Spectrophotometric Investigation of the Interaction of Polyoxometalates with Cationic Dyes

The interaction of a cationic dyes methylene blue (MB) and toluidine blue (TB) in aqueous solution with anionic lacunary polyoxometalate K 7 PW 11 O 39 .14H 2 O (LPOM s ) has been investigated spectrophotometrically. The results showed that when the amounts of LPOM s was increased, the formation of H‒aggregates of dye‒LPOM s complex were obtained. The stoichiometry of MB–LPOM s and TB–LPOM s complex was evaluated using the ratio method and was found to be 1:1. The stability constant of the two complex at 298 K was calculated, and the amount of additives inducing total destabilization of these complexes were determined. Finally, it is quit probably that the interaction mechanism is related to electrostatic interactions between the dyes and the LPOMs.