability and crystal structure on microwave dielectric properties of RE2O3 (RE = La, Eu) ceramics with opposite τ and high Q

CsPbBr3@PbBrOH 3D/1D molecular matrix for a high-performance scintillator

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have become highly sought-after materials for X-ray detection and imaging because of their outstanding intrinsic electronic and optical properties. However, because of their highly ionic crystal structure, perovskite materials suffer severe moisture, thermal, and photo instability problems, which hinder their commercialization. To resolve this annoying problem, three-dimensional (3D)/1D CsPbBr3@PbBrOH composite structures in terms of molecular structure are designed by incorporating highly luminescent 3D CsPbBr3 NCs into a 1D PbBrOH matrix to form an “emitter-in-matrix”. The prepared CsPbBr3@PbBrOH exhibits excellent stability without sacrificing photoluminescence quantum yield. Meanwhile, 1D PbBrOH can be considered a perfect host, and the presence of heavy atom Pb in its matrix enhances X-ray absorption. The luminescent CsPbBr3 NCs embedded in an inert PbBrOH host are subjected to X-ray detection and imaging. The CsPbBr3@PbBrOH scintillator shows bright radiation luminescence and sensitive response to X-ray signals. In addition, the scintillator is made into a thin film screen for imaging, obtaining a clear image of the transmission electron microscopy grid hidden inside the capsule, and the resolution of CsPbBr3@PbBrOH film is calculated to be as high as 50 lp mm−1. This property of CsPbBr3@PbBrOH scintillators demonstrates their promising application prospects for ionizing radiation detection, particularly for X-ray imaging.

Insight into the structure and transport properties of pyrrolidinium-based geminal dicationic-organic ionic crystals: unravelling the role of alkyl-chain length.

The present study has been undertaken with an aim to design and develop safer and more efficient all solid-state electrolytes, so that the issues associated with the use of conventional room temperature ionic liquid-based electrolytes can be tackled. To fulfil this objective, a series of geminal di-cationic Organic Ionic Crystals (OICs), based on C3-, C6-, C8- and C9-alkylbridged bis-(methylpyrrolidinium)bromide are synthesized, and the structural features, thermal properties and phase behaviours of these as synthesized OICs have been investigated. Additionally, a number of electro-analytical techniques have been employed to assess their suitability as an efficient electrolyte composite (OIC:I2:TBAI) for all solid-state dye sensitised solar cells (DSSCs). The structural analysis has revealed that along with excellent thermal stability and well-defined surface morphology, all thsese OICs exhibit a well-ordered three-dimensional network of cations and anions that can serve as a conducting channel for the diffusion of iodide ions. Electrochemical investigations have shown that OICs with an intermediate length of alkyl bridge (C6- and C8-alkyl bridged) show better electrolytic performance than those that are based on OICs with a relatively shorter (C3-) or longer (C9-) alkyl-bridge chain. A careful analysis of the above data has essentially demonstrated that the length of the alkyl bridge chain plays a significant role in determining the structural organisation, morphology and eventually the ionic conductivity of OICs. Overall, the comprehensive knowledge on OICs that has been extracted from the current study is expected to be helpful to explore further new types of OIC-based all solid-state electrolytes with improved electrolytic performance for targeted applications.

Mechanism of ionic polarizability, bond valence, and crystal structure on the microwave dielectric properties of disordered Li10MTi13O32 (M = Zn, Mg) spinels

The influence mechanism of the microwave dielectric properties of disordered spinels Li10MTi13O32 (M = Zn, Mg) was investigated via structural refinement, ionic polarizability, bond valence, P–V–L theory, Raman spectroscopy, and DC conductivity.

Investigating the Li+ substructure and ionic transport in Li10GeP2-xSbxS12 (0 ≤ x ≤ 0.25).

Understanding the correlation between ionic motion and crystal structure is crucial for improving solid electrolyte conductivities. Several substitution series in the Li10GeP2S12 structure have shown a favorable impact on the ionic conductivity, e.g. the replacement of P(+V) by Sb(+V) in Li10GeP2S12. However, here the interplay between the structure and ionic motion remains elusive. X-Ray diffraction, high-resolution neutron diffraction, Raman spectroscopy and potentionstatic impedance spectroscopy are employed to explore the impact of Sb(+V) on the Li10GeP2S12 structure. The introduction of antimony elongates the unit cell in the c-direction and increases the M(1)/P(1) and Li(2) polyhedral volume. Over the solid solution range, the Li+ distribution remains similar, an inductive effect seems to be absent and the ionic conductivity is comparable for all compositions. The effect of introducing Sb(+V) in Li10GeP2S12 cannot be corroborated.

Research on the Correlation Between the Lattice Enthalpy of Ionic Compounds and Melting Points

Ionic compounds own different crystal structures from molecular compounds due to the electrostatic force, generating affinities between cations and anions. The lattice energies are made strong and require large energy to break the solids. This paper is used to illustrate the influence of different factors on lattice enthalpy, and correlations between lattice enthalpy and melting points, Regarding carbon fibers as templates, trying to find out if there were theoretically possibilities to utilize ionic crystals more in industrial engineering. Several graphs are made based on the database. Research shows that ion charges are direct proportional to the strength of lattice energy; while ionic radius own inverse relationships. However, unexpected results have been found toward melting points, claiming no obvious effect is made by lattice energies. The reason might contribute to the ideal assumption in terms of lattice enthalpy, assuming they were all in perfect form.

(Digital Presentation) Phosphonium Salts As Potential Guest Substances for Ionic Semiclathrate Hydrates

Semiclathrate hydrates (SCHs) are ionic crystalline compounds consisting of an organic guest cation in several cages formed by hydrogen bonding of water1. SCHs have recently been considered for application to air conditioning systems and refrigeration systems since desirable equilibrium temperatures and the considerable decomposition enthalpies are observed in the solid-liquid equillibria2. Ionic guest substances of SCHs include quaternary onium compounds such as tetrabutylammonium2 and tetrabutylphosphonium based salts3. We report here the preparation and thermodynamic properties of SCHs based on quaternary phosphonium bromides containing an unsaturated carbon-carbon double bond, as shown in Fig. 1, in comparison with the conventional saturated phosphonium salt, such as tetrabutylphosphonium bromide (P4444-Br).The unsaturated phosphonium bromides (P444(1All)-Br and P444(2All)-Br) were synthesized by quaternarization reaction of tributylphosphine with alkenyl bromides in a nitrogen atmosphere. The aqueous solutions were prepared from 5 to 50 w/w %. After thorough stirring, the aqueous solutions were cooled in a freezer to form SCHs. The SCHs were immersed into a thermostatic bath at 268 K for at least 1 day. The temperature in the thermostatic bath was raised from 268 K at a rate of 0.1 K/step (1 step: more than 5 h). The equilibrium temperatures were defined as the temperature at which SCHs were completely dissolved. The ionic crystal structure was analyzed by a powder X-ray diffraction (PXRD) technique, the dissociation enthalpy was measured by a micro differential scanning calorimeter (μDSC).Fig. 2 depicts the solid-liquid phase equilibrium diagram representing the phase equilibrium temperatures of SCHs. The equilibrium temperature of P444(1All)-Br SCH was higher than P4444-Br SCH. These results might be due to the steric effect of alkenyl group. As shown in Fig. 3, the ionic crystal structure of both P444(1All)-Br and P444(All)-Br SCHs were orthorhombic. The dissociation enthalpy of P444(1All)-Br SCHs and P444(2All)-Br SCHs were 188 J/g and 199 J/g, respectively. The unsaturated phosphonium bromides would be regarded as potential guest substances used for latent heat storage materials in air conditioning systems.References M. Oshima, et al, J. Chem. Thermodynamics, 90, 277 (2015).H. Oyama, et al, Fluid Phase Equilibria, 234, 131 (2005).J. Shimada, et al, Chem. Eng. Sci., 236, 116514 (2021). Figure 1

Crystal structure of novel [Ni(2aepy)(2ampy)Cl(H2O)]Cl·H2O complex comprising both 2-aminoethylpyridine (2aepy) and 2-aminomethylpyridine (2ampy) ligands within the coordination sphere and comparison of its thermal properties with analogous Ni(II) complexes with 2ampy and 2aepy ligands

Nickel(II) chloride in the presence of both 2ampy and 2aepy yielded a novel heteroleptic complex [Ni(2aepy)(2ampy)Cl(H2O)]Cl·H2O (1). Its ionic crystal structure is built up of complex cations [Ni(2aepy)(2ampy)Cl(H2O)]+, chloride anions and water solvate molecules. Within the complex cation both 2ampy and 2aepy are coordinated to the Ni(II) atom and its hexacoordination is completed by chlorido and aqua ligands. The supramolecular structure of 1 is built up of 2D hydrogen bonded system. Thermal properties of 1 and two additional analogous nickel(II) complexes, namely [Ni(2ampy)2(H2O)2]Cl2 (2), and [Ni(2aepy)2Cl(H2O)]Cl·H2O (3) were studied in air up to 800 °C. Analysis of the weight losses coupled with MS analyses of the evolved gases and with IR study of the solid intermediates have shown that the thermal decompositions of all complexes 1–3 start with dehydration and continues by decomposition of the aminoalkylpyridine ligands. Only in the case of 2 formation of dehydrated compound [Ni(2ampy)2Cl2] is indicated. The order of the thermal stabilities of the respective complexes is 3 > 2 > 1 according to the starting temperatures of dehydration.