Temperature Dependence of 1H Paramagnetic Chemical Shifts in Actinide Complexes, Beyond Bleaney's Theory: The AnVIO22+–Dipicolinic Acid Complexes (An=Np, Pu) as an Example

• Published in: Chemistry : a European journal 2021-04, Vol.27 (24), p.7138-7153
• Main Authors: Autillo, Matthieu, Islam, Md. Ashraful, Héron, Julie, Guérin, Laetitia, Acher, Eleonor, Tamain, Christelle, Illy, Marie‐Claire, Moisy, Philippe, Colineau, Eric, Griveau, Jean‐Christophe, Berthon, Claude, Bolvin, Hélène
• Format: Article
• Language: English
• Subjects: ab initio calculations; actinide; Chemistry; Energy gap; First principles; Magnetic measurement; Magnetic moments; Magnetic permeability; Magnetic properties; Magnetic resonance spectroscopy; Magnetic susceptibility; Magnetism; NMR; NMR spectroscopy; Nuclear magnetic resonance; paramagnetic NMR spectroscopy; Protons; Solid phases; SQ Bleaney's theory; Superconducting quantum interference devices; Temperature dependence; Tensors
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202005147

Actinide +VI complexes (AnVI =UVI , NpVI and PuVI ) with dipicolinic acid derivatives were synthesized and characterized by powder XRD, SQUID magnetometry and NMR spectroscopy. In addition, NpVI and PuVI complexes were described by first principles CAS based and two‐component spin‐restricted DFT methods. The analysis of the 1H paramagnetic NMR chemical shifts for all protons of the ligands according to the X‐rays structures shows that the Fermi contact contribution is negligible in agreement with spin density determined by unrestricted DFT. The magnetic susceptibility tensor is determined by combining SQUID, pNMR shifts and Evans’ method. The SO‐RASPT2 results fit well the experimental magnetic susceptibility and pNMR chemical shifts. The role of the counterions in the solid phase is pointed out; their presence impacts the magnetic properties of the NpVI complex. The temperature dependence of the pNMR chemical shifts has a strong 1/T contribution, contrarily to Bleaney's theory for lanthanide complexes. The fitting of the temperature dependence of the pNMR chemical shifts and SQUID magnetic susceptibility by a two‐Kramers‐doublet model for the NpVI complex and a non‐Kramers‐doublet model for the PuVI complex allows for the experimental evaluation of energy gaps and magnetic moments of the paramagnetic center. NMR spectroscopy: The temperature dependence of paramagnetic 1H NMR chemical shifts are measured and modelled in the AnVIO22+–dipicolinic acid complexes. Only the pseudocontact term is non‐zero. The magnetic susceptibility tensor, the energy states and magnetic moments of the paramagnetic center are deduced and compared to the SO‐CASPT2 values.