Synthesis of Sb2Se3and Bi2Se3Nanoparticles in Ionic Liquids at Low Temperatures and Solid State Structure of [C4C1Im]3[BiCl6]

Ultra-mild synthesis of nanometric metal chalcogenides using organyl chalcogenide precursors

Bis(trialkylsilyl) monochalcogenides and diorganyl dichalcogenides, (R₃Si)₂E and R₂E₂ (E = S, Se or Te and R = alkyl, aryl or allyl group), have emerged in the past decade as excellent reagents for the synthesis of metal chalcogenide nanoparticles (NPs) and clusters owing to their ability to transfer the chalcogenide anion (E^2-) under ultra-mild conditions and versatility in reacting even with non-conventional metal reagents or being employed in a variety of synthetic methods. In comparison, the related non-silylated diorganyl monochalcogenides R₂E have received attention only recently for the solution phase synthesis of metal chalcogenide NPs. In spite of sharing many similarities, these three families of organyl chalcogenides are different in their coordination ability and decomposition behavior, and therefore in reactivities towards metal reagents. This feature article provides a concise overview on the use of these three families as synthons for the ultralow-temperature synthesis of metal chalcogenide nanomaterials, deliberating their different decomposition mechanisms and critically assessing their advantages for certain applications. More specifically, it discusses their usefulness in (i) affording molecular precursors with different kinetic and thermal stabilities, (ii) isolating reactive intermediates for comprehending the mechanism of molecule-to-nanoparticle transformation and, therefore, achieving fine control over the synthesis, (iii) stabilizing isolable metastable or difficult-to-achieve phases, and (iv) yielding complex ternary nanoparticles with controlled stoichiometry or composites with sensitive materials without modifying the characteristics of the latter. Besides providing a perspective on the low-temperature synthesis of nanomaterials, this overview is expected to assist further progress, particularly in the field of R₂E, leading to interesting materials including metastable ones for new applications.

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.

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.

Influence of Nanoparticle Processing on the Thermoelectric Properties of (Bix Sb1-X )2 Te3 Ternary Alloys

The synthesis of phase-pure ternary solutions of tetradymite-type materials (Bix Sb1-x )2 Te3 (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties - Seebeck coefficient as well as electrical and thermal conductivity - is demonstrated.

Thermodynamic properties of selenoether-functionalized ionic liquids and their use for the synthesis of zinc selenide nanoparticles

Three selenoether-functionalized ionic liquids (ILs) of N-[(phenylseleno)methylene]pyridinium (1), N-(methyl)- (2) and N-(butyl)-N'-[(phenylseleno)methylene]imidazolium (3) with bis(trifluoromethanesulfonyl)imide anions ([NTf2]) were prepared from pyridine, N-methylimidazole and N-butylimidazole with in situ obtained phenylselenomethyl chloride, followed by ion exchange to give the desired compounds. The crystal structures of the bromide and tetraphenylborate salts of the above cations (1-Br, 2-BPh4 and 3-BPh4) confirm the formation of the desired cations and indicate a multitude of different supramolecular interactions besides the dominating Coulomb interactions between the cations and anions. The vaporization enthalpies of the synthesized [NTf2]-containing ILs were determined by means of a quartz-crystal microbalance method (QCM) and their densities were measured with an oscillating U-tube. These thermodynamic data have been used to develop a method for assessment of miscibility of conventional solvents in the selenium-containing ILs by using Hildebrandt solubility parameters, as well as for modeling with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) method. Furthermore, structure-property relations between selenoether-functionalized and similarly shaped corresponding aryl-substituted imidazolium- and pyridinium-based ILs were analyzed and showed that the contribution of the selenium moiety to the enthalpy of vaporization of an IL is equal to the contribution of a methylene (CH2) group. An incremental approach to predict vaporization enthalpies of ILs by a group contribution method has been developed. The reaction of these ILs with zinc acetate dihydrate under microwave irradiation led to ZnSe nanoparticles of an average diameter between 4 and 10 nm, depending on the reaction conditions.

Improving the zT value of thermoelectrics by nanostructuring: tuning the nanoparticle morphology of Sb2Te3by using ionic liquids

Morphology and thermoelectric properties of Sb₂Te₃nanoparticles synthesized in ionic liquids are controlled by the cation and anion.