Electronic structure and complexation behavior of methyl substituted phosphonate ligands with uranyl nitrate

Abstract

Quantum chemical calculations were applied to investigate the electronic structures and complexation behaviour of methyl-substituted phosphonic acids with uranyl (VI) nitrate. The Natural Bond Orbital (NBO) analysis indicated that the methyl groups in substituted phosphonic acids exhibit electron-withdrawing properties. Additionally, the methyl groups directly bonded to the phosphoryl P atom prefer a gauche orientation relative to the P=O group in compounds such as MPn, DMMP and DMPn. Weak to moderate H-bonding interactions provided extra stability to Pn, MHPn, MPn and DMPn complexes with U(VI). The ν(P=O) values were red-shifted in all the complexes, implying a moderate weakening of the P=O bond upon complexation. Furthermore, the complexation energy values indicated an increasing complexation tendency in 1:2 complexes, particularly when the methyl groups were introduced. This trend was observed in the sequence Pn → MHPn → MPn and DMHP → DMMP → DMPn.

Keywords

• Phosphonate
• Uranium
• Complexation energies
• DFT
• NBO
• Electronic structure