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Thermodynamical Criteria of the Higher Selectivity of Zirconium Oxycations over Hafnium Oxycations towards Organophosphorus Ligands: Density Functional Theoretical Investigation
Author(s) -
Ali Sk. Musharaf
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201301630
Subject(s) - chemistry , solvation , density functional theory , valence (chemistry) , selectivity , zirconium , basis set , aqueous solution , ion , inorganic chemistry , computational chemistry , organic chemistry , catalysis
Density Functional theory (DFT) has been used to optimize the structures of Cyanex925 [bis(2,4,4‐trimethylpentyl)octylphosphine oxide], tributyl phosphate (TBP), and their complexes with Hf and Zr oxycations by employing the triple‐zeta valence plus polarization (TZVP) basis set. The effect of noncovalent interactions was examined by using the TPSSH and M06‐2X density functionals. The free energy of extraction Δ G ext from the aqueous to organic phase was calculated by using the standard thermodynamic procedure in conjunction with the conductor‐like screening model (COSMO). The calculated Δ G ext , either with an implicit or explicit solvation model, fails to capture the experimentally reported preferential selectivity of ZrO 2+ ions over HfO 2+ ions in the absence of nitrate anions towards Cyanex925 over TBP. The presence of nitrate anions along with the second solvation shell ( n = 6 + 1 water molecules) around the oxycation shows consistent results with the calculated Δ G ext for the selectivity as reported in solvent extraction experiments [the calculated ΔΔΔ G ext value (–4.72 kcal/mol) is in qualitative agreement with the experimental ΔΔΔ G ext (–0.82 kcal/mol) results; separation factor (SF) ≈ exp(–ΔΔΔ G ex / RT )]. Different bonding analyses indicate the electrostatic nature of the interactions between the metal oxycations and the organophosphorus ligands. The present study will further assist in the design of new ligand/solvent systems for the preferential extraction of ZrO 2+ ions over HfO 2+ ions in solvent extraction experiments.