, Volume 291, Issue 5, pp 1219-1226
Date: 18 Nov 2012

Interaction of polyoxometalates with linear polyamines

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Polyoxometalates (POMs) are inorganic metal oxoanions with a negative charge, stabilized in the solid state by the corresponding number of countercations and possibly protons. In aqueous solution, the dissociation of all ion pairs is not necessarily quantitative because this would result in strong electrostatic repulsion among the polyanions. In the present communication, we show that the effective charge of the donut-shaped 30-tungsto-5-phosphate [NaP5W30O110]14− (P5W30) is close to its “structural charge” of 14 elementary negative charges in the presence of linear polyamines, namely, poly(allylamine hydrobromide) and poly(l-lysine hydrobromide) in a 10-mM NaBr electrolyte. When phase separation occurs, leading to a precipitate (rich in polyanion) and an almost clear supernatant, the charge ratio of the number of moles of cationic groups to polyanion is close to 14, showing that the effective charge in a solution of P5W30 is indeed equal to −14e in the presence of polycations.