In Search of Covalency Measure of Gd(III)-Ligand Interactions

• Published in: The journal of physical chemistry letters 2024-09, Vol.15 (38), p.9723-9737
• Main Authors: Janicki, Rafał, Siczek, Miłosz, Starynowicz, Przemysław
• Format: Article
• Language: English
• Subjects: Letter; Physical Insights into Materials and Molecular Properties
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.4c01903

Experimental electron density distribution of the [C­(NH2)3]3[Gd­(EDTA)­F2]·H2O crystal was determined. The derived experimental and theoretical (DFT) topological parameters such as ∇2ρc, ρc, bond degree (BD), kinetics, and potential energy were used to study the nature of Gd–O, Gd–F, and Gd–N interactions. The natural charge of the Gd is 1.86; the natural configuration of the cation is [Xe]­6s0.134f7.105d0.83, and the covalency of the Gd–L bond is mainly connected with the transfer of charge from the sp x ligand orbitals onto the 5d orbitals of the Gd cation. Simultaneously, the donation of charge onto the 6s and 4f orbitals occurs to a lesser extent. Moreover it was found that the donation of the ligand charges onto the Gd­(III) is larger for compounds with a lower coordination number. The obtained topological parameters were analyzed in the context of the Gd­(III) f–f transition properties, i.e., energy of the excited 2S+1LJ states, Judd–Ofelt intensity parameters, and luminescence lifetimes, of 18 Gd­(III) compounds with various O, N, and F donor ligands (DOTA, EDTA, CDTA, DTPA, NTA, EGTA, ODA, F–, H2O, and CO3 2–). The calculated nephelauxetic β parameter may reflect the penetration degree of electron lone pairs of ligands inside the metal basin. Finally, it was found for the first time that the sum of the Gd­(III)–L bond energy (∑E GdL) is correlated with the position of the gravity center of the 8S7/2 → 2S+1LJ transitions and increase of covalency of the Gd­(III)–L bonds is associated with decrease of their bond energy. The obtained results may shed light on chemical bonding in systems containing f-elements. Such subtle differences in the covalent contribution to the Ln–L or An–L bond may tune the selectivity of the partitioning processes of lanthanides and actinides.