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

Abstract

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 2S+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−