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Complexation Behavior of the Tri‑n‑butyl Phosphate Ligand with Pu(IV) and Zr(IV): A Computational Study
journal contribution
posted on 2016-06-01, 00:00 authored by Gopinadhanpillai Gopakumar, B. Sreenivasulu, A. Suresh, C. V. S. Brahmmananda
Rao, N. Sivaraman, M. Joseph, Anakuthil AnoopTri-n-butyl phosphate
(TBP), used as the extractant
in nuclear fuel reprocessing, shows superior extraction abilities
for Pu(IV) over a large number of fission products including Zr(IV).
We have applied density functional theory (DFT) calculations to explain
this selectivity by investigating differences in electronic structures
of Pu(NO3)4·2TBP and Zr(NO3)4·2TBP complexes. On the basis of our quantum chemical
calculations, we have established the lowest energy electronic states
for both complexes; the quintet is the ground state for the former,
whereas the latter exists in the singlet spin state. The calculated
structural parameters for the optimized geometry of the plutonium
complex are in agreement with the experimental results. Atoms in Molecules
analysis revealed a considerable amount of ionic character to M–O{TBP}
and M–O{NO3} bonds. Additionally, we have also investigated
the extraction behavior of TBP for metal nitrates and have estimated
the extraction energies to be −73.1 and −57.6 kcal/mol
for Pu(IV) and Zr(IV), respectively. The large extraction energy of
Pu(IV) system is in agreement with the observed selectivity in the
extraction of Pu.