Complexation of amidocarbamoyl phosphine oxides with Ln⁺³ (Ln = La, Nd, Pm, Sm and Eu) cation series: structural and thermodynamical features

Abstract

In the present study, we have mainly investigated the nature of interactions in Ln³⁺ (Ln = La, Nd, Pm, Sm, Eu) complexes with amidocarbamoyl methyl phosphine oxide (CMPO) and amidocarbamoyl propyl phosphine oxide (CPPO) ligands based on density functional theory (DFT) approaches. In the first step, thermodynamical properties for complexation of CMPO and CPPO ligands with Ln³⁺ cation series have been determined in the gas phase and with the presence of three solvents: n-hexane, chloroform and toluene, via polarized continuum model (PCM) computations. The trend of metal-ligand interaction strength has been analyzed and compared with the trend of ionic hardness within the series of lanthanide cations and different size of alkyl chain of amidocarbamoyl phosphine oxide ligand. The calculated thermochemical results in the gas and solution phases reveals that there is a consistency between increasing trend in the hardness of Ln³⁺ cation series and also electron-donating property of alkyl chain with increasing in thermodynamical stability of [Ln–CMPO]³⁺ and [Ln–CPPO]³⁺ complex series. We have also demonstrated that in the complexation reaction of all complex series, using n-hexane as solvent is more favorable thermodynamically than chloroform and toluene. It should be stated that this issue has been observed in many experiments. Finally, analysis of calculated deformation energies and also the variation in bond order of some selected key bonds in CMPO and CPPO ligands and their corresponded Ln⁺³ complexes series show a similar trend with increasing in the hardness of Ln³⁺ cation series and electron-donating of alkyl chain of amidocarbamoyl phosphine oxide ligand.