Investigation of neptunium(VI) complexation by SiW11O398- by visible/near infrared spectrophotometry and factor analysis

Neptunium(vi) complexation by a lacunary heteropolyanion (SiW11O398-) in an aqueous medium at pH 1 was investigated by spectrophotometry in two region s of the spectrum: in visible light (540-670 nm) and in the near infrared ( 1120-1260 nm). Principal components analysis (PCA) revealed the formation o f two species depending on the additive ligand in solution: a NpO2(SiW11O39 )(6-) complex and the free species NpO22+ that was initially present at pH 1. Modeling factor analysis (MFA) was used to calculate a similar absolute constant for both wavelength regions: log beta(1)=11.6 +/- 0.1. This techni que was also used to determine the spectrum of the NpO2(SiW11O39)(6-) compl ex formed in aqueous solution.