Martin Jansen

Raman spectra of Rb4O6 and Cs4O6 were recorded at ambient temperature and hydrostatic pressures (diamond anvil cell) of up to to 63.5 GPa and 49.3 GPa, respectively. The Raman lines confirm presence of peroxide and superoxide in the mixed-valent oxides. They persist up to the highest pressures applied, indicating that both dioxide anions remain stable under these experimental conditions. Accordingly, the alkali metal sesquioxides Rb4O6 and Cs4O6 represent Type I mixed-valency according to the Robin and Day classification.

We reacted ClO ₂ and KO ₃ in liquid ammonia and expected the radical coupling to form the compound [ClO ₂ ···O ₃ ] ^– . We noted the disappearance of the characteristic red color of the ozonide solution as a clear indication that a reaction took place. Over time, colorless crystals grew, which were unambiguously identified as [NH ₄ ][ClO ₂ ] by single‐crystal X‐ray diffraction. This finding has thus provided compelling evidence that, instead of the targeted radical coupling, a one‐electron transfer comprising oxidation of [O ₃ ] ⁻ had occurred. It further demonstrates that the reduction potential of chlorine dioxide is higher than that of ozone in liquid anhydrous ammonia.

The highly reactive ozonide anion could be stabilized for the first time with a ferrocene‐based cation resulting in the title compound [CpFeCpCH₂NMe₃]O₃·1.47 NH₃. The target compound was thoroughly characterized by X‐ray diffraction [P2₁/c a = 1778.33(8) pm, b = 811.70(4) pm, c = 1111.71(5) pm, β = 91.715(2)°, R = 0.0325, 40301 reflections]. Additionally, infrared spectroscopy as well as quantum chemical calculations of the embedded anion were carried out to further characterize the compound and investigated the OO bond lengths and OOO bond angles of the ozonide anion.

Pyrrolidinium‐based cations were systematically modified to investigate their influence on ozonide and superoxide anions and to understand the scattering of experimentally determined dimensions of these radical anions. Hence, 1‐ethyl‐1‐methyl‐pyrrolidinium, 1‐propyl‐1‐methyl‐pyrrolidinium and 1‐butyl‐1‐methyl‐pyrrolidinium superoxide, as well as 1‐methyl‐1‐methyl‐pyrrolidinium and 1‐propyl‐1‐methyl‐pyrrolidinium ozonide have been synthesized via ion exchange in liquid ammonia, and characterized by single‐crystal X‐ray diffraction. Attempts to crystallize the 1‐ethyl‐1‐methyl‐pyrrolidinium and 1‐butyl‐1‐methyl‐pyrrolidinium ozonide in the same way failed. Two fundamental causes for the variation in the dimensions of the radical anions were revealed: firstly, the reduced accuracy of the experimental data due to static disorder and increased thermal motion, and secondly, the effects of the environments to which the anions are exposed in the crystal matrix. Quantum‐chemical calculations of the isolated or embedded anions were also performed, showing a significant influence of hydrogen bonding and crystal field effects.

We report on an unexpected reaction between ammonia and potassium ozonide dissolved in liq. NH₃ resulting in the formation of peroxynitrite, [ONOO]⁻, which exclusively happens in the presence of a specific partially fluorinated aniline‐based ammonium cation. High‐resolution structural data of the peroxynitrite anion in cis‐conformation have been obtained. We further studied this molecule anion by single crystal Raman spectroscopy. The cis and trans isomers of peroxynitrite were analysed computationally with respect to their relative energies, the cis‐trans transition barrier and their decomposition pathways to the nitrate anion. By experimentally examining cations decorated with fluorine ligands to different degrees, we demonstrate that fluorine specific interactions play a crucial role in the unexpected formation of peroxynitrite and as a conspicuously structure directing factor for the underlying crystalline solid phases, exhibiting distinct micro‐separations of fluorine and hydrogen enriched regions.

The compounds [Me ₃ N(C ₆ H ₃ (CF ₃ ) ₂ )][BF ₄ ] and [Me ₃ N(C ₆ H ₃ (CH ₃ ) ₂ )][BF ₄ ] were synthesized from commercially available starting materials and fully characterized by single-crystal X-ray diffraction, NMR, IR and Raman spectroscopy, as well as mass spectrometry. Both ammonium cations show potential for applications in crystal engineering due to their structure directing properties in the solid state.

The B‐site ordered double perovskite Sr₂CaOsO₆ has been synthesized by a solid‐state reaction under ambient pressure. Sr₂CaOsO₆ is isostructural to Sr₂NaOsO₆ and Sr₂CaReO₆, thus crystallizes in the monoclinic space group P2₁/n, in contrast to cubic lattice symmetry reported in an earlier publication. The compound remains paramagnetic down to a temperature of 2 K. This finding is of relevance with regard to the high‐temperature ferromagnetism observed in Sr₃OsO₆ thin films and may find interest in view of possible exotic ground states in frustrated magnetic systems.