Basicity, complexation ability and interfacial behavior of BTBPs: a simulation study

Area of Science:

• Coordination Chemistry
• Nuclear Fuel Cycle Chemistry
• Separation Science

Background:

• Tetradentate heterocyclic ligands, specifically bis-triazinyl pyridines (BTBPs), are crucial for separating trivalent actinides from lanthanides.
• Understanding ligand behavior, including conformational properties and complexation, is key to optimizing separation processes.

Purpose of the Study:

• To investigate the conformational properties, basicity, and complexation energies of BTBP derivatives and their analogues (BTPhen) with Eu(III).
• To explore the interfacial behavior of a specific BTBP derivative (CyMe(4)BTBP) in its neutral and protonated states at the aqueous-organic interface.
• To elucidate the mechanism of Eu(III) extraction by BTBPs and compare their efficiency with BTPhen ligands.

Main Methods:

• Quantum mechanics (QM) calculations were employed to study conformational properties, basicity, and complexation energies.
• Molecular dynamics (MD) simulations were used to investigate interfacial behavior at the aqueous-organic interface.
• Comparison of BTBP derivatives with alkyl substituents to cis-locked BTPhen analogues.

Main Results:

• Cis-locked BTPhen analogues exhibit higher basicity and form more stable complexes with Eu(III) compared to BTBP derivatives.
• The neutral BTBP ligand shows no surface activity, while protonated and complexed forms are surface-active.
• Eu(III) extraction by BTBPs occurs at the interface via the protonated ligand under acidic conditions.

Conclusions:

• The preorganization of BTPhen ligands contributes to their superior performance in complexation and extraction.
• The interfacial complexation mechanism explains the slow extraction kinetics observed with BTBPs.
• BTPhen ligands are more efficient extractants than BTBPs for trivalent actinides and lanthanides separation.