The spectrophotometric characteristics of aqueous solutions of α- and β-molybdosilicic acids

Abstract

Knowledge of the spectrophotometric properties of α- and β-molybdosilicic acids is required for analytical and structural chemical studies. These properties have been studied under various conditions. The conditions with respect to pH and molybdate concentration used for the formation of, and during the subsequent investigation of, the acids were studied. At a given pH and molybdate concentration the shapes of the absorption spectra of the two acids are very similar. That part of the spectrum between 370 and 400 nm is independent of molybdate concentration and pH. However, that between 290 and 370 nm is critically dependent on both of these variables. These results suggest that the molybdosilicic acids form charge-transfer or other complexes with molybdate species in solution. The implications of these findings, which conflict with the results obtained by most previous workers, are discussed.