Metal Assisted Synthesis of Cationic Sulfidobismuth Cubanes in Ionic Liquids.

Invited for this month's cover is the group of Michael Ruck at the Technische Universität Dresden (Germany). The cover picture shows the spiro-dicubane Bi7 S8 5+ in the center, accompanied by two Bi4 S4 4+ hetero-cubanes on both sides, which are shown along their threefold axis. These sulfidobismuth polycations were isolated in salts with [AlCl4 ]- and [S(AlCl3 )3 ]2- anions. The starting material was Bi2 S3 , which is generally hard to dissolve but can easily be activated under ionothermal conditions. Moreover, the presence of noble metal ions, such as Ag+ , Au+ or Pt2+ , played a crucial role for the formation of those compounds. This research was performed in the framework of the Priority Program SPP 1708 "Material Synthesis Near Room Temperature" of the German Research Council (DFG). Read the full text of their Full Paper at 10.1002/open.202000246.

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.

Freestanding Nanolayers of a Wide-Gap Topological Insulator through Liquid-Phase Exfoliation.

The layered salt Bi14 Rh3 I9 is a weak three-dimensional (3D) topological insulator (TI), that is, a stack of two-dimensional (2D) TIs. It has a wide non-trivial band gap of 210 meV, which is generated by strong spin-orbit coupling, and possesses protected electronic edge-states. In the structure, charged layers of ∞ 2 [ (Bi4 Rh)3 I]2+ honeycombs and ∞ 1 [ Bi2 I8 ]2- chains alternate. The non-trivial topology of Bi14 Rh3 I9 is an inherent property of the 2D intermetallic fragment. Here, the exfoliation of Bi14 Rh3 I9 was performed using two different chemical approaches: (a) through a reaction with n-butyllithium and poly(vinylpyrrolidone), (b) through a reaction with betaine in dimethylformamide at 55 °C. The former yielded few-layer sheets of the new compound Bi12 Rh3 I, while the latter led to crystalline sheets of Bi14 Rh3 I9 with a thickness down to 5 nm and edge-lengths up to several ten microns. X-ray diffraction and electron microscopy proved that the structure of Bi14 Rh3 I9 remained intact. Thus, it was assumed that the particles are still TIs. Dispersions of these flakes now allow for next steps towards the envisioned applications in nanoelectronics, such as the study of quantum coherence in deposited films, the combination with superconducting particles or films for the generation of Majorana fermions, or studies on their behavior under the influence of magnetic or electric fields or in contact with various materials occurring in devices. The method presented generally allows to exfoliate layers with high specific charges and thus the use of layered starting materials beyond van der Waals crystals.

The Weak 3D Topological Insulator Bi12 Rh3 Sn3 I9.

Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi12 Rh3 Sn3 I9 , which is structurally closely related to Bi14 Rh3 I9 - a stable, layered material. In fact, Bi14 Rh3 I9 is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of ∞ 2 [(Bi4 Rh)3 I]2+ with topologically protected electronic edge-states. The fundamental difference between Bi14 Rh3 I9 and Bi12 Rh3 Sn3 I9 lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi14 Rh3 I9 are isolated by ∞ 1 [Bi2 I8 ]2- chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to ∞ 2 [Sn3 I8 ]2- layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity.

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 (Cu3-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 (Pred) 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 Cu3-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 Cu3-xP. Therefore, the nature of the anions present in the IL also seems to be relevant for the convenient phosphidization reaction.