Ionic liquids (ILs) and deep eutectic solvents (DESs) have proven to be suitable solvents and reactants for low-temperature reactions. To date, several attempts were made to apply this promising ...class of materials to metal oxide chemistry, which, conventionally, is performed at high temperatures. This review gives an overview about the scientific approaches of the synthesis as well as the dissolution of metal oxides in ILs and DESs. A wide range of metal oxides along with numerous ILs and DESs are covered by this research. With ILs and DESs being involved, many metal oxide phases as well as different particle morphologies were obtained by means of relatively simple reactions paths. By the development of acidic task-specific ILs and DESs, even difficultly soluble metal oxides were dissolved and, hence, made accessible for downstream chemistry. Especially the role of ILs in these reactions is in the focus of discussion.
Ionic liquids and deep eutectic solvents are of growing interest as solvents for the resource‐efficient synthesis of inorganic materials. This Review covers chemical reactions of various deep ...eutectic solvents and types of ionic liquids, including metal‐containing ionic liquids, BF4−‐ or PF6−‐based ionic liquids, basic ionic liquids, and chalcogen‐containing ionic liquids. Cases in which cations, anions, or both are incorporated into the final products are also included. The purpose of this Review is to raise caution about the chemical reactivity of ionic liquids and deep eutectic solvents and to establish a guide for their proper use.
The chemical reactivity of ionic liquids and deep eutectic solvents can intentionally be exploited as a synthetic tool to prepare inorganic materials that are difficult or even impossible to obtain by traditional synthetic routes. This Review summarizes recent developments in inorganic syntheses that take advantage of reactions with ionic liquids or deep eutectic solvents.
Due to their typically low reactivity, the activation of metal oxides, as found in ores, earths and minerals, is in general performed by high temperature reactions, which consume much energy. Owing ...to the prevalence of fossil fuels, this is accompagnied by the generation of large amounts of CO
2
. Alternatively, ionic liquids (ILs) can be used as solvents for metal oxide dissolution and downstream chemistry at much lower temperatures. The dissolution ability of the dry ionic liquid betainium bis(trifluoromethylsulfonyl)imide, HbetNTf
2
, was investigated for 30 metal oxides at 175 °C and compared to chloride containing IL Hbet
2
NTf
2
Cl. A general dissolution-promoting effect of chloride anions was found, regarding reaction time as well as the variety of dissolved metal oxides. Up to now, the dissolution in Hbet
2
NTf
2
Cl is limited to basic or amphoteric metal oxides and assumed to be influenced by multiple factors, such as reaction conditions and the lattice energy of the metal oxide as well as its crystal structure. Comprehensive investigations were performed for the dissolution of CuO, which led to the discovery of the water-free complex compound Cu
2
(bet)
4
(NTf
2
)
2
NTf
2
2
. Proceeding from this compound, a complete exchange of the O-coordination sphere by other ligands was demonstrated, opening up promising possibilities for downstream chemistry.
Investigation on the dissolution of 30 metal oxides in the water-free ionic liquid HbetNTf
2
and the catalytic effect of chloride for the application in green ore processing.
Polyalcohols (polyols), such as ethylene glycol, have mild reducing ability. They are used in the so‐called polyol process to produce metallic nanoparticles of various kinds. In these syntheses, the ...effective reduction potential of the polyol strongly depends on the presence of other anions. Those anions compete against the polyol molecules for the direct bonding to the metal cations. As an indicator for the coordination behavior of polyols, we crystallized and structurally characterized 19 new coordination compounds with Mn, Co, Ni, Cu, Zn, Cd, Pb, or Bi. 15 of these compounds comprise nitrate ions, the others acetate ions. Compared to the already known chloride and sulfate analogues, nitrate shows an intermediate coordination affinity towards the metal cations considered here. While no direct metal–nitrate coordination occurs with Co2+, Ni2+, and Zn2+, mixed nitrate–polyol coordination environments are found for Mn2+, Cu2+, Cd2+, and Bi3+. Because of its strong chelating property, the acetate ion always coordinates the metal cation, competing with the polyol. The first mononuclear and dinuclear metal acetate diol coordination compounds were obtained with Co2+ and Cu2+, respectively. The coordination affinity of nitrate and acetate ligands in solid metal polyol complexes fully corresponds with our recent observations of the anion‐dependent reduction behavior of copper(II) salts in polyols.
The effective reductive potential of polyols depends on the presence of anionic ligands. 19 new coordination compounds of Mn, Co, Ni, Cu, Zn, Cd, Pb, or Bi shed light on the competition between various polyols and nitrate or acetate anions for direct bonding to the metal cation.
• The syntheses and structures of main group polycations are reviewed. • Advantages and limitations of different synthetic approaches are compared. • The benefit of room temperature ionic liquids as ...reaction media is demonstrated.
Polycations of the electron-rich main group elements are interesting in terms of their diverse structural chemistry and chemical bonding. They constitute a well-established class of compounds of intrinsic fascination and have been widely studied in the past. In this contribution, different routes for the synthesis of polycations of groups 15 and 16 are reviewed and their advantages and limitations are briefly compared. It is concluded that the most recent synthesis procedure in ionic liquid media is a good alternative approach due to mild reaction conditions, process economics, simple treatment, high yield and little influence on environment.
High-quality single crystals of MnBi2Te4 are grown for the first time by slow cooling within a narrow range between the melting points of Bi2Te3 (586 °C) and MnBi2Te4 (600 °C). Single-crystal X-ray ...diffraction and electron microscopy reveal ubiquitous antisite defects in both cation sites and, possibly, Mn vacancies (Mn0.85(3)Bi2.10(3)Te4). Thermochemical studies complemented with high-temperature X-ray diffraction establish a limited high-temperature range of phase stability and metastability at room temperature. Nevertheless, the synthesis of MnBi2Te4 can be scaled-up as powders can be obtained at subsolidus temperatures and quenched at room temperature. Bulk samples exhibit long-range antiferromagnetic ordering below 24 K. The Mn(II) out-of-plane magnetic state is confirmed by the magnetization, X-ray photoemission, X-ray absorption, and linear dichroism measurements. The compound shows a metallic type of resistivity in the range 4.5–300 K and is an n-type conductor that reaches a thermoelectric figure of merit up to ZT = 0.17. Angle-resolved photoemission experiments show a surface state forming a gapped Dirac cone, thus strengthening MnBi2Te4 as a promising candidate for the intrinsic magnetic topological insulator, in accordance with theoretical predictions. The developed synthetic protocols enable further experimental studies of a crossover between magnetic ordering and nontrivial topology in bulk MnBi2Te4.
Synthesis near room temperature: Michael Ruck, chair of the priority program “Synthesis near Room‐Temperature” (SPP 1708) of the German Research Foundation (DFG), describes the work carried out ...within the frame of this research program since its establishment in 2014.
Transition-metal chemistry in ionic liquids (IL) has achieved intrinsic fascination in the last few years. The use of an IL as environmental friendly solvent, offers many advantages over traditional ...materials synthesis methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room-temperature IL have been found to be excellent media for stabilising transition-metal clusters in solution and to crystallise homo- and heteronuclear transition-metal complexes and clusters. Furthermore, the use of IL as solvent provides the option to replace high-temperature routes, such as crystallisation from the melt or gas-phase deposition, by convenient room- or low-temperature syntheses. Inorganic IL composed of alkali metal cations and polynuclear transition-metal cluster anions are also known. Each of these areas will be discussed briefly in this contribution.
Bi2S3 was dissolved in the presence of NaCl in the ionic liquid BMImCl ⋅ 4AlCl3 (BMIm=1‐n‐butyl‐3‐methylimidazolium) through annealing the mixture at 180 °C. Upon cooling to room temperature, orange, ...air‐sensitive crystals of Na(Bi7S8)S(AlCl3)32AlCl42 (1) precipitated. X‐ray diffraction on single‐crystals of 1 revealed a triclinic crystal structure that contains (Bi7S8)5+ spiro‐dicubanes, S(AlCl3)32− tetrahedra triples, isolated AlCl4− tetrahedra, and sodium cations.
In an ionothermal synthesis bismuth sulfide reacted to spiro‐dicubane cations (Bi7S8)5+, which crystallized in a complex structured salt. Diverse alkali metal cations were incorporated alongside these polycations, hinting at the existence of a structure family, despite stacking faults preventing a full structure elucidation of all compounds.
A binder-free aluminum (Al) electrode was fabricated by electrodeposition on a three-dimensional copper foam (3DCu) or carbon fabric (3DCF) from a mixed-halide ionic liquid. The strong adhesion, ...structural stability and interface compatibility between Al and 3DCu facilitate high electrical conductivity and effectively alleviate large volume change. In a lithium-ion battery, the continuous, dendrite-free Al/3DCu electrode enables stable and reversible reactions, which delivered a first discharge capacity of 981 mAh g−1 in a coin cell at 21 mA g−1. It operates stably for at least 12 cycles with a discharge depth of about 1 mAh per cycle (7 h each) at the rate of 21 mA g−1. The cycled Al/3DCu electrode maintains good interfacial stability and shows no shedding. In contrast to many nanostructured electrodes, the amount of Al can reach 30% of a solid Al electrode with an average conversion to Li0.71Al. The concept of porous 3D electrodes provides a good compromise between diffusion kinetics and the total amount of active metal available in a battery with alloying-type anodes and appears promising for application.
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