Experimental electron-density studies based on high-resolution diffraction experiments allow halogen bonds between heavy halogens to be classified. The topological properties of the electron density in Cl...Cl contacts vary smoothly as a function of the interaction distance. The situation is less straightforward for halogen bonds between iodine and small electronegative nucleophiles, such as nitrogen or oxygen, where the electron density in the bond critical point does not simply increase for shorter distances. The number of successful charge–density studies involving iodine is small, but at least individual examples for three cases have been observed. (a) Very short halogen bonds between electron-rich nucleophiles and heavy halogen atoms resemble three-centre–four-electron bonds, with a rather symmetric heavy halogen and without an appreciable σ hole. (b) For a narrow intermediate range of halogen bonds, the asymmetric electronic situation for the heavy halogen with a pronounced σ hole leads to rather low electron density in the (3,−1) critical point of the halogen bond; the properties of this bond critical point cannot fully describe the nature of the associated interaction. (c) For longer and presumably weaker contacts, the electron density in the halogen bond critical point is only to a minor extent reduced by the presence of the σ hole and hence may be higher than in the aforementioned case. In addition to the electron density and its derived properties, the halogen–carbon bond distance opposite to the σ hole and the Raman frequency for the associated vibration emerge as alternative criteria to gauge the halogen-bond strength. We find exceptionally long C—I distances for tetrafluorodiiodobenzene molecules in cocrystals with short halogen bonds and a significant red shift for their Raman vibrations.

Efficient electrochemical energy storage and conversion require high performance electrodes, electrolyte or catalyst materials. In this contribution we discuss the simulation-based effort made by Institute of Energy and Climate Research at Forschungszentrum Jülich (IEK-13) and partner institutions aimed at improvement of computational methodologies and providing molecular level understanding of energy materials. We focus on discussing correct computation of electronic structure, oxidation states and related redox reactions, phase transformation in doped oxides and challenges in computation of surface chemical reactions on oxides and metal surfaces in presence of electrolyte. Particularly, in the scope of this contribution we present new simulated data on Ni/Co and Am/U-bearing oxides, and Pb, Au and Ag metal surface materials. The computed results are combined with the available experimental data for thoughtful analysis of the computational methods performance.

The International Atomic Energy Agency implements safeguard measures to verify the compliance of Member States to their international legal obligations using nuclear material and technology only for peaceful purposes. These safeguard measures, i.a., include analytical measurements of individual micrometer- and submicrometer particles taken by the IAEA on swipe samples during safeguard inspections at nuclear facilities. To ensure the quality control of the analytical results from particle analysis and to further develop mass spectrometric analysis methods, microparticles with well-defined properties as microparticulate reference materials are required. Therefore, mixed lanthanide/uranium oxide microparticles were produced as a first step towards composite reference materials with small amounts of fission products, Pu or Th. A deep understanding of the incorporation mechanisms of dopants into U3O8 structure is essential in this regard. Therefore, bulk-scale comparison materials were produced and doped with lanthanides by co-precipitation methods and systematically investigated by TG, XRD, and Raman. These results will be integrated into the particle production process to design well-defined microparticulate mixed-oxide reference materials. Graphical abstract

The analysis of individual micrometre- and submicrometre-sized particles collected by IAEA’s safeguards inspectors on swipe samples during in-field verification activities requires the implementation of a sustainable quality control system such as suitable microparticulate reference materials. To this end, pure and neodymium-doped uranium oxide-based microparticles utilising an aerosol-based particle production process were prepared. SEM/EDX measurements confirmed the monodispersity of the produced microspheres as well as the incorporation of 15 mol% Nd into the compound particles. The timeline of structural investigations mirror the ongoing alteration of particles being stored under laboratory atmosphere. While results from in-SEM Raman (CEA, DAM) on microparticles after two years storage time point to the formation of U3O8 and a minor fraction of schoepite phase (hydrated UO3), in U L3-edge XAFS after four months storage time and U M4-edge HR-XANES after ten months storage time spectra (INE-Beamline and ACT station @ KIT synchrotron radiation source) mainly U(IV) and U(V), respectively, was observed. These results provide new insight into ageing mechanism of the microparticles after preparation. From these results important conclusions with respect to storage conditions and shelf life of the reference particles can be drawn. The first batch of pure U-oxide microparticles produced in Juelich was successfully certified regarding the isotopic composition and the U amount per particle and applied in an international laboratory exercise NUSIMEP-9. Graphic Abstract

Microparticulate reference materials with well-defined properties are needed by the International Atomic Energy Agency (IAEA) to consolidate a sustainable quality control system for analytical measurements for particle analysis in nuclear safeguards. In order to further develop analytical methods and quality control of the analytical results from particle analysis to detect even traces of dopants, such as fission products, the microparticulate reference materials must be refined according to the IAEA’s requirements. Due to yield limitations of the microparticles, a co-precipitation method was adapted to synthesize bulk-scale comparison materials doped with lanthanides to unravel the incorporation mechanism of those dopants into the uranium oxide structure in depth. Through TG-DSC studies, the temperature range of phase transitions from UO3 to U3O8 was identified and analyzed in more detail by additional systematic structural investigations of long- and short-range order phenomena with XRD and Raman, and IR, respectively. Graphical abstract