Magnetic Resonance Properties of Actinyl Carbonate Complexes and Plutonyl(VI)-tris-nitrate

Electronic structures and magnetic properties of actinyl ions AnO(2)(n+) (An = U, Np, and Pu) and the equatorially coordinated carbonate complexes [UO2(CO3)(3)](5-), [NpO2(CO3)(3)](4-), and [PuO2(CO3)(3)](4-) are investigated by ab initio quantum chemical calculations. The complex [PuO2(NO3)(3)](-) is also included because of experimentally available g-factors and for comparison with a previous study of [NpO2(NO3)(3)](-) (Chem.-Eur. J. 2014, 20, 7994-8011). The results are rationalized with the help of crystal-field (CF)-type models with parameters extracted from the ab initio calculations, and with the help of natural orbitals and natural spin orbitals contributing to the magnetic properties and the unpaired spin distribution, generated from the spin-orbit wave functions. These orbitals resemble textbooklike representations of the actinide 5f orbitals. Calculated paramagnetic susceptibilities are used to estimate dipolar C-13 chemical shifts for the carbonate ligands. Their signs and order of magnitude are compared to paramagnetic effects observed experimentally in NMR spectra. The results indicate that the experimental spectra are also influenced by contact shifts.