[en] The following work is divided into three topics, in which 71 new coordination compounds and 11 new organic compounds are presented. The first project describes the continuation of the investigation of the versatile biquinoxen system, where biquinoxens are similar to the well-known viologens. The biquinoxen system exhibits multifaceted properties such as reversible redox states, luminescence and coordination to metal centres. In this work, the possibility of tuning the emission wavelength of the biquinoxen derivatives was investigated and in the course of this, 7 new compounds with emission wavelengths over a range of 63 nm, from green-yellow to red light, were produced. In addition, the biquinoxen system was used in reactions with transition metal salts. This involves the in-situ generation of a radical ligand species that is stabilised by coordination to Co${}^{II}$, Cu${}^{II}$ and Zn${}^{II}$ ions. The Co${}^{II}$ complexes were already described in my bachelor thesis, but were reproduced here and their supramolecular networks investigated in more detail and compared with the 4 new Cu${}^{II}$ and Zn${}^{II}$ containing complexes. The chapter on the second project describes the exploration of the complexation properties of the H${}_2$opch ((2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide) ligand family with lanthanide ions. Firstly, the influence of the different ionic radii of the lanthanides, resulting from the lanthanide contraction, was investigated in reactions with different lanthanide nitrates but with identical reaction conditions. This led to 11 new tetra- to octa-nuclear complexes. Amongst others, a mixed-valent Ce${}_4$ complex and a Gd${}_8$ compound which shows an excellent magnetocaloric effect could be isolated. Furthermore, the ligand was modified to investigate the influence of intra- and especially intermolecular interactions. The focus here was to investigate the effect of halogen interactions which have the advantage of being easily varied in strength, on the resulting optical and magnetic properties. This led to 18 new complexes. The third project deals with the expansion of a radical-lanthanide dimer system which has been under study for several years in the Powell group. Here, the already known complexes were reproduced and their properties in solution investigated. Furthermore, the magnetic properties of previously unexplored lanthanide variations were measured. All four components of the original complex (lanthanide ion, neutral co-ligand, anionic co-ligand and radical ligand) were systematically varied and magnetic measurements performed on the Dy${}^{III}$ analogues. In this investigation, 38 new complexes were prepared, amongst which one compound was identified exhibiting slow relaxation of magnetisation up to a temperature of 30 K and a thermal energy barrier of 475 K. In this systematically varied series of single molecule magnets the relaxation dynamics were investigated and compared in order to establish a strategy on how to improve the single molecule magnetic behaviour of these compounds, in particular by suppressing phonon-based relaxation processes.

[en] Electromagnetic properties and nuclear reactions in light nuclei are investigated in different low-energy ranges applying effective field theories. In particular, two topics with distinct degrees of freedom are considered: one-neutron halo nuclei in the Halo effective field theory (Halo EFT) and threshold neutral pion photoproduction employing chiral effective field theory ($\mathrm{\chi <!--\; ??\; -->}$EFT). In Halo EFT, the relevant degrees of freedom are the shallowly bound halo neutron and the tightly bound core nucleus. We extend the Halo EFT approach to shallow D-wave bound states, where the strong interaction between the core and the halo neutron is parametrized by contact interactions. We develop a power-counting scenario for arbitrary partial wave bound states and discuss its implications for universality. Furthermore, the results for electromagnetic form factors, electromagnetic transitions, and neutron capture reactions in weakly-bound D-wave states are presented of which we derive several universal correlations between electric observables. We apply our results to the two carbon isotopes ${}^{15}$C and ${}^{17}$C, that both have shallow bound states with a neutron in a D-wave relative to the core. Together with ab initio results from the no-core shell model (NCSM) and experimental data for the neutron separation energies, we obtain predictions for several electric observables in ${}^{15}$C at leading order (LO), i.e. the quadrupole and hexadecupole moments and radii as well as E1 neutron capture cross sections, using the experimentally measured E2 transition strength in ${}^{15}$C. The effects of next-toleading order corrections for our results are also addressed. We find that additional counterterms, which are required for the absorption of divergences, become more dominant in higher partial wave bound states, especially in the magnetic sector. Hence, we discuss the consequences for universality in such weakly-bound states. Threshold neutral pion photoproduction off light nuclei is investigated in chiral perturbation theory (ChPT) at LO in the chiral expansion. We calculate the expectation value of the pion production operator with nuclear wave functions obtained by the NCSM and apply a density matrix approach for the evaluation of the appropriate pion production amplitudes. At LO, one-nucleon and two-nucleon effects contribute to the amplitude. We compare our results for ${}^2$H, ${}^3$H, and ${}^3$He with the literature and find that we agree on both the one-nucleon contribution and the two-nucleon contribution, with the latter dominating at this order. The total amplitude is furthermore compared to experimental data of ${}^2$H which reveals that the experimental result is about 11% larger than our prediction. Moreover, we predict the threshold neutral pion photoproduction amplitude for ${}^6$Li in ChPT for the first time.

[en] We exploit the separation of scales in weakly-bound nuclei to compute E2 transitions and electric radii in a Halo EFT framework. The relevant degrees of freedom are the core and the halo neutron. The EFT expansion is carried out in powers of R_core/R_halo, where R_core and R_halo denote the core and halo radius, respectively. We include the strong s-wave and d-wave interactions by introducing dimer fields. The dimer propagators are regulated by employing the power-law divergence subtraction scheme and matched to the effective-range expansion in the respective channel. Electromagnetic interactions are included via minimal substitution in the Lagrangian. We demonstrate that, depending on the observable and respective partial wave, additional local gauge-invariant operators contribute in LO, NLO and higher orders. We present the modifications needed for the extension of our work to higher partial-wave bound states and discuss the consequences for universality in such systems.

[en] The no-core shell model (NCSM) and valence-space shell model (SM) are successful tools for the description of the nuclear spectroscopy. Both methods are computationally demanding and are limited by the model-space dimensions. To extend the NCSM and SM to larger model spaces, we apply an importance-truncation (IT) scheme based on a perturbative importance measure reducing the model spaces to the relevant basis states for the description of one or a few target eigenstates. This IT scheme necessitates an extrapolation to vanishing importance measure. Since the dependence of the energies on the importance measure can be highly non-linear, the extrapolation can give rise to large uncertainties. We present a more sophisticated extrapolation technique based on the energy variance, which vanishes in the limit of the full model space. We demonstrate the efficiency of the IT-NCSM and IT-SM with energy-variance extrapolation for ground-state and excitation energies of p-shell nuclei (IT-NCSM) and pf-shell nuclei (IT-SM) by comparing the results to both, full and importance-truncated NCSM and SM calculations with the conventional threshold extrapolation.

[en] When decommissioning nuclear facilities, its highly reinforced concrete buildings will be decontaminated in such a manner that most its total mass can be returned to the recycling cycle. To achieve maximum results, selective removal methods are required to reduce the radioactive waste for final storage. There are already several tools and processes for the removal of concrete surfaces available. However, these methods reach their limits when faced with in-depth contamination, e. g. in concrete cracks or in material compounds with metal anchor plates and bolts, rails, etc. A common problem is the targeted in-depth removal of reinforced concrete in cracks, openings, or installations, to a degree that the resulting surfaces are ready for release measurements. This requirement provides the central research issue of the project DefAhs (selective removal of highly reinforced concrete structures) which is now a joint project of Herrenknecht AG, Kraftanlagen Heidelberg GmbH, Leibniz University Hannover and Karlsruhe Institute of Technology. This project is being sponsored by FORKA (research in the field of decommissioning nuclear facilities) of Germany's Federal Ministry of Education and Research.

[en] We exploit the separation of scales in weakly-bound nuclei to compute E2 transitions and electric form factors in a halo effective field theory (EFT) framework. The relevant degrees of freedom are the core and the halo neutron. The EFT expansion is carried out in powers of R_c_o_r_e/R_h_a_l_o, where R_c_o_r_e and R_h_a_l_o denote the length scales of the core and halo, respectively. We include the strong s-wave and d-wave interactions by introducing dimer fields. The dimer propagators are regulated by employing the power divergence subtraction scheme and matched to the effective range expansion in the respective channel. Electromagnetic interactions are included via minimal substitution in the Lagrangian. We demonstrate that, depending on the observable and respective partial wave, additional local gauge-invariant operators contribute in LO, NLO and higher orders. (author)

[en] This report attempts to draw the first fiscal lessons from a crisis that has not yet come to an end. The Covid-19 pandemic, which broke out in China at the end of 2019 before spreading to the rest of the world, continues to take its toll on economies and societies. Although it is on its way out, this crisis will leave deep marks on the global economy. Firstly, the scale of the budgetary efforts made to cushion the effects has led to an unprecedented increase in public debt. In addition, the disorganisation of production resulting from the pandemic has led to supply shortages, which have severely constrained supply in certain sectors (electronics, automotive, etc.), contributing to the resurgence of inflation. Lastly, the crisis has accelerated economic and societal changes, some of which had been under way for several years but were not yet very visible: a turning point in the awareness of environmental challenges, the rise of remote work and the return of concerns about the location of productive activities, particularly when they contribute to establishing or regaining economic sovereignty. In this context, tax policy, without being exclusive of other instruments such as public expenditure or regulation, will play a decisive role in the years to come. In this report, the Council of Mandatory Contributions (Conseil des prelevements obligatoires - CPO) has chosen to focus on three challenges that it considers crucial in the context of exiting the crisis: social and territorial inequalities, innovation and environment. The common thread among the three subjects selected by the CPO is that they are directly in the field of action of fiscal policies: taxation is a key instrument of redistribution, whether in terms of income or wealth; innovation is the subject of numerous tax incentives, the most important of which is the research tax credit, a tax expenditure whose burden to the central government budget amounts to over Euros 6 bn, nearly twice the budget of the National Centre for Scientific Research (CNRS); lastly, taxation is at the heart of policies aimed at limiting climate change, by implementing a system of incentives designed to limit carbon emissions and encourage the use of alternative energy sources