Sebastian Fichter

Recent synthesis and characterization of U ^IV and Np ^IV complexes [AnX(( S )-PEBA) ₃ ] and [AnX(iPr ₂ BA) ₃ ] (X = F, Cl) have revealed a characteristic inversion of paramagnetic ¹ H-NMR shifts for both [UFL ₃ ] representatives compared to the [UClL ₃ ] compounds.

Where are the heavy elements produced in the Universe? While core-collapse supernovae are confirmed sources of ⁶⁰ Fe, the origin of heavier r-process nuclei such as ²⁴⁴ Pu and ²⁴⁷ Cm remains debated. Here we used single-atom counting of live ⁶⁰ Fe, ²⁴⁴ Pu and ²⁴⁷ Cm in a deep-ocean ferromanganese crust to trace such nucleosynthesis events near Earth over millions of years. The observed non-correlation of the ²⁴⁴ Pu and ⁶⁰ Fe profiles supports a continuous r-process influx to Earth that is independent of core-collapse supernovae and constrains the core-collapse supernova r-process yield of actinide isotopes. The non-observation of ²⁴⁷ Cm, produced concurrently with ²⁴⁴ Pu, sets a time limit on the last actinide-producing r-process event near Earth of more than 90–100 Myr ago. Our measured interstellar signatures suggest the occurrence of an old and rare r-process event leading to a diffuse ²⁴⁴ Pu background inside and outside the Local Bubble.

The solar system currently traverses the Local Interstellar Cloud (LIC), one of several warm cloudlets of the Complex of Local Interstellar Clouds (CLIC) in the solar neighborhood. The origin of these cloudlets is unknown and could be related to supernova shock wave dynamics. If supernovae are the source of these cloudlets or influence their properties, the CLIC may act as a cosmic archive for the supernova-produced radionuclide Fe 60 . We detected minuscule traces of interstellar Fe 60 in 295 kg of the European Project for Ice Coring in Antarctica Dronning Maud Land ice core, covering the time period 40–81 kyr ago. We find an Fe 60 / Mn 53 ratio of ( 8 ± 5 ) × 10 − 4 , slightly above the expected cosmogenic production, corresponding to an interstellar deposition rate of ( 0.22 − 0.12 + 0.14 ) Fe 60 at / cm 2 / yr . This influx is significantly lower than that observed in recent Antarctic snow and marine sediment records during the last 40 kyr. These results suggest that the LIC is a cosmic archive for supernova-produced Fe 60 . The imprinted Fe 60 time profile is evidence for a changing local interstellar environment over the last 80 kyr.

Cosmogenic nuclide dating relies on the constancy of production and incorporation of radionuclides in geological archives. Anomalous deviations from constancy during the Holocene or Pleistocene are frequently used as global benchmarks to harmonize different data sets. A similar dating anchor on the million year timescale was so far not presented. In this work, we report on a prolonged cosmogenic ¹⁰Be anomaly during the late Miocene recorded in several Central and Northern Pacific deep-ocean ferromanganese crusts in the time period 9–11.5 Myr ago peaking at 10.1 Myr. Potential origins of this anomaly are discussed in the light of geological, climatic, solar and astrophysical events. This anomaly has the potential to be an independent time marker for marine archives.

Isostructural trivalent lanthanide and actinide amidinates bearing the N,N'-bis(isopropyl)benzamidinate (iPr₂BA) ligand [Ln^III/An^III(iPr₂BA)₃] (Ln = La, Nd, Sm, Eu, Yb, Lu; An = U, Np) have been synthesized and characterized in both solid and solution states. All compounds were examined in the solid state utilizing single crystal X-ray diffraction (SC-XRD), revealing a notable deviation in the actinide series with shortened bond lengths compared to the trend in the lanthanide series, suggesting a nonionic contribution to the actinide-ligand bonding. Quantum-chemical bonding analysis further elucidated the nature of these interactions, highlighting increased covalency within the actinide series, as evidenced by higher delocalization indices and greater 5f orbital occupation, except for Th(III) and Pa(III), which demonstrated substantial 6d orbital occupancies. An in-depth paramagnetic NMR study in solution also sheds light on the covalent character of actinide-ligand bonding, with the separation of pseudocontact (PCS) and contact shift (FCS) contributions employing the Bleaney and Reilley method. This analysis unveiled significant contact contributions in the actinide complexes, indicating enhanced covalency in actinide-ligand bonding. To corroborate these observations, an accurate PCS calculation method based on the Kuprov equation, incorporating both the distribution of electronic spin density and magnetic susceptibility obtained from CASSCF calculations, was applied and compared with experimental values.