Characterization of molybdenum compounds in aqueous solution

The reduction reaction chemistry of heptamolybdate with stannous ion was investigated using UV-visible spectroscopy. Absorbance maxima were correlated with calculated crystal field theory values for {dollar}rm Mosp{lcub}V{rcub}, Mosp{lcub}IV{rcub},{dollar} and {dollar}rm Mosp{lcub}III{rcub}{dollar} species. Absorption maxima from 699-714 nm in water and dilute HCl indicated only the presence of {dollar}dsp1{dollar} octahedral complexes. At 393 nm, a {dollar}dsp2{dollar} octahedral complex was formed in 6 M HCl with a large excess of reductant. Finally, a {dollar}dsp3{dollar} complex was detected at 446 nm. The calculation for crystal field splitting energy at 446 nm does not match with either a tetrahedral or octahedral field. A molecular geometry between octahedral and tetrahedral describes this transient {dollar}rm Mosp{lcub}III{rcub}{dollar} complex.