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

Rafał JanickiMiłosz SiczekPrzemysław Starynowicz
Published in: The journal of physical chemistry letters (2024)
Experimental electron density distribution of the [C(NH 2 ) 3 ] 3 [Gd(EDTA)F 2 ]·H 2 O crystal was determined. The derived experimental and theoretical (DFT) topological parameters such as ∇ 2 ρ c , ρ c , 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]6s 0.13 4f 7.10 5d 0.83 , 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 2 S +1 L J 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 - , H 2 O, and CO 3 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 8 S 7/2 → 2 S +1 L J 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.
Keyphrases
  • density functional theory
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  • crystal structure
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