Synthese kristalliner Chalkogenide in ionischen Flüssigkeiten

Exploration of metal sulfide syntheses and the dissolution process of antimony sulfide in phosphonium-based ionic liquids

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, Ge, Mo, Cu, Au, Sn, In, Ti, V, Fe, Co, Ga, Ni, Al, Zn, and Sb in [P₆₆₆₁₄]Cl was tested at 100 °C, i.e. below the melting point of sulfur. Under these conditions, substantial sulfide formation occurred only for nickel (Ni₃S₄, Ni₃S₂, NiS) and copper (Cu₂S, CuS). Sb showed no formation of crystalline sulfide, but after addition of EtOH, an orange material precipitated which was identified as amorphous metastibnite. Subsequently, the dissolution of antimony sulfide (Sb₂S₃), the main source of antimony production, in the phosphonium-based ILs [P₆₆₆₁₄][OAc] and [P₆₆₆₁₄]Cl at 100 °C was studied in detail. The dissolution proceeds without H₂S evolution, and amorphous Sb₂S₃ can be precipitated from these solutions. Heating Sb₂S₃ in the Lewis-acidic IL [BMIm]Cl·4.7AlCl₃ led to the crystallization of [Sb₁₃S₁₆Cl₂][AlCl₄]₅, which contains a new quadruple heterocubane cation.

Ionothermal Synthesis of Sulfidobismuth spiro-Dicubane Cations

Bi2 S3 was dissolved in the presence of NaCl in the ionic liquid [BMIm]Cl ⋅ 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(Bi7 S8 )[S(AlCl3 )3 ]2 [AlCl4 ]2 (1) precipitated. X-ray diffraction on single-crystals of 1 revealed a triclinic crystal structure that contains (Bi7 S8 )5+ spiro-dicubanes, [S(AlCl3 )3 ]2- tetrahedra triples, isolated [AlCl4 ]- tetrahedra, and sodium cations.

Inorganic Synthesis Based on Reactions of Ionic Liquids and Deep Eutectic Solvents

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.

Metal Assisted Synthesis of Cationic Sulfidobismuth Cubanes in Ionic Liquids

Bi2 S3 was dissolved in the presence of either AuCl/PtCl2 or AgCl in the ionic liquids [BMIm]Cl ⋅ xAlCl3 (BMIm=1-n-butyl-3-methylimidazolium; x=4-4.3) through annealing the mixtures at 180 or 200 °C. Upon cooling to room temperature, orange, air-sensitive crystals of [BMIm](Bi4 S4 )[AlCl4 ]5 (1) or Ag(Bi7 S8 )[S(AlCl3 )3 ]2 [AlCl4 ]2 (2) precipitated, respectively. 1 did not form in the absence of AuCl/PtCl2 , suggesting an essential role of the metal cations. X-ray diffraction on single-crystals of 1 revealed a monoclinic crystal structure that contains (Bi4 S4 )4+ heterocubanes and [AlCl4 ]- tetrahedra as well as [BMIm]+ cations. The intercalation of the ionic liquid was confirmed via solid state NMR spectroscopy, revealing unusual coupling behavior. The crystal structure of 2 consists of (Bi7 S8 )5+ spiro-dicubanes, [S(AlCl3 )3 ]2- tetrahedra triples, isolated [AlCl4 ]- tetrahedra, and heavily disordered silver(I) cations. No cation ordering took place in 2 upon slow cooling to 100 K.

Heavy Chalcogenide-Based Ionic Liquids in Syntheses of Metal Chalcogenide Materials near Room Temperature

This minireview describes two strategically different and unexplored approaches to use ionic liquids (IL) containing weakly solvated and highly reactive chalcogenide anions [E-SiMe3 ]- and [E-H]- of the heavy chalcogens (E=S, Se, Te) in materials synthesis near room temperature. The first strategy involves the synthesis of unprecedented trimethylsilyl chalcogenido metalates Cat+ [M(E-SiMe3 )n ]- (Cat=organic IL cation) of main group and transition metals (M=Ga, In, Sn, Zn, Cu, Ag, Au). These fully characterized homoleptic metalates serve as thermally metastable precursors in low-temperature syntheses of binary, ternary and even quaternary chalcogenide materials such as CIGS and CZTS relevant for semiconductor and photovoltaics (PV) applications. Furthermore, thermally and protolytically metastable coinage metalates Cat+ [M(ESiMe3 )2 ]- (M=Cu, Ag, Au; E=S, Se) are accessible. Finally, the use of precursors BMPyr[E-SiMe3 ] (E=Se,Te; BMPyr=1-butyl-1-methylpyrrolidinium) as sources of activated selenium and tellurium in the synthesis of high-grade thermoelectric nanoparticles Bi2 Se3 and Bi2 Te3 is shortly highlighted. The second synthesis strategy involves the metalation of ionic liquids Cat[S-H] and Cat[Se-H] by protolytically highly active metal alkyls or amides Rn M. This rather general approach towards unknown chalcogenido metalates Catm [Rn-1 M(E)]m (E=S, Se) will be demonstrated in a research paper following this short review head-to-tail.

Pseudohalogen Chemistry in Ionic Liquids with Non-innocent Cations and Anions

Within the second funding period of the SPP 1708 "Material Synthesis near Room Temperature",which started in 2017, we were able to synthesize novel anionic species utilizing Ionic Liquids (ILs) both, as reaction media and reactant. ILs, bearing the decomposable and non-innocent methyl carbonate anion [CO3 Me]- , served as starting material and enabled facile access to pseudohalide salts by reaction with Me3 Si-X (X=CN, N3 , OCN, SCN). Starting with the synthesized Room temperature Ionic Liquid (RT-IL) [nBu3 MeN][B(OMe)3 (CN)], we were able to crystallize the double salt [nBu3 MeN]2 [B(OMe)3 (CN)](CN). Furthermore, we studied the reaction of [WCC]SCN and [WCC]CN (WCC=weakly coordinating cation) with their corresponding protic acids HX (X=SCN, CN), which resulted in formation of [H(NCS)2 ]- and the temperature labile solvate anions [CN(HCN)n ]- (n=2, 3). In addition, the highly labile anionic HCN solvates were obtained from [PPN]X ([PPN]=μ-nitridobis(triphenylphosphonium), X=N3 , OCN, SCN and OCP) and HCN. Crystals of [PPN][X(HCN)3 ] (X=N3 , OCN) and [PPN][SCN(HCN)2 ] were obtained when the crystallization was carried out at low temperatures. Interestingly, reaction of [PPN]OCP with HCN was noticed, which led to the formation of [P(CN)2 ]- , crystallizing as HCN disolvate [PPN][P(CN⋅HCN)2 ]. Furthermore, we were able to isolate the novel cyanido(halido) silicate dianions of the type [SiCl0.78 (CN)5.22 ]2- and [SiF(CN)5 ]2- and the hexa-substituted [Si(CN)6 ]2- by temperature controlled halide/cyanide exchange reactions. By facile neutralization reactions with the non-innocent cation of [Et3 HN]2 [Si(CN)6 ] with MOH (M=Li, K), Li2 [Si(CN)6 ] ⋅ 2 H2 O and K2 [Si(CN)6 ] were obtained, which form three dimensional coordination polymers. From salt metathesis processes of M2 [Si(CN)6 ] with different imidazolium bromides, we were able to isolate new imidazolium salts and the ionic liquid [BMIm]2 [Si(CN)6 ]. When reacting [Mes(nBu)Im]2 [Si(CN)6 ] with an excess of the strong Lewis acid B(C6 F5 )3 , the voluminous adduct anion {Si[CN⋅B(C6 F5 )3 ]6 }2- was obtained.

Ionic Liquid-Driven Formation of and Cation Exchange in Layered Sulfido Stannates - a CH2 Group Makes the Difference

Two types of layered sulfido stannates or a molecular cluster compound are obtained upon ionothermal treatment of the simple sulfido stannate salt K4 [SnS4 ]  ·  4H2 O that is based on binary tetrahedral [SnS4 ]4- anions. The formation of the respective products, novel compounds (C4 C1 C1 Im)2 [Sn3 S7 ] (1 a), (C4 C1 C2 Im)2 [Sn3 S7 ] (1 b), and (C4 C1 C2 Im)2 [Sn4 S9 ] (2) with layered anionic substructures, or the recently reported compound (C4 C1 C1 Im)4+x [Sn10 O4 S16 (SMe)4 ][An]x (A) comprising a molecular cluster anion, is controlled by both the choice of the ionic liquid cation and the reaction temperature. We report the scale-up of the syntheses by a factor of 100 with regard to other reported ionothermal syntheses of related compounds, and a procedure of how to isolate them in phase-pure form - both being rare observations in chalcogenido stannate chemistry in ionic liquids. Moreover, the synthesis of compound 1 a can be achieved by rapid cation exchange starting out from 1 b, which has not been reported for organic cations in any chalcogenido stannate salt to date.

Structural Expansion of Chalcogenido Tetrelates in Ionic Liquids by Incorporation of Sulfido Antimonate Units

Multinary chalcogenido (semi)metalate salts exhibit finely tunable optical properties based on the combination of metal and chalcogenide ions in their polyanionic substructure. Here, we present the structural expansion of chalcogenido germanate(IV) or stannate(IV) architectures with SbIII , which clearly affects the vibrational and optical absorption properties of the solid compounds. For the synthesis of the title compounds, [K4 (H2 O)4 ][Ge4 S10 ] or [K4 (H2 O)4 ][SnS4 ] were reacted with SbCl3 under ionothermal conditions in imidazolium-based ionic liquids. Salt metathesis at relatively low temperatures (120 °C or 150 °C) enabled the incorporation of (formally) Sb3+ ions into the anionic substructure of the precursors, and their modification to form (Cat)16 [Ge2 Sb2 S7 ]6 [GeS4 ] (1) and (Cat)6 [Sn10 O4 S20 ][Sb3 S4 ]2 (2 a and 2 b), wherein Cat=(C4 C1 C1 Im)+ (1 and 2 a) or (C4 C1 C2 Im)+ (2 b). In 1, germanium and antimony atoms are combined to form a rare noradamantane-type ternary molecular anion, six of which surround an {GeS4 } unit in a highly symmetric secondary structure, and finally crystallize in a diamond-like superstructure. In 2, supertetrahedral oxo-sulfido stannate clusters are generated, as known from the ionothermal treatment of the stannate precursor alone, yet, linked here into unprecedented one-dimensional strands with {Sb3 S4 } units as linkers. We discuss the single-crystal structures of these uncommon salts of ternary and quaternary chalcogenido (semi)metalate anions, as well as their Raman and UV-visible spectra.

Discrete Supertetrahedral T5 Selenide Clusters and Their Se/S Solid Solutions: Ionic-Liquid-Assisted Precursor Route Syntheses and Photocatalytic Properties

Although supertetrahedral Tn sulfide clusters (n=2-6) have been extensively explored, the synthesis of Tn selenide clusters with n>4 has not been achieved thus far. Reported here are ionic-liquid (IL)-assisted precursor route syntheses, characterizations, and the photocatalytic properties of six new M-In-Q (M=Cu or Cd; Q=Se or Se/S) chalcogenide compounds, namely [Bmmim]₁₂ Cu₅ In₃₀ Q₅₂ Cl₃ (Im) (Q=Se (T5-1), Se_48.5 S_3.5 (T5-2); Bmmim=1-butyl-2,3-dimethylimidazolium, Im=imidazole), [Bmmim]₁₁ Cd₆ In₂₈ Q₅₂ Cl₃ (MIm) (Q=Se (T5-3), Se_28.5 S_23.5 (T5-4), Se₁₆ S₃₆ (T5-5); MIm=1-methylimidazole), and [Bmmim]₉ Cd₆ In₂₈ Se₈ S₄₄ Cl(MIm)₃ (T5-6). The cluster compounds T5-1 and T5-3 represent the largest molecular supertetrahedral Tn selenide clusters to date. Under visible-light illumination, the Cu-In-Q compounds showed photocatalytic activity towards the decomposition of crystal violet, whereas the Cd-In-Q compounds exhibited good photocatalytic H₂ evolution activity. Interestingly, the experimental results show that the photocatalytic performances of the selenide/sulfide solid solutions were significantly better than those of their selenide analogues, for example, the degradation time of the organic dye with T5-2 was much shorter than that with T5-1, whereas the photocatalytic H₂ evolution efficiencies with T5-3-T5-6 improved significantly with increasing sulfur content. This work highlights the significance of IL-assisted precursor route synthesis and the tuning of photocatalytic properties through the formation of solid solutions.

Synthesis of nickel/gallium nanoalloys using a dual-source approach in 1-alkyl-3-methylimidazole ionic liquids

NiGa is a catalyst for the semihydrogenation of alkynes. Here we show the influence of different dispersion times before microwave-induced decomposition of the precursors on the phase purity, as well as the influence of the time of microwave-induced decomposition on the crystallinity of the NiGa nanoparticles. Microwave-induced co-decomposition of all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in the ionic liquid [BMIm][NTf2] selectively yields small intermetallic Ni/Ga nanocrystals of 5 ± 1 nm as derived from transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and supported by energy-dispersive X-ray spectrometry (EDX), selected-area energy diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). NiGa@[BMIm][NTf2] catalyze the semihydrogenation of 4-octyne to 4-octene with 100% selectivity towards (E)-4-octene over five runs, but with poor conversion values. IL-free, precipitated NiGa nanoparticles achieve conversion values of over 90% and selectivity of 100% towards alkene over three runs.

Organotin Selenide Clusters and Hybrid Capsules

Several compounds with unique structural motifs that have already been known from organotin sulfide chemistry, but remained unprecedented in organotin selenide chemistry so far, have been synthesized. The reaction of [(R¹ Sn)₄ Se₆ ] (R¹ =CMe₂ CH₂ C(O)Me) with N₂ H₄ ⋅H₂ O/(SiMe₃ )₂ Se and PhN₂ H₃ /(SiMe₃ )₂ Se led to the formation of [{(R² Sn)₂ SnSe₄ }₂ (μ-Se)₂ ] (1; R² =CMe₂ CH₂ C(Me)NNH₂ ) and [{(R³ Sn)₂ SnSe₄ }₂ (μ-Se)₂ ] (2; R³ =CMe₂ CH₂ C(Me)NNPhH)). The addition of ortho-phthalaldehyde to [(R² Sn)₄ Se₆ ] yielded a cluster with intramolecular bridging of the organic groups, namely, [(R⁴ Sn₂ )₂ Se₆ ] (3; R⁴ =(CMe₂ CH₂ C(Me)NNCH)₂ C₆ H₄ ). The introduction of organic ligands with longer chains finally allowed the isolation of inorganic-organic capsules of the type [(μ-R)₃ (Sn₃ Se₄ )₂ ]X₂ , with R=(CMe₂ CH₂ C(Me)NNHC(O))₂ (CH₂ )₄ and X=[SnC₃ ], Cl (4 a, b) or R=CMe₂ CH₂ C(Me)NNH)₂ and X=[SnCl₃ ] (5). The capsules enclose solvent molecules and/or anions as guests. All compounds were characterized by means of single-crystal X-ray diffraction studies, NMR spectroscopy, and mass spectrometry.

Multi-Valent Group 14 Chalcogenide Architectures from Ionic Liquids: 0D-{[Cs@SnII4 (GeIV4 Se10 )4 ]7- } and 2D-{[SnII (GeIV4 Se10 )]2- }

In order to explore if and how salts comprising polycations and salts comprising polyanions might interact, the [AlBr₄ ]^- salt of the [Pt@Bi₁₀ ]⁴⁺ cluster cation was added to the reaction mixture for the synthesis of the supersphere cluster anion [Ge₂₄ Sn₃₆ Se₁₃₂ ]^24- from Cs₄ [Ge₄ Se₁₀ ]⋅H₂ O and SnCl₄ ⋅5 H₂ O under ionothermal conditions at 120 °C. Indeed, the reaction yields two new compounds, depending on the cation of the used ionic liquid. Apparently, the polycation is not retained under the given conditions, but it acts as a reductant affording Sn^II . In a (C₄ C₁ C₁ im)⁺ -based ionic liquid mixture, a unique supertetrahedral anion is obtained that embeds a Cs⁺ cation, 0D-{[Cs@Sn^II₄ (Ge^IV₄ Se₁₀ )₄ ]^7- }, while (C₄ C₁ im)⁺ cations stabilize an unprecedented ternary layered anion, 2D-{[Sn^II (Ge^IV₄ Se₁₀ )]^2- }. Test reactions with common sources of Sn^II did not afford the new compounds, indicating the necessity of an in situ reduction, for which the polycation seems appropriate.

[Hg4 Te8 (Te2 )4 ]8- : A Heavy Metal Porphyrinoid Embedded in a Lamellar Structure

The use of ionic liquids (C_n C₁ Im)[BF₄ ] with long alkyl chains (n=10, 12) in the ionothermal treatment of Na₂ [HgTe₂ ] led to lamellar crystal structures with molecular macrocyclic anions [Hg₈ Te₁₆ ]^8- (1), the heaviest known topological relative of porphyrin. [Hg₈ Te₁₆ ]^8- differs from porphyrin by the absence of an electronic π-system, which prevents a "global" aromaticity. Quantum chemical studies reveal instead small ring currents in the pyrrole-type five-membered rings that indicate weak local (σ) aromaticity. As a result of their lamellar nature, the compounds are promising candidates for the formation of sheets containing chalcogenidometalate anions.

Ternary Mixed-Valence Organotin Copper Selenide Clusters

Reactions of the organotin selenide chloride clusters [(R¹ Sn^IV )₃ Se₄ Cl] (A, R¹ =CMe₂ CH₂ C(O)Me) or [(R¹ Sn^IV )₄ Se₆ ] (B) with [Cu(PPh₃ )_3-x Cl_x ] yield cluster compounds with different inorganic, mixed-valence core structures: [Cu₄ Sn^II Sn^IV₆ Se₁₂ ], [Cu₂ Sn^II₂ Sn^IV₄ Se₈ Cl₂ ], [Cu₂ Sn^II Sn^IV₄ Se₈ ], [Cu₂ Sn^II₂ Sn^IV₂ Se₄ Cl₄ ], and [Cu₂ Sn^IV₂ Se₄ ]. Five of the compounds, namely [(CuPPh₃ )₂ {(R¹ Sn^IV )₂ Se₄ }] (1), [(CuPPh₃ )₂ Sn^II {(R² Sn^IV )₂ Se₄ }₂ ] (2), [(CuPPh₃ )₂ (Sn^II Cl)₂ {(RSn^IV )₂ Se₄ }₂ ] (3) [(CuPPh₃ )₂ (Sn^II Cu₂ ){(R¹ Sn^IV )₂ Se₄ }₃ ] (4), and [Cu(CuPPh₃ )(Sn^II Cu₂ ){(R¹ Sn^IV )₂ Se₄ }₃ ] (5) are structurally closely related. They are based on [(CuPPh₃ )₂ {(RSn^IV )₂ Se₄ }_n ] aggregates comprising [(RSn^IV )₂ Se₄ ] and [CuPPh₃ ] building units, which are linked by further metal atoms. A sixth compound, [(CuPPh₃ )₂ (Sn^II Cl)₂ {(R¹ Sn^IV Cl)Se₂ }₂ ] (6), differs from the others by containing [(RSn^IV Cl)Se₂ ] units instead, which affects the absorption properties. The compounds were analyzed by single-crystal X-ray diffraction, NMR and ¹¹⁹ Sn Mössbauer spectroscopy, DFT calculations as well as optical absorption experiments.

Mechanistic exploration of the copper(i) phosphide synthesis in phosphonium-based and phosphorus-free ionic liquids

The mechanism of the synthesis of copper(i) phosphide (Cu_3-xP) in the ionic liquid (IL) trihexyl(tetradecyl)phosphonium chloride ([P₆₆₆₁₄][Cl]) was investigated. The phosphide formation is promoted by a transformation of red phosphorus (P_red) into mobile P₄ molecules and a surface activation of copper caused by the IL including the Brønsted acidic impurity. The surface activation is important to obtain a quantitative product yield. Moreover, we demonstrate that single-phase Cu_3-xP can also be synthesized in the nitrogen-based IL tetrabutylammonium chloride ([N₄₄₄₄][Cl]). Further substitution of the anion of the IL using tetrabutylammonium bromide ([N₄₄₄₄][Br]) or the complete replacement of the IL by a deep eutectic solvent consisting of adipic acid and betaine do not lead to single-phase Cu_3-xP. Therefore, the nature of the anions present in the IL also seems to be relevant for the convenient phosphidization reaction.

Exploring the Chemical Reaction Space at the Formation of Chalcogenidometalate Superspheres in Ionic Liquids

The synthesis of anionic chalcogenidometalate superspheres can be achieved from [Ge₄ Se₁₀ ]^4- salts and SnCl₄ in ionic liquids with 1-alkyl-(2,)3-(di)methylimidazolium cations, denoted as (C_n (C₁ )C₁ Im)⁺ (alkyl = butyl for n=4, hexyl for n=6, octyl for n=8). Their formation is apparently independent from the lengths of the C_n chain, and the presence or absence of a second methyl group at the ionic liquid cation (that are exchanged for alkali metal cations in precursor compounds during the reactions), although this may appear counterintuitive. In contrast, and equally counterintuitive, the ionic liquid anion was found to play a crucial role for both the general observability as well as the crystal yield and quality of the products, although they are not part of the product: a minimum content of chloride is needed, while ionic liquids with [BF₄ ]^- anions alone do not support the product formation/crystallization. The observation suggests a subtle equilibrium of SnCl₄ with according halidostannate anions that decreases the reactivity of the tin source. The finding is of particular interest, as chloride anions were shown to have been major impurities of former "chloride-free" ionic liquid charges, which potentially led to irreproducible synthesis protocols in the literature.