Ionic liquids (ILs) have been proven to be valuable reaction media for the synthesis of inorganic materials among an abundance of other applications in different fields of chemistry. Up to now, the syntheses have remained mostly “black boxes”; and researchers have to resort to trial-and-error in order to establish a new synthetic route to a specific compound. This review comprises decisive reaction parameters and techniques for the directed synthesis of polyions of heavy main-group elements (fourth period and beyond) in ILs. Several families of compounds are presented ranging from polyhalides over carbonyl complexes and selenidostannates to homo and heteropolycations.

The low temperature syntheses of AuTe2 and Ag2Te starting from the elements were investigated in the ionic liquids (ILs) [BMIm]X and [P66614]Z ([BMIm]+=1‐butyl‐3‐methylimidazolium; X = Cl, [HSO4]−, [P66614]+ = trihexyltetradecylphosphonium; Z = Cl−, Br−, dicyanamide [DCA]−, bis(trifluoromethylsulfonyl)imide [NTf2]−, decanoate [dec]−, acetate [OAc]−, bis(2,4,4‐trimethylpentyl)phosphinate [BTMP]−). Powder X‐ray diffraction, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy revealed that [P66614]Cl is the most promising candidate for the single phase synthesis of AuTe2 at 200 °C. Ag2Te was obtained using the same ILs by reducing the temperature in the flask to 60 °C. Even at room temperature, quantitative yield was achieved by using either 2 mol % of [P66614]Cl in dichloromethane or a planetary ball mill. Diffusion experiments, 31P and 125Te‐NMR, and mass spectroscopy revealed one of the reaction mechanisms at 60 °C. Catalytic amounts of alkylphosphanes in commercial [P66614]Cl activate tellurium and form soluble phosphane tellurides, which react on the metal surface to solid telluride and the initial phosphane. In addition, a convenient method for the purification of [P66614]Cl was developed.

PX compounds (X=Cl, Br, I) in imidazolium halide ionic liquids combine with the anion Z (Z=Cl, Br, I) of the solvent to form [PX Z] complex anions. These anions have a sawhorse shape in which the lone pair of the phosphorus atom fills the third equatorial position of the pseudotrigonal bipyramid. Theoretical results show that this association remains incomplete due to strong hydrogen bonding with the cations of the ionic liquid, which competes with the phosphorus trihalide for interaction with the Z anion. Temperature-dependent P NMR experiments indicated that the P-Z binding is weaker at higher temperature. Both theory and experiment evidence dynamic exchange of the halide anions at the phosphorus atom, together with continuous switching of the ligands at the phosphorus atom between equatorial and axial positions. Detailed knowledge of the mechanism of the spontaneous exchange of halogen atoms at phosphorus trihalides suggests a way to design novel, highly conducting ionic-liquid mixtures.

Li-ion conductive polycrystalline Li4B7O12Cl to be used as a solid-state electrolyte was successfully synthesized by an ionothermal route at a low temperature. The reaction of lithium acetate dihydrate, boric acid, and copper­(II) chloride dihydrate in trihexyltetradecylphosphonium chloride at 130 °C led to single-phase Li4B7O12Cl within 10 h. Li4B7O12Br was also successfully synthesized in a similar way. The ionic conductivity, activation energy, and electrochemical window of Li4B7O12Cl electrolyte were measured. A relatively high ionic conductivity of 3 × 10–4 S cm–1 at room temperature was detected. A linear sweep voltammogram of the Li4B7O12Cl electrolyte exhibited an electrochemical stability of up to 4.3 V vs. Li/Li+ under the measured conditions. The fabricated {Li ∥ Li4B7O12Cl ∥ Li} symmetrical cell exhibits a relatively low voltage hysteresis of 120 mV for 60 cycles.

Elemental tellurium readily dissolves in ionic liquids (ILs) based on tetraalkylphosphonium cations even at temperatures below 100 °C. In the case of ILs with acetate, decanoate, or dicyanamide anions, dark red to purple colored solutions form. A study combining NMR, UV‐Vis and Raman spectroscopy revealed the formation of tellurium anions (Ten)2− with chain lengths up to at least n=5, which are in dynamic equilibrium with each other. Since external influences could be excluded and no evidence of an ionic liquid reaction was found, disproportionation of the tellurium is the only possible dissolution mechanism. Although the spectroscopic detection of tellurium cations in these solutions is difficult, the coexistence of tellurium cations, such as (Te4)2+ and (Te6)4+, and tellurium anions could be proven by cyclic voltammetry and electrodeposition experiments. DFT calculations indicate that electrostatic interactions with the ions of the ILs are sufficient to stabilize both types of tellurium ions in solution.

Ionic liquids (ILs), especially task-specific ILs, are capable of dissolving various solids at moderate temperatures without the need for special reaction vessels. Direct synthesis of binary sulfides of B, Bi,...

Phosphorus halides in 1‐alkyl‐3‐methylimidazolium halide ionic liquids form complex anions. The dynamic exchange of the halides in these complexes—observed by theoretical calculations—suggests the possibility of a structural diffusion of the halide anions in the liquid. Accordingly, potential highly conducting solvents are envisioned, in which substitution reactions at molecular halides in halide ionic liquids can be exploited to increase ion mobilities. More information can be found in the Full Paper by O. Hollóczki, et al. on page 16323.

Ionic liquids (ILs) are able to activate elements that are insoluble in common solvents. Here, the synthesis of binary antimony compounds directly from elements was explored. The 12 elements Ti−Cu, Al, Ga, In, and Te, known to form binary compounds with Sb, were reacted with Sb in [P66614]Cl under inert conditions in a closed glass flask with vigorous stirring for 16 h at 200 °C. This was immediately successful in four cases and resulted in the formation of NiSb, InSb, Cu2Sb and Sb2Te3. The applied reaction temperature is several hundred degrees below the temperatures required for solvent‐free conversions. Compared to reactions based on diffusion in the solid state, reaction times are much shorter. The IL is not consumed and can be recycled. Since the reaction with Cu showed almost complete conversion, the influences of reaction time, temperature and medium were further investigated. Among the tested imidazolium ILs ([BMIm]Cl, [BMIm][OAc], [BDMIm]Cl) and phosphonium ILs ([P66614]X, X=Cl−, [DCA]−, [OAc]−, [NTf2]−), those with chloride anion yielded the best results. In a diffusion experiment, Cu2Sb formed on the copper, which indicates that antimony forms mobile species in these ILs. Supplemental crystal structure data of (As3S4)[AlCl4], which was ionothermally synthesized from As and S, are reported.