Speciation of Molybdenum(VI) in Chloride Media at Elevated Mo Concentrations.

Speciation of Mo(VI) in chloride media (0.5-11 M HCl) at elevated Mo concentrations (0.1-300 mM Mo) was investigated using UV spectroscopy. In addition to five major monomeric species, H2MoO4, H3MoO4 +, H3MoO4Cl, MoO2Cl2, and MoO2Cl3 -, chemometric analysis of UV spectra suggests the presence of three cationic dinuclear species that predominate in solutions of 1-4.5 M HCl at >20 mM Mo concentrations. Thermodynamic values and molar absorptivity spectra were calculated from UV spectrophotometric data using refined numerical methods. The stability constants determined for three Mo dimers are log β = 3.53 ± 0.05 (H2Mo2O5 2+), log β = 3.60 ± 0.04 (H3Mo2O5 3+), and log β = 2.91 ± 0.03 (H3Mo2O6Cl2+).