Die Kristallstruktur von ?-Iridium(III)-Chlorid

Chemical Insights into the Formation of Colloidal Iridium Nanoparticles from In Situ X-ray Total Scattering: Influence of Precursors and Cations on the Reaction Pathway

Iridium nanoparticles are important catalysts for several chemical and energy conversion reactions. Studies of iridium nanoparticles have also been a key for the development of kinetic models of nanomaterial formation. However, compared to other metals such as gold or platinum, knowledge on the nature of prenucleation species and structural insights into the resultant nanoparticles are missing, especially for nanoparticles obtained from Ir_xCl_y precursors investigated here. We use in situ X-ray total scattering (TS) experiments with pair distribution function (PDF) analysis to study a simple, surfactant-free synthesis of colloidal iridium nanoparticles. The reaction is performed in methanol at 50 °C with only a base and an iridium salt as precursor. From different precursor salts─IrCl₃, IrCl₄, H₂IrCl₆, or Na₂IrCl₆─colloidal nanoparticles as small as Ir_∼55 are obtained as the final product. The nanoparticles do not show the bulk iridium face-centered cubic (fcc) structure but show decahedral and icosahedral structures. The formation route is highly dependent on the precursor salt used. Using IrCl₃ or IrCl₄, metallic iridium nanoparticles form rapidly from Ir_xCl_y^n- complexes, whereas using H₂IrCl₆ or Na₂IrCl₆, the iridium nanoparticle formation follows a sudden growth after an induction period and the brief appearance of a crystalline phase. With H₂IrCl₆, the formation of different Ir_n (n = 55, 55, 85, and 116) nanoparticles depends on the nature of the cation in the base (LiOH, NaOH, KOH, or CsOH, respectively) and larger particles are obtained with larger cations. As the particles grow, the nanoparticle structure changes from partly icosahedral to decahedral. The results show that the synthesis of iridium nanoparticles from Ir_xCl_y is a valuable iridium nanoparticle model system, which can provide new compositional and structural insights into iridium nanoparticle formation and growth.

Synthetic and coordination chemistry of the heavier trivalent technetium binary halides: uncovering technetium triiodide

Technetium tribromide and triiodide were obtained from the reaction of the quadruply Tc-Tc-bonded dimer Tc2(O2CCH3)4Cl2 with flowing HX(g) (X = Br, I) at elevated temperatures. At 150 and 300 °C, the reaction with HBr(g) yields TcBr3 crystallizing with the TiI3 structure type. The analogous reactions with flowing HI(g) yield TcI3, the first technetium binary iodide to be reported. Powder X-ray diffraction (PXRD) measurements show the compound to be amorphous at 150 °C and semicrystalline at 300 °C. X-ray absorption fine structure spectroscopy indicates TcI3 to consist of face-sharing TcI6 octahedra. Reactions of technetium metal with elemental iodine in a sealed Pyrex ampules in the temperature range 250-400 °C were performed. At 250 °C, no reaction occurred, while the reaction at 400 °C yielded a product whose PXRD pattern matches the one of TcI3 obtained from the reaction of Tc2(O2CCH3)4Cl2 and flowing HI(g). The thermal stability of TcBr3 and TcI3 was investigated in Pyrex and/or quartz ampules at 450 °C under vacuum. Technetium tribromide decomposes to Na{[Tc6Br12]2Br} in a Pyrex ampule and to technetium metal in a quartz ampule; technetium triiodide decomposes to technetium metal in a Pyrex ampule.