Molybdenum(VI) Coordination in Tributyl Phosphate Chloride Based System

Fundamental coordination
chemistry of Mo­(VI) at its macroconcentrations
in solvent extraction systems is of great importance for industrial
processes that require the purification or recovery of large concentrations
of Mo. The coordination of Mo­(VI) in tri-n-butyl
phosphate (TBP) from solutions of hydrochloric acid and up to 0.3
M Mo was investigated using UV, FTIR, and 31P NMR spectroscopies,
as well as EXAFS. From these techniques we resolved near-neighbor
atoms, speciation, structural information on the coordination environment,
and thermodynamic parameters affiliated with the solvent extraction
of Mo­(VI) and HCl. The solvated extracted form of Mo­(VI) as MoO2Cl2·2TBP was identified. High extraction yield
of Mo at >5 M HCl concentration is driven by replacing HCl in the
organic phase by Mo. The existence of additional organic Mo adducts
is also discussed with the aid of density functional theory, however
no evidence of dimeric or polymeric Mo species was found to be present
in TBP.