Ce travail présente l'étude de faisabilité des mesures de transmission avec des échantillons MINERVE à l'installation de temps de vol GELINA. L'idée principale était de définir des procédures pour analyser les résultats des mesures de transmission réalisées avec des échantillons cylindriques ne répondant pas à la géométrie de transmission idéale. La capacité d'extraire des résultats fiables a été démontrée sur l'exemple des échantillons MINERVE enrichis en argent. De plus, des mesures de transmission et de capture avec des disques standards d'argent naturel ont été effectuées pour améliorer les paramètres de résonance pour 107Ag et 109Ag. Les principales étapes de ce travail sont la réduction des données brutes (taux de comptage) pour produire des spectres de transmission et de rendement de capture, puis l'analyse des spectres avec le code d'analyse de forme des résonances REFIT. / This work presents the feasibility study of transmission measurements with the MINERVE samples at time-of-flight facility GELINA. The main idea was to define procedures to analyse results of transmission measurements using cylindrical samples which do not fulfil the ideal transmission geometry. Capability of extracting reliable results was demonstrated on the example of MINERVE samples enriched in silver. In addition, transmission and capture measurements with standard discs of natural silver were performed to improve the resonance parameters for 107Ag and 109Ag. The main steps in this work are the data reduction of measured count rate spectra to produce final transmission and capture yield spectra and the spectra analysis with the resonance shape analysis code REFIT.

Abstract This thesis presents computational first-principles investigations of nuclear magnetic resonance (NMR) parameters in metal-containing nanosystems. Special attention is paid to the relativistic effects observed in the vicinity of heavy elements. Small transition metal complexes are used to assess the feasibility of a quasirelativistic density functional theory (DFT) approach for calculating nuclear magnetic shielding tensors of increasingly heavy metal nuclei, followed by applications of the concept to larger systems. Nuclear magnetic shielding constants, shielding anisotropies, and chemical shifts with respect to metal ions are calculated in dimethyl and water complexes of the group-12 transition metals 67Zn, 111/113Cd, and 199/201Hg, using Hartree–Fock and DFT methods with relativistic corrections from the Breit–Pauli Perturbation Theory (BPPT). Four-component relativistic Dirac–Hartree–Fock and correlated, nonrelativistic ab initio calculations are used to benchmark the BPPT and DFT methods, respectively. The DFT/BPPT approach, combined with Monte Carlo simulations at finite temperatures, is subsequently used to calculate the chemical shift of a guest 129Xe inside a tetrahedral, iron-based cage. Complementing experiments, the encapsulation of xenon is verified, and empirically elusive details are revealed about the guest dynamics. Finally, the full shielding tensors of 31P and 195Pt and the indirect spin–spin coupling constants between the two nuclei are studied in five crystalline platinum(II) dialkyldithiophosphato complexes, concentrating on the solid-state chemical shift anisotropy and asymmetry parameters of phosphorus and platinum. The NMR parameters are calculated using DFT and the two-component zerothorder regular approximation (ZORA) for relativistic effects, combining molecular and solid-state models to incorporate indispensable contributions due to spin–orbit and crystal lattice corrections for the shielding tensors. Four-component matrix-Dirac–Kohn–Sham shielding calculations are used to benchmark the ZORA method. Qualitative, in cases nearly quantitative agreement is obtained with experiments, allowing the validation of the X-ray structures of the complexes, as well as a deeper analysis of the differences between them, including the major contributions to the NMR parameters. The results presented here demonstrate that computational NMR, a branch of relativistic quantum chemistry, is applicable and useful in studying nanoscale systems containing heavy elements, such as transition metals. Approximations are necessary to enable the treatment of large and complex targets, but sufficient accuracy is achieved for supplementing experiments with reliable and useful data that provides additional insight and analysis possibilities.

Abstract In this thesis, the classic Kurland-McGarvey theory for the nuclear magnetic resonance (NMR) chemical shift is presented in a modern framework for paramagnetic systems containing one or more unpaired electrons. First-principles computations are carried out for the NMR shielding tensors in paramagnetic transition-metal complexes. A combined ab initio/density-functional theory (DFT) approach is applied to obtain the necessary electron paramagnetic resonance (EPR) property tensors, i.e., the g-tensor, zero-field splitting tensor (D) and hyperfine coupling tensors (A). In DFT, both the generalised-gradient approximation and hybrid DFT are applied to calculate A. The complete active space self-consistent field theory (CASSCF) and N-electron valence-state perturbation theory (NEVPT2) are applied to calculate the g- and D-tensors. Scalar relativistic effects are included at the second-order Douglas-Kroll-Hess level for the g- and D-tensors and, for A, at the fully relativistic four-component matrix-Dirac-Kohn-Sham level. This methodology is applied to study ¹³C and ¹H chemical shifts and shielding anisotropies in a series of Co(II) pyrazolylborate complexes, a Cr(III) quinolyl-functionalised cyclopentadienyl complex, Ni(II) acetylacetonate complexes and various metallocenes. The results obtained from these calculations are generally in a good agreement with the experimental data, in some cases, for Ni(II) complexes, allowing to correct the experimental spectral signal assignment. CASSCF/NEVPT2 computations (especially for the D-tensor) are more accurate than DFT, which is useful for the purpose of obtaining the NMR chemical shifts. The computational results obtained are dependent on the choice of molecular geometry (experimental X-ray or computationally optimised), wavefunction used for g and D (CASSCF or NEVPT2), DFT functional for A, and the quality of the basis sets. The locally dense basis method used for the CASSCF/NEVPT2 computations is less expensive and gives equally good results for g and D as fully balanced basis sets. The scalar relativistic influences are usually small for g and D, but are large for A. Due to that, scalar relativistic effects are important for the chemical shift and shielding anisotropy, especially for carbon nuclei. These first-principles computations based on combined ab initio/DFT methodology are promising for the treatment of important electron correlation and scalar relativistic effects in the calculation of pNMR chemical shifts and shielding anisotropies. This work provides a straightforward platform for further development of pNMR shielding theory in terms of first-principles wavefunctions, as well as for applications in current problems in bio- and materials sciences, including low-temperature experiments. / Original papers The original papers are not included in the electronic version of the dissertation. Vaara, J., Rouf, S. A., & Mareš, J. (2015). Magnetic Couplings in the Chemical Shift of Paramagnetic NMR. Journal of Chemical Theory and Computation, 11(10), 4840–4849. https://doi.org/10.1021/acs.jctc.5b00656 Rouf, S. A., Mareš, J., & Vaara, J. (2015). ¹H Chemical Shifts in Paramagnetic Co(II) Pyrazolylborate Complexes: A First-Principles Study. Journal of Chemical Theory and Computation, 11(4), 1683–1691. https://doi.org/10.1021/acs.jctc.5b00193 Rouf, S. A., Jakobsen, V. B., Mareš, J., Jensen, N. D., McKenzie, C. J., Vaara, J., & Nielsen, U. G. (2017). Assignment of solid-state ¹³C and ¹H NMR spectra of paramagnetic Ni(II) acetylacetonate complexes aided by first-principles computations. Solid State Nuclear Magnetic Resonance, 87, 29–37. https://doi.org/10.1016/j.ssnmr.2017.07.003 Rouf, S. A., Mareš, J., & Vaara, J. (2017). Relativistic Approximations to Paramagnetic NMR Chemical Shift and Shielding Anisotropy in Transition Metal Systems. Journal of Chemical Theory and Computation, 13(8), 3731–3745. https://doi.org/10.1021/acs.jctc.7b00168 http://jultika.oulu.fi/Record/nbnfi-fe201801031039