Topochemical Reaction Research Articles

Bi12O17Cl2 with a Sextuple BiO Layer Composed of Rock‐Salt and Fluorite Units and its Structural Conversion through Fluorination to Enhance Photocatalytic Activity

AbstractLayered bismuth oxyhalides with bilayered (Bi2O2) fluorite (FL) slabs are promising visible‐light photocatalysts because of their excellent stability and the ability to adjust band levels depending on the layers combined. It is interesting to manipulate the Bi2O2 slab itself, but only trilayered FL blocks (e.g., Bi3O4) are reported so far. Here, a structurally uncharacterized Bi12O17Cl2, which is extensively studied as a photocatalyst for a variety of reactions, has a sextuple Bi6O8.5 block separated by Cl is shown. Unlike double and triple layered cases, the inner region of the Bi6O8.5 block contains 1D rock‐salt (RS) units in the FL matrix along the a‐axis, causing in‐plane corrugation. A topochemical reaction involving anion‐exchange gives Bi12O17–0.5xFxCl2 (x ≤ 6) with alternate FL and RS slabs along the c‐axis. The elimination of the structural corrugation increases higher photo‐conductivity and improves photocatalytic activity against acetic acid decomposition under visible light irradiation. This study paves new opportunities of controlling the properties of layered bismuth oxyhalides by the thickness of Bi–O block, FL/RS configuration, and structural modulation.

Topochemical intercalation reactions of ZrSe3

Intercalation of alkali and alkaline earth metals into ZrSe3 via soft chemical routes injects electrons and has a significant effect on the selenide-selenide bonding. K, Rb and Cs intercalates of ZrSe3 prepared at low temperatures (−78 ​°C) from metal ammonia solutions contrast with related polymorphs obtained at high temperature (850 ​°C). KxZrSe3 synthesised at low temperatures crystallises in orthorhombic Cmc21, while the polymorph obtained at high temperatures crystallises in Immm. The two structures prepared under drastically different conditions differ by relative shifting of ZrSe3 layers. In contrast, CsxZrSe3 shows the Immm polymorph at low temperature and the Cmc21 polymorph at high temperatures, while a single RbxZrSe3 polymorph in Immm is formed at both temperatures. Intercalation of Ca from liquid ammonia facilitates the co-intercalation of the solvent because of the strong solvation of Ca2+. This compound has severe faulting due to the flexibility in the relative shifts of adjacent ZrSe3 layers.

Continuously Doping BiM2Sr2CaCu2O8+δ into Electron-Doped Superconductor by CaH2 Annealing Method

As a typical hole-doped cuprate superconductor, Bi2Sr2CaCu2O8 + δ (Bi2212) carrier doping is mostly determined by its oxygen content. Traditional doping methods can regulate its doping level within the range of hole doping. Here we report the first application of CaH2 annealing method in regulating the doping level of Bi2212. By continuously controlling the anneal time, a series of differently doped samples can be obtained. The combined experimental results of x-ray diffraction, scanning transmission electron microscopy, resistance and Hall measurements demonstrate that the CaH2 induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range, even switching from hole doping to electron doping. We also found evidence of a low-T c superconducting phase in the electron doping side.

Calorimetric Study of High-Volume Fly Ash-Cement Paste Hydration at Different Temperatures

The study on the hydration process of cement-based materials is of significance since it determines the development of the macro-properties. The hydration process of high-volume fly ash (FA)-cement based materials is quite special and needs systematic study. In this study, the hydration heat release of cement paste with high volume FA were measured with isothermal calorimetry at different temperatures. The full-width at half-maximum (FWHM) value of the exothermic peak and the cementitious index (CMI) of FA were used comprehensively to evaluate the influence of FA on cement hydration. It was found that increasing the FA content and water-binder ratio retarded the hydration process for paste but did not show obvious effects on the hydration of cement. The CMI values show that raising the temperature intensified the retarding effect of FA on cement hydration during the induction period, but promoted the subsequent hydration process. According to the normalized heat release to cement, and the change of CMI values with temperature, new evidence was found that FA may not act as nucleation sites during the hydration process of cement. The result can be better explained by the topochemical reaction mechanism.

Characterisation of enzyme catalysed hydrolysation stage of poly(lactic acid) fibre surface by nanoscale thermal analysis: New mechanistic insight

Enzyme catalysed hydrolysis of bio-based poly(lactic acid) (PLA) represents an environmentally-friendly route for a controlled modification of polymer fibres. In this work, the topochemical hydrolysis reaction of cutinase from Humicola insolens (HiC) on PLA fibre was mechanistically investigated using the advanced surface sensitive nanoscale thermal analysis (nano-TA) technique. The enzymatic hydrolysis preferentially occurs at the amorphous regions of the fibre outer layer, thus leading to randomised hydrolysis, monomer release and ablation of the fibre surface during the initial phase of the hydrolysis. Due to the higher hydrolysis rate at amorphous regions, the crystallinity of the fibre outer layer increases. As a result, an enrichment in overall fibre crystallinity is observed by increased melting enthalpy. The accessibility of the enzyme to the fibre core is restricted, thus the change in crystallinity is prevalent on the fibre outer region. The observed increase of the surface softening temperature from the glass transition temperature close to the melting on-set of crystalline PLA as detected by nano-TA supports the hypothesis, that selective hydrolysis preferably takes place at the amorphous region at the fibre outer layer, thus leading to modified PLA fibres with an unchanged fibre core and a very thin and highly crystalline surface layer.

Crystal Engineering of Pharmaceutical Cocrystals in the Discovery and Development of Improved Drugs.

The subject of crystal engineering started in the 1970s with the study of topochemical reactions in the solid state. A broad chemical definition of crystal engineering was published in 1989, and the supramolecular synthon concept was proposed in 1995 followed by heterosynthons and their potential applications for the design of pharmaceutical cocrystals in 2004. This review traces the development of supramolecular synthons as robust and recurring hydrogen bond patterns for the design and construction of supramolecular architectures, notably, pharmaceutical cocrystals beginning in the early 2000s to the present time. The ability of a cocrystal between an active pharmaceutical ingredient (API) and a pharmaceutically acceptable coformer to systematically tune the physicochemical properties of a drug (i.e., solubility, permeability, hydration, color, compaction, tableting, bioavailability) without changing its molecular structure is the hallmark of the pharmaceutical cocrystals platform, as a bridge between drug discovery and pharmaceutical development. With the design of cocrystals via heterosynthons and prototype case studies to improve drug solubility in place (2000-2015), the period between 2015 to the present time has witnessed the launch of several salt-cocrystal drugs with improved efficacy and high bioavailability. This review on the design, synthesis, and applications of pharmaceutical cocrystals to afford improved drug products and drug substances will interest researchers in crystal engineering, supramolecular chemistry, medicinal chemistry, process development, and pharmaceutical and materials sciences. The scale-up of drug cocrystals and salts using continuous manufacturing technologies provides high-value pharmaceuticals with economic and environmental benefits.

Frontispiece: Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures?

Polymorphism In their Research Article (e202200954), Kana M. Sureshan et al. report a topochemical reaction yielding polymorphs of triazolyl-linked polyinositol.

Frontispiz: Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures?

Polymorphie In ihrem Forschungsartikel (e202200954) berichten Kana M. Sureshan et al. über eine topochemische Reaktion, die Polymorphe von Triazolyl-verknüpftem Polyinositol liefert.

Kinetic Control of Anion Stoichiometry in Hexagonal BaTiO3

The cubic oxyhydride perovskite BaTiO3−xHx, where the well-known ferroelectric oxide BaTiO3 is partially hydridized, exhibits a variety of functions such as being a catalyst and precursor for the synthesis of mixed-anion compounds by utilizing the labile nature of hydride anions. In this study, we present a hexagonal version, BaTi(O3−xHx) (x < 0.6) with the 6H-type structure, synthesized by a topochemical reaction using hydride reduction, unlike reported hexagonal oxyhydrides obtained under high pressure. The conversion of cubic BaTiO3 (150 nm) to the hexagonal phase by heat treatment at low temperature (950~1025 °C) using a Mg getter allows the introduction of large oxygen defects (BaTiO3−x; x − 0.28) while preventing the crystal growth of hexagonal BaTiO3, which has been accessible at high temperatures of ~1500 °C, contributing to the increase of the hydrogen content. Hydride anions in 6H-BaTiO3−xHx preferentially occupy face-sharing sites, as do other oxyhydrides.

Transition Metal Carbo-Chalcogenide "TMCC:" A New Family of 2D Materials.

Here, a new family of 2D transition metal carbo-chalcogenides (TMCCs) is reported, which can be considered a combination of two well-known families, TM carbides (MXenes) and TM dichalcogenides (TMDCs), at the atomic level. Single sheets are successfully obtained from multilayered Nb2 S2 C and Ta2 S2 C using electrochemical lithiation followed by sonication in water. The parent multilayered TMCCs are synthesized using a simple, scalable solid-state synthesis followed by a topochemical reaction. Superconductivity transition is observed at 7.55 K for Nb2 S2 C. The delaminated Nb2 S2 C outperforms both multilayered Nb2 S2 C and delaminated NbS2 as an electrode material for Li-ion batteries. Ab initio calculations predict the elastic constant of TMCC to be over 50% higher than that of TMDC.

Azide–Alkyne Interactions: A Crucial Attractive Force for Their Preorganization for Topochemical Cycloaddition Reaction

A new class of attractive intermolecular interaction between azide and ethynyl structural entities in a wide range of molecular crystals is reported. This interaction was systematically evaluated by using 11 geometrically different structural motifs that are preorganized to direct a solid-state topochemical azide-alkyne cycloaddition (TAAC) reaction. The supramolecular features of the azide-alkyne interaction were mapped by various crystallographic and quantum chemical approaches. Topological analysis shows the noticeable participation of electron density in the azide⋅⋅⋅alkyne interactions. Interestingly, reorientation of the atomic polarizabilities in vicinal azide and alkyne groups upon interaction in crystals favors soft orbital-guided TAAC reactions. Moreover, various solid-state and gas-phase energy decomposition methods of individual azide⋅⋅⋅alkyne interactions summarize that the strength (varies from -5.7 to -30.1 kJ mol-1 ) is primarily guided by the dispersion forces with a influencing contribution from the electrostatics.

First demonstration of tuning between the Kitaev and Ising limits in a honeycomb lattice.

Recent observations of novel spin-orbit coupled states have generated interest in 4d/5d transition metal systems. A prime example is the state in iridate materials and α-RuCl3 that drives Kitaev interactions. Here, by tuning the competition between spin-orbit interaction (λSOC) and trigonal crystal field (ΔT), we restructure the spin-orbital wave functions into a previously unobserved state that drives Ising interactions. This is done via a topochemical reaction that converts Li2RhO3 to Ag3LiRh2O6. Using perturbation theory, we present an explicit expression for the state in the limit ΔT ≫ λSOC realized in Ag3LiRh2O6, different from the conventional state in the limit λSOC ≫ ΔT realized in Li2RhO3. The change of ground state is followed by a marked change of magnetism from a 6 K spin-glass in Li2RhO3 to a 94 K antiferromagnet in Ag3LiRh2O6.

Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures?

AbstractA rigid inositol‐derived monomer functionalized with azide and alkyne as the complementary reactive groups (CRGs) crystallized as three distinct polymorphsI–III. Despite the unsuitable orientation of CRGs in the crystals for complete polymerization, all the three polymorphs underwent regiospecific and quantitative topochemical azide–alkyne cycloaddition (TAAC) polymerization upon heating to yield three different polymorphs of 1,2,3‐triazol‐1,4‐diyl‐linked‐poly‐neo‐inositol. The molecules in these polymorphs exploit the weak intermolecular interactions, free space in the crystal lattice, and heat energy for their large and cooperative molecular motion to attain a transient reactive orientation, ultimately leading to the regiospecific TAAC reaction yielding distinct crystalline polymers. This study cautions that the overreliance on topochemical postulates for the prediction of topochemical reactivity at high temperatures could be misleading.

Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures?

A rigid inositol-derived monomer functionalized with azide and alkyne as the complementary reactive groups (CRGs) crystallized as three distinct polymorphs I-III. Despite the unsuitable orientation of CRGs in the crystals for complete polymerization, all the three polymorphs underwent regiospecific and quantitative topochemical azide-alkyne cycloaddition (TAAC) polymerization upon heating to yield three different polymorphs of 1,2,3-triazol-1,4-diyl-linked-poly-neo-inositol. The molecules in these polymorphs exploit the weak intermolecular interactions, free space in the crystal lattice, and heat energy for their large and cooperative molecular motion to attain a transient reactive orientation, ultimately leading to the regiospecific TAAC reaction yielding distinct crystalline polymers. This study cautions that the overreliance on topochemical postulates for the prediction of topochemical reactivity at high temperatures could be misleading.

Quantum paramagnetism in the hyperhoneycomb Kitaev magnet β−ZnIrO3

A polycrystalline sample of the hyperhoneycomb iridate $\beta$-ZnIrO$_3$ was synthesized via a topochemical reaction, and its structural, magnetic, and thermodynamic properties were investigated. The magnetization and heat capacity data show the absence of long-range magnetic order at least down to 2 K. A positive Curie-Weiss temperature $\theta_W \sim 45$ K probed by the temperature dependence of magnetic susceptibility indicates that a Kitaev interaction is dominant. These observations suggest that a quantum spin liquid may have been realized. Furthermore, the observation of linear temperature-dependent contribution to the heat capacity with no magnetic field effect evidences gapless excitation. These facts are surprisingly contrary to the chemical disorder evidenced by the crystallographic analysis. By discussing the differences in the size effect of Z$_2$-fluxes in 2D and 3D Kitaev magnets, we propose that there is a hidden mechanism to protect the quantum spin liquid state from chemical disorder.

Cuprous delafossites, Cu3(MFeSb)O6 (M = Na, Li) with honeycomb arrays, realized by topochemical ion-exchange reactions

The current work describes the synthesis, structure, magnetic and optical properties of Cu1+ based delafossite oxides, Cu3(MFeSb)O6 (M = Na, Li) synthesized by the topotactic ion-exchange reactions (around 400 °C) of CuCl with Na4FeSbO6 and Na3LiFeSbO6 in an inert argon atmosphere. The synthetic procedure is significant as the oxides could not be synthesized by the solid state methods. Chemical analysis coupled with energy dispersive spectral analysis confirmed the extent of replacement of Na+ ions by Cu+ ions. A complete exchange of alkali metal ion, Na+ by Cu1+ in the interlayers of these honeycomb oxides has been achieved using a ratio of 1:3 between Na4FeSbO6 and CuCl. An additional exchange of approximately 70 % Na+ ions from the honeycomb arrays is possible by varying the ratio to 1:4. Rietveld refinements (space group C2/c) of the powder X-ray diffraction data have been carried out to ascertain the phase purity and to verify the structure formed by edge shared honeycomb arrays separated by Cu1+ in dumbbell configuration (O–Cu1+-O). X-ray photoelectron spectroscopy analysis confirmed the oxidation states of the constituent ions, specifically copper as Cu1+. A similar method is adopted to synthesize Cu3(LiFeSb)O6 by reacting Na3(LiFeSb)O6 and CuCl in the ratio 1:3 at 400 °C. These new delafossite oxides, Cu3(MFeSb)O6 (M = Na, Li) and Cu3((Cu0.7Na0.3)FeSb)O6, exhibit interesting magnetic properties which are significantly different from the rock salt based parent sodium analogs. Dominant antiferromagnetic interactions with a specific ordering temperature have been observed for these samples containing Fe3+ (d5) ions in the honeycomb. UV–visible diffuse reflectance measurements indicated the decrease in the band gap of Cu1+ based oxides. This study highlights the importance of low temperature ion-exchange reactions as an effective route to stabilize multifunctional materials of potential importance for various applications.

Thermal analysis of MgFe-Cl Layered doubled hydroxide (LDH) directly synthetized and produced \u201cvia memory effect\u201d

Layered doubled hydroxides (LDHs) are known to be an interesting class of 2D layered materials, with a wide range of possible composition and a flexible structure suitable for topochemical reactions. Thus, LDHs have been applying in different fields, such as catalysis, energy storage and all the applications in which a high exchange capability (of both cations and anions) is required. For remediation purpose, a MgFe-Cl LDH {[({mathrm{Mg}}_{0.66}^{2+}{mathrm{Fe}}_{0.33}^{3+}{left(mathrm{OH}right)}_{2}]}^{0.33+}{({mathrm{Cl}}_{0.33}^{-})}^{0.33-} (MFC in the following) could be a promising candidate to capture the toxic CrO42− from water, in exchange with the Cl− in an efficient way. The synthesis of this compound might seem simple, consisting of a coprecipitation reaction, and actually, it is strongly affected by the environmental carbon dioxide able to replace the Cl− with the more stable CO32−. To avoid this problem, LDHs could be also prepared with a rehydration of their calcinated oxide (memory effect). In this work were prepared two samples of MFC: one via coprecipitation (MFC-1 in the following) and one via “memory effect” (MFC-mem in the following). Both the compounds were characterized by means of X-ray powder diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR) and differential thermal analysis-thermogravimetry (DTA-TG) coupled with evolved gas analysis. The results demonstrated that the synthesis of pure MFC is very difficult, and only a minimum contamination of carbon dioxide led to the formation of the carbonate LDH in a massive way. It was also demonstrated that Mg-Fe LDHs in the presence of carbonate could catalyse the formation of the formic acid (HCOOH) at low temperature (< 300 °C).

Controllable preparation of two-dimensional oriented BaTiO3 polycrystals from K0.8Ti1.73Li0.27O4 crystals by a one-step solvothermal process

Titanate precursors play an important role in obtaining oriented titanate materials via topochemical conversion. In this study, a two-dimensional (2D) K0.8Ti1.73Li0.27O4 (KTLO) crystal was successfully prepared by a one-step solvothermal process using TiO2, LiOH・H2O, and KOH as raw materials in ethanol/water mixed solvent for the first time. Meanwhile, the conditions and influencing factors for the solvothermal preparation of KTLO were investigated and analysed. With a ratio of ethanol/water of 20:5, better 2D KTLO can be obtained by reacting at 150 °C for 24 h. On this basis, KTLO was used directly to perform solvothermal treatment with Ba(OH)2, and 2D BaTiO3 (BT) was easily prepared by adjusting the reaction conditions (concentration, temperature, and time). When the solvothermal treatment was carried out in 0.5 mol/L Ba(OH)2 solution at 80 °C for 1.5 h, 2D BT crystals could be easily obtained through the topochemical reaction mechanism. This strategy not only develops new methods for preparing precursors but also greatly simplifies the preparation process of BT and provides new research ideas for the preparation of functional materials.

Insights into Sorption-Mineralization Mechanism for Sustainable Granular Composite of MgO-CaO-Al2O3-SiO2-CO2 Based on Nanosized Adsorption Centers and Its Effect on Aqueous Cu(II) Removal.

Although copper is needed for living organisms at low concentrations, it is one of the pollutants that should be monitored along with other heavy metals. A novel and sustainable composite mineralizing sorbent based on MgO-CaO-Al2O3-SiO2-CO2 with nanosized adsorption centers was synthesized using natural calcium–magnesium carbonates and clay aluminosilicates for copper sorption. An organometallic modifier was added as a temporary binder and a source of inovalent ions participating in the reactions of defect formation and activated sintering. The sorbent-mineralizer samples of specified composition and properties showed irreversible sorption of Cu2+ ions by the ion exchange reactions Ca2+ ↔ Cu2+ and Mg2+ ↔ Cu2+. The topochemical reactions of the ion exchange 2OH− → CO32−, 2OH− → SO42− and CO32− → SO42− occurred at the surface with formation of the mixed calcium–copper carbonates and sulfates structurally connected with aluminosilicate matrix. The reverse migration of ions to the environment is blocked by the subsequent mineralization of the newly formed interconnected aluminosilicate and carbonate structures.

Crystalline Fully Carboxylated Polyacetylene Obtained under High Pressure as a Li-Ion Battery Anode Material.

Substituted polyacetylene is expected to improve the chemical stability, physical properties, and combine new functions to the polyacetylene backbones, but its diversity is very limited. Here, by applying external pressure on solid acetylenedicarboxylic acid, we report the first crystalline poly-dicarboxylacetylene with every carbon on the trans-polyacetylene backbone bonded to a carboxyl group, which is very hard to synthesize by traditional methods. The polymerization is evidenced to be a topochemical reaction with the help of hydrogen bonds. This unique structure combines the extremely high content of carbonyl groups and high conductivity of a polyacetylene backbone, which exhibits a high specific capacity and excellent cycling/rate performance as a Li-ion battery (LIB) anode. We present a completely functionalized crystalline polyacetylene and provide a high-pressure solution for the synthesis of polymeric LIB materials and other polymeric materials with a high content of active groups.