Alexander Wolff

Controlled Synthesis of Polyions of Heavy Main-Group Elements in Ionic Liquids

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.

Resource-Efficient High-Yield Ionothermal Synthesis of Microcrystalline Cu3–xP

Polycrystalline Cu3-xP was successfully synthesized in different ionic liquids comprising imidazolium and phosphonium cations. The reaction of elemental copper and red phosphorus in trihexyltetradecylphosphonium chloride at 200 °C led to single-phase Cu3-xP (x = 0.05) within 24 h with a quantitative yield (99%). Liquid-state nuclear magnetic resonance spectroscopy of the ionic liquids revealed degeneration of the imidazolium cations under the synthesis conditions, while phosphonium cations remain stable. The solid products were characterized with X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and elemental analysis. A reinvestigation of the electronic transport properties of Cu2.95(4)P showed metallic behavior for the bulk material. The formation of CuP2 during the synthesis of phosphorus-rich Cu3-xP (x ≥ 0.1) was observed.

Multi-Valent Group 14 Chalcogenide Architectures from Ionic Liquids: 0D-{[Cs@SnII 4(GeIV 4Se10)4]7−} and 2D-{[SnII(GeIV 4Se10)]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 SnII . In a (C4 C1 C1 im)+ -based ionic liquid mixture, a unique supertetrahedral anion is obtained that embeds a Cs+ cation, 0D-{[Cs@SnII4 (GeIV4 Se10 )4 ]7- }, while (C4 C1 im)+ cations stabilize an unprecedented ternary layered anion, 2D-{[SnII (GeIV4 Se10 )]2- }. Test reactions with common sources of SnII did not afford the new compounds, indicating the necessity of an in situ reduction, for which the polycation seems appropriate.

Spontaneous Substitutions at Phosphorus Trihalides in Imidazolium Halide Ionic Liquids: Grotthuss Diffusion of Anions?

PX3 compounds (X=Cl, Br, I) in imidazolium halide ionic liquids combine with the anion Z (Z=Cl, Br, I) of the solvent to form [PX3 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 31 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.