Topotactic Reaction Research Articles

Reversible and Topotactic Solvent Removal in a Magnetic Ni(NCS)2 Coordination Polymer.

Reaction of Ni(NCS)2 with 4-(Boc-amino)pyridine in acetonitrile leads to the formation of a new coordination polymer with the composition Ni(NCS)2(4-(Boc-amino)pyridine)2·MeCN (1-MeCN). In the crystal structure the Ni(II) cations are linked by the anionic ligands into chains that are further connected into layers by intermolecular N-H···O hydrogen bonding. These layers are stacked and channels are formed, in which acetonitrile molecules are located. Solvent removal leads to the ansolvate 1, which shows microporosity as proven by sorption measurements. Single crystal X-ray investigations reveal that the solvent removal leads to a change in symmetry from primitive to C-centered, which is reversible and which proceeds via a topotactic reaction leaving the network intact. The magnetic properties of 1-MeCN and 1 are governed by the ferromagnetic exchange between spins of Ni(II) forming chains. The susceptibility and specific heat for such a quantum Heisenberg chain of S = 1 spins with zero-field splitting are calculated using the DMRG method and compared with the experimental results.

K‐Ion Batteries Based on a P2‐Type K0.6CoO2 Cathode

K‐ion batteries are a potentially exciting and new energy storage technology that can combine high specific energy, cycle life, and good power capability, all while using abundant potassium resources. The discovery of novel cathodes is a critical step toward realizing K‐ion batteries (KIBs). In this work, a layered P2‐type K0.6CoO2 cathode is developed and highly reversible K ion intercalation is demonstrated. In situ X‐ray diffraction combined with electrochemical titration reveals that P2‐type K0.6CoO2 can store and release a considerable amount of K ions via a topotactic reaction. Despite the large amount of phase transitions as function of K content, the cathode operates highly reversibly and with good rate capability. The practical feasibility of KIBs is further demonstrated by constructing full cells with a graphite anode. This work highlights the potential of KIBs as viable alternatives for Li‐ion and Na‐ion batteries and provides new insights and directions for the development of next‐generation energy storage systems.

Tuning the Structure and Ionic Interactions in a Thermochemically Stable Hybrid Layered Titanate‐Based Nanocomposite for High Temperature Solid Lubrication

Solid inorganic lubricants are thermally stable but they are often limited by their lack of deformability, while organic lubricants have limitations in terms of thermal stability. In this study, a novel solid organic–inorganic nanocomposite lubricant that synergistically combines the thermochemically stable structure of a layered oxide with the relative softness of an organic polymer is presented. The nanocomposite is made by intercalating 11‐aminoundecanoic acid in a lepidocrocite‐type protonated titanate, H1.07Ti1.73O4. The amino acid molecules rapidly arrange to form a paraffinic bilayer in the gallery region of the layered host. This topotactic reaction yields a well‐organized layered nanocomposite consisting of inorganic 2D titanate layers separated by amino acid molecules. Above elevated temperatures, 11‐undecanoic acid polymerizes into nylon‐11 confined between crystalline titanate monolayers. The lubricating properties of these nanocomposites up to 580 °C are determined using high‐temperature pin‐on‐disc experiments using steel‐steel contacts. The lubricative properties are based on the softening of the intercalated polymer above 200 °C. The encapsulation of the polymer chains by the inorganic titanate monolayers protects the organic component from thermal degradation and increases the thermal stability of the system.

(Invited) Applying Energy Storage to Tune the Magnetism of Large-Pore Ordered Mesoporous Metal Oxide Thin Films

Polymer-templated mesostructured non-silicate oxide thin films have received much attention in the past on account of their potential for future device applications. However, despite the overall progress made in the synthesis of such materials, “complex” metal oxides are more often than not ill-defined from a structural point of view. The primary reasons are the lack of control over the hydrolysis and condensation reactions of the inorganic precursors used, and the fact that the crystallization of the nanoscale walls is difficult to control. In this talk I will describe the evaporation-induced self-assembly synthesis of cubic mesoporous La1–xCaxMnO3 (LCMO), La1–ySryMnO3 (LSMO) and LiFe5O8 (LFO) thin films using a polyisobutylene-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent. Electron microscopy, GISAXS, XRD, XPS, RBS and SQUID magnetometry all show that these materials are of high quality and thermally stable to over 600 °C. More importantly, they can store charge by topotactic lithium insertion reaction (LFO) and via double-layer capacitance (LCMO/LSMO), which allows for the intriguing possibility of reversibly tuning the magnetization [1, 2]. Collectively, I will show that both approaches provide a method to exert fine control over magnetism in situ, and further might help to better understand (Faradaic) surface charge storage processes. [1] C. Reitz, P. M. Leufke, R. Schneider, H. Hahn, T. Brezesinski, Chem. Mater. 26 (2014) 5745. [2] C. Reitz, C. Suchomski, D. Wang, H. Hahn, T. Brezesinski, J. Mater. Chem. C 4 (2016) 8889.

Two-dimensional metal-phosphorus monohydrides

In the rapidly expanding field of two-dimensional (2D) materials, special attention is given to systems that can be stabilized as free-standing monolayers. Here we use density-functional theory calculations to show how a well-established synthesis route can prepare stable 2D sheets of P-based hydrides. In particular, we show that strongly exothermic topotactic reactions of suitable AlB2-like precursors produce 2D materials with stoichiometries CuPH, AuPH, AgPH and PdPH. This novel family of monolayer systems provides multifunctional building blocks for devices as it includes metals, semimetals (with Dirac-like cones) and semiconductors with small or wide energy band gaps.

Synthesis and thermoelectric characterization of high density Ag2Te nanowire/PMMA nanocomposites

N-type thermoelectric nanocomposites based on monoclinic silver telluride nanowires (Ag2Te NWs) and poly(methyl methacrylate) beads were prepared by means of a simple hot compaction technique. Control of Ag2Te NW composition and crystal structure was achieved by tuning the AgNO3 content in the electrolyte while maintaining a fixed reaction time of the topotactic reaction with Te NWs. The curved shapes and high aspect ratios of the Ag2Te NWs were important in fabricating composites of high density in our system and resulted in reduced contact resistance between the nanowires, which was critical in enhancing the composites' electrical and thermoelectric properties. The thermal conductivity of the composites increased somewhat with nanowire content, but all composites had thermal conductivity nearly the same as that of polymeric material. Consequently, figure of merit (ZT) of 0.005 was achieved in a nanocomposite containing 50 wt% Ag2Te NWs at room-temperature.

Three-dimensional graphene frameworks wrapped Li3V2(PO4)3 with reversible topotactic sodium-ion storage

Li3V2(PO4)3 (LVP) was evaluated as a promising cathode material for sodium-ion batteries (SIBs). The three-dimensional graphene frameworks wrapped LVP (LVP-G-FD) exhibited high energy density of 501.3Whkg−1, which is almost the highest energy density among the known polyanionic cathodes for SIBs. The enhanced electrochemical performance of LVP-G-FD is attributed to the graphene framework which provides the fast electronic transport network and buffering space. Besides, the sodium-ion storage mechanism of LVP was investigated via in-situ XRD and so on. The sodium-ion storage process is composed of the electrochemical topotactic replacement and the subsequent topotactic reaction.

Synthesis of ultra-long cadmium telluride nanotubes via combinational chemical transformation

Synthesis of high-throughput cadmium telluride (CdTe) nanotubes with an ultra-long aspect ratio is presented via a combination process concept combined with electrospinning, electrodeposition, and cationic exchange reaction. Ultra-long sacrificial silver (Ag) nanofibers were synthesized by electrospinning involving two-step calcination, and were then electrodeposited to create silver telluride nanotubes. These nanotubes underwent cationic exchange reaction in cadmium nitrate tetrahydrate solution with the aid of a ligand, tributylphosphine (TBP). Analysis showed that ultra-long pure zinc blende CdTe nanotubes were obtained with controlled dimension and uniform morphology. The thermodynamic driving force induced by the coordination of methanol solvent and TBP attributed to overcome the kinetic barrier between Ag2Te and CdTe nanotubes, facilitating the synthesis of CdTe nanotubes. This synthetic process involving a topotactic reaction route paves a way for high-throughput extended synthesis of new chalcogenide hollow nanotubes for application in photodetectors and solar cells.

One‐Pot Synthesis of [111]‐/{010} Facets Coexisting Anatase Nanocrystals with Enhanced Dye‐Sensitized Solar Cell Performance

AbstractA facile one‐pot hydrothermal synthesis cuboid/rhombic coexisting anatase nanocrystals with a large percentage of [111]‐/{010} facets were reported through using tetratitanate nanoribbons as a precursor. The nanostructures and the formation reaction mechanism of the obtained anatase TiO2 nanocrystals from the layered tetratitanate nanoribbons were investigated by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), and transmission electron microscope (TEM). The transformation from the layered phase into the anatase TiO2 may experience two types of reaction during the hydrothermal reaction, including the in situ topotactic dehydration reaction and the dissolution‐deposition reaction. And the adsorption behavior of N719 Dye on TiO2 surface was studied. Furthermore, the dye‐sensitized solar cell (DSSC) performance of the synthesized [111]‐/{010}‐faceted anatase nanocrystals was also characterized, which showed a superior photovoltaic performance, compared to the commercial P25 TiO2 nanocrystals.

Electrochemical Li Topotactic Reaction in Layered SnP3 for Superior Li-Ion Batteries

The development of new anode materials having high electrochemical performances and interesting reaction mechanisms is highly required to satisfy the need for long-lasting mobile electronic devices and electric vehicles. Here, we report a layer crystalline structured SnP3 and its unique electrochemical behaviors with Li. The SnP3 was simply synthesized through modification of Sn crystallography by combination with P and its potential as an anode material for LIBs was investigated. During Li insertion reaction, the SnP3 anode showed an interesting two-step electrochemical reaction mechanism comprised of a topotactic transition (0.7–2.0 V) and a conversion (0.0–2.0 V) reaction. When the SnP3-based composite electrode was tested within the topotactic reaction region (0.7–2.0 V) between SnP3 and LixSnP3 (x ≤ 4), it showed excellent electrochemical properties, such as a high volumetric capacity (1st discharge/charge capacity was 840/663 mA h cm−3) with a high initial coulombic efficiency, stable cycle behavior (636 mA h cm−3 over 100 cycles), and fast rate capability (550 mA h cm−3 at 3C). This layered SnP3 anode will be applicable to a new anode material for rechargeable LIBs.

ChemInform Abstract: Platelike Ag2Nb4O11 Mesocrystals: Soft Chemical Synthesis, Formation Mechanism and Enhanced Photocatalytic Performance.

AbstractThe title mesocrystals (polycrystals of oriented nanocrystals) are prepared via a soft chemical topotactic reaction using solvothermally prepared layered K4Nb6O17 plate like particles that are first acidified by dilute HNO3 for 24 h and then subjected to an ion exchange in 0.3 M AgNO3 (24 h) which is followed by calcination in air (600 °C, 2 h).

Evaluation of layered zinc hydroxide nitrate and zinc/nickel double hydroxide salts in the removal of chromate ions from solutions

Layered zinc hydroxide nitrate (ZnHN) and Zn/Ni layered double hydroxide salts were synthesized and used to remove chromate ions from solutions at pH 8.0. The materials were characterized by many instrumental techniques before and after chromate ion removal. ZnHN decomposed after contact with the chromate solution, whereas the layered structure of Zn/Ni hydroxide nitrate (Zn/NiHN) and Zn/Ni hydroxide acetate (Zn/NiHA) remained their layers intact after the topotactic anionic exchange reaction, only changing the basal distances. ZnHN, Zn/NiHN, and Zn/NiHA removed 210.1, 144.8, and 170.1mg of CrO42−/g of material, respectively. Although the removal values obtained for Zn/NiHN and Zn/NiHA were smaller than the values predicted for the ideal formulas of the solids (194.3 and 192.4mg of CrO42−/g of material, respectively), the measured capacities were higher than the values achieved with many materials reported in the literature. Kinetic experiments showed the removal reaction was fast. To facilitate the solid/liquid separation process after chromium removal, Zn/Ni layered double hydroxide salts with magnetic supports were also synthesized, and their ability to remove chromate was evaluated.

Improved Topotactic Reactions for Maximizing Organic Coverage of Methyl Germanane

The topotactic transformation of Zintl phases such as CaGe2 into organic-terminated germanium graphane analogues using haloalkanes is a powerful route for generating new 2D optoelectronic and spintronic building blocks. However, uniform ligand coverage is necessary for optimizing the properties and stability of these single-atom-thick frameworks. Here, we compare the effectiveness of different topochemical methods to maximize methyl-termination in GeCH3. We show that a previously developed CH3I/H2O phase transfer route produces a small percentage of partially oxidized germanane. The partially oxidized termination is readily removed upon HCl treatment, which leads to Ge–Cl termination, but rapidly reoxidizes after exposure to the ambient atmosphere. We then show that a one-pot route with CH3I in distilled CH3CN solvent and at least six equivalents of H2O results in no oxidation. The GeCH3 prepared from this one-pot route also has an increased −CH3/–H ratio of termination from ∼90:10 to ∼95:5, is air-stable, has greater thermal stability, has a sharper absorption onset, and has more narrow band edge photoluminescence, all of which are signatures of a less defective semiconductor.

Platelike Ag2Nb4O11 mesocrystals: Soft chemical synthesis, formation mechanism and enhanced photocatalytic performance

The soft chemical process is a useful and unique method for the preparation and design of mesocrystals materials. The platelike Ag2Nb4O11 mesocrystals are prepared via the soft chemical topotactic reaction using the layered structure K4Nb6O17 platelike particles as precursor. The formation mechanism is investigated through tracing the evolution of structure and morphology of intermediate products during the reaction, and it contains two processes. One is the ion-exchange reaction with the interlaminar ions of layered precursor. The other is in situ topotactic structure transformation reaction of the platelike Ag3HNb6O17 into platelike Ag2Nb4O11 mesocrystals during the heat-treatment process. Moreover, the degradation of RhB over the platelike Ag2Nb4O11 mesocrystals can reach to 95.3% after the irradiation of 20 min. The enhancement of photocatalytic performance of Ag2Nb4O11 mesocrystals can be attributed to its unique morphology and exposed facet, which affect the band gap and energy band structure.

Fast Preparation of Dimorphic Thioantimonates and a Thioantimonate with a Hitherto Unknown Network Topology Applying a New Synthesis Approach

The reaction of an aqueous solution of Na3SbS3 with [Ni(terpy)2]2+ (terpy = 2,2′:6′,2″-terpyridine) afforded crystallization of three new thioantimonates in short reaction times. Two polymorphic compounds, [Ni(terpy)2][Sb4S7]·H2O (1, 2), were obtained simultaneously under identical reaction conditions, while an increase of the reaction temperature led to formation of the third compound [Ni(terpy)2]2[Sb10S17] (3). In 1 the anion consists of a [Sb4S7]2– chain, whereas 2 is composed of a layered [Sb4S7]2– anion. Form 2 disappeared at longer reaction times, and therefore modification 1 might represent the thermodynamically stable form at this temperature despite the lower density compared to 2. Storing modification 1 at elevated temperatures the water can partly be removed in a topotactic reaction leading to the compound [Ni(terpy)2][Sb4S7]·0.25 H2O (1A). Compound 3 exhibits a unique Sb:S ratio, and a never before observed network topology significantly enhancing the structural diversity of thioantimonates(III).

Conversion of Marine Structures to Calcium Phosphate Materials: Mechanisms of Conversion Using Two Different Phosphate Solutions

Marine structure, coralline materials were converted to calcium phosphate using two different phosphate solutions. The aim was to study the conversion mechanisms under acidic and basic environment at moderate conditions of temperature. Crystal growth and morphology of converted corals were characterized by XRD and SEM respectively. The results suggested that under acidic conditions (H3PO4), dissolution and precipitation control and direct the crystal formation and morphology in which transition from plate like to rod like hydroxyapatite structure was favoured. Metastable phase such as monetite formed and transformed to HAp during reaction. During the first hour of the dissolution a monetite and hydroxyapatite mixture precipitates and then the full conversion to hydroxyapatite is observed. On the other hand, under basic conditions (NH4)2HPO4, just diffusional surface conversion of the calcium carbonate structure of coralline materials to hydroxyapatite and a very small amount of tri-calcium phosphate is observed. The mechanism can be classified as the solid-state topotactic ion-exchange reaction mechanism.

Vanadium Sulfate As New Electrode Material for Na Ion Batteries

The design of new materials that provide high energy densities and long cycle life together with being economic and environmental benign is crucial for the energy storage. Therefore, the soft chemistry used to prepare the original frameworks, new structures is in perfect appropriateness with such a target. Our research is focused on the synthesis by soft chemistry of new “metastable” frameworks with large tunnels or layered structures at low temperature. We will discuss on our strategies to generate original framework showing ionic conductivity. The first approach is based on topotactic reactions starting from existing ionic conductors with a compact anionic framework [1]. In this case, we will show that the lithium/sodium insertion leads to new rock salt type structure. The second approach is related to polyanionic frameworks [2]. In order to favor reactivity, we are using protonic materials containing transition elements with adequate redox potential (Fe, Mn). We will show for example that lithium or sodium insertion into the jarosite hydroxysulfate phase NaFe3(SO4)2(OH)6 leads to an amorphous phase Na3Fe3(SO4)2(OH)6 which exhibits a reversible electrochemical sodium intercalation/deintercalation through a solid solution-like process, leading back to the jarosite NaFe3(SO4)2(OH)6, at 2.72V and a capacity of 100 mAh/g at C/20. This unique topotactic reaction between an amorphous and a well crystallized phase is interpreted on the basis of the formation of an inorganic polymer and will be discuss in the presentation. V. Pralong, V. Gopal, V. Caignaert, et al., Chem. Mat. Com., 2012, 24, 12; V. Pralong, Progress in Solid State Chem., 2009, 37, 4, 262-277; V. Gopal, V. Pralong, et al., Electrochem. Com., 40, 100-102, 2014; V. Pralong et al., Inorg. Chem., 53, 522, 2014M. A. Reddy, V. Pralong, V. Caignaert, et al., Electrochem. Com., 2009, 11 1807; V. Pralong, V. Caignaert, B. Raveau, J. Mater. Chem., 2011, 21, 12188; M. Gnanavel et al., Chem Mater., 26, 4521, 2014

Prospects of Colloidal Copper Chalcogenide Nanocrystals.

Over the past few years, colloidal copper chalcogenide nanocrystals (NCs) have emerged as promising alternatives to conventional Cd and Pb chalcogenide NCs. Owing to their wide size, shape, and composition tunability, Cu chalcogenide NCs hold great promise for several applications, such as photovoltaics, lighting and displays, and biomedical imaging. They also offer characteristics that are unparalleled by Cd and Pb chalcogenide NCs, such as plasmonic properties. Moreover, colloidal Cu chalcogenide NCs have low toxicity, potentially lower costs, and excellent colloidal stability. This makes them attractive materials for the large-scale deployment of inexpensive, sustainable, and environmentally benign solution-processed devices. Nevertheless, the synthesis of colloidal Cu chalcogenide NCs, especially that of ternary and quaternary compositions, has yet to reach the same level of mastery as that available for the prototypical Cd chalcogenide based NCs. This review provides a concise overview of this rapidly advancing field, sketching the state of the art and highlighting the key challenges. We discuss recent developments in the synthesis of size-, shape-, and composition-controlled NCs of Cu chalcogenides, with emphasis in strategies to circumvent the limitations arising from the need to precisely balance the reactivities of multiple precursors in synthesizing ternary and quaternary compositions. In this respect, we show that topotactic cation-exchange reactions are a promising alternative route to complex multinary Cu chalcogenide NCs and hetero-NCs, which are not attainable by conventional routes. The properties and potential applications of Cu chalcogenide NCs and hetero-NCs are also addressed.

Experimental and theoretical investigation of electronic structure of SrFeO3−xFx epitaxial thin films prepared via topotactic reaction

We investigated the electronic structure of perovskite SrFeO3−xFx (0.6 ≤ x ≤ 1) films by optical absorption, photoemission, and X-ray absorption spectroscopies, as well as density functional theory (DFT)-based calculations. The optical bandgap expanded with x, yielding a wider direct bandgap for the SrFeO2F film than for the LaFeO3 film. The DFT calculations suggested that the majority of FeO4F2 octahedra in the SrFeO2F film had cis configurations and that the enlarged bandgap mainly originated from bond bending in the O–Fe–O chains. We experimentally observed the valence and conduction bands of the SrFeO2F film, and found them to be qualitatively consistent with the results of DFT-based calculations.

Iridium containing honeycomb Delafossites by topotactic cation exchange.

We report the structure and magnetic properties of two new iridium-based honeycomb Delafossite compounds, Cu3NaIr2O6 and Cu3LiIr2O6, formed by a topotactic cation exchange reaction. The starting materials Na2IrO3 and Li2IrO3, which are based on layers of IrO6 octahedra in a honeycomb lattice separated by layers of alkali ions, are transformed to the title compounds by a topotactic exchange reaction through heating with CuCl below 450 °C; higher temperature reactions cause decomposition. The new compounds display dramatically different magnetic behavior from their parent compounds - Cu3NaIr2O6 has a ferromagnetic like magnetic transition at 10 K, while Cu3LiIr2O6 retains the antiferromagnetic transition temperature of its parent compound but displays significantly stronger dominance of antiferromagnetic coupling between spins. These results reveal that a surprising difference in the magnetic interactions between the magnetic Ir ions has been induced by a change in the non-magnetic interlayer species. A combination of neutron and X-ray powder diffraction is used for the structure refinement of Cu3NaIr2O6 and both compounds are compared to their parent materials.