Dipolar and contact paramagnetic NMR chemical shifts in An$^{IV}$ complexes with dipicolinic acid derivatives

• Published in: Inorganic chemistry 2022-06, Vol.61 (27), p.10329-10341
• Main Authors: Islam, Md. Ashraful, Autillo, Matthieu, Guérin, Laetitia, Tamain, Christelle, Moisy, Philippe, Bolvin, Hélène, Berthon, Claude
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Coordination chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c00845

Actinide +IV complexes (AnIV = ThIV, UIV, NpIV, and PuIV) with two dipicolinic acid derivatives (DPA and Et-DPA) have been studied by 1H and 13C NMR spectroscopies and first-principles calculations. The Fermi contact and dipolar contributions to the actinide-induced shifts (AIS) are evaluated from a temperature dependence analysis, combined with ab initio results. It allows an experimental estimation of the axial anisotropy of the magnetic susceptibility Δχax and of the hyperfine coupling constants of the NMR-active nuclei. Due to the compactness of the coordination sphere, the magnetic anisotropy of the paramagnetic center is small, and this makes the contact contribution to be the dominant one, even on the remote atoms. The sign of the hyperfine coupling constants and related spin densities is alternating on the nuclei of the ligand cycle, denoting a preponderant spin polarization mechanism. This is well reproduced by unrestricted density functional theory (DFT) calculations. Those values are furthermore slightly decreasing in the actinide series, which indicates a small decrease of the covalency from UIV to PuIV.