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, H 2 MoO 4 , H 3 MoO 4 + , H 3 MoO 4 Cl, MoO 2 Cl 2 , and MoO 2 Cl 3 - , 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 (H 2 Mo 2 O 5 2+ ), log β = 3.60 ± 0.04 (H 3 Mo 2 O 5 3+ ), and log β = 2.91 ± 0.03 (H 3 Mo 2 O 6 Cl 2+ ).