A theoretical study on bonding and energy aspects of and [LnL₃ · H₂O]³⁺ complexes (Ln = La, Eu, Gd, L · u; L = β-diketone, β-dithioketone, β-diphosphine oxide)

Abstract

The interaction of Ln³⁺ cations (La³⁺, Eu³⁺, Gd³⁺ and Lu³⁺) with bidentate model ligands L (L = β-diketone (β-CO), β-thiodiketone (β-CS) and β-phosphine oxide (β-PO)) has been investigated using density functional theory (DFT/B3PW91) and the MP2 method. The metal–ligand bonds have been investigated with the help of the quantum theory of atoms in molecules (QTAIM) and an energy decomposition analysis. On the basis of the QTAIM results, it can be concluded that, although being mainly ionic, the Ln–L bond can present donation and back-donation that can be assessed separately. Moreover, there is a little more S to Ln sigma donation than O to Ln sigma donation and the donation interaction increases in the order β-CO < β-PO < β-CS. The role of water molecule coordination is also investigated by a comparison of the and [LnL₃ H₂O]³⁺ complexes. The mean LnL distances increase slightly from to [LnL₃ H₂O]³⁺. Both the B3PW91 and MP2 methods reveal that the addition of a water molecule to complexes leads to a marked decrease in the LnL interaction energies due to the additional charge donation of the water molecule towards Ln and the increased steric crowding around the cation.

Keywords:

• lanthanide
• β-diketone
• β-phosphine oxide
• Bader theory
• EDA