Reactivity, Formation, and Solubility of Polyoxometalates Probed by Calorimetry.

Room temperature calorimetry methods were developed to describe the energy landscapes of six polyoxometalates (POMs), Li-U, Li-U, K-U, Li/K-U, Mo, and Mo, in terms of three components: enthalpy of dissolution (Δ), enthalpy of formation of aqueous POMs (Δ), and enthalpy of formation of POM crystals (Δ). Δ is controlled by a combination of cation solvation enthalpy and the favorability of cation interactions with binding sites on the POM. In the case of the four uranyl peroxide POMs studied, clusters with hydroxide bridges have lower Δ and are more stable than those containing only peroxide bridges. In general for POMs, the combination of calorimetric results and synthetic observations suggest that spherical topologies may be more stable than wheel-like clusters, and Δ can be accurately estimated using only Δ values owing to the dominance of the clusters in determining the energetics of POM crystals.