Studies of lanthanide interactions with polyoxometalates

A plenary (P₂W₁₈O₆₂ 6-) and lacunary (P₂W₁₇O ₆₁10-) polyoxometalate (POM) species were synthesized and analyzed using a variety of standard gravimetric procedures. The polyoxometalate solution chemistry was investigated in the presence of a series of lanthanide cations (La, Nd, Eu, Dy, Er, and Yb) using a variety of physical techniques. The lanthanide complexes have been evaluated with regard to the potential application of the polyoxometalates as model systems for natural water clay particle/colloid interactions with f-elements.; The thermodynamic parameters of complexation (ΔG, ΔH, and ΔS) for all Ln(III) - POM interactions were investigated. The 7F ₀ → 5D₀ selective excitation spectra coupled with the computer program SQUAD, were used to determine the 1:1 and 1:2 stability constants for Eu(III) - POM. A Ln(III) versus Eu(III) competition study was used to determine the 1:1 stability constants for Ln(III) - POM species using the 7F₀ → 5D ₀ selective excitation spectra of Eu(III). The values of ΔG _n (n = 1 or 2) were determined from the stability constant values. Enthalpies of complexation, ΔH_n (n = 1 or 2) were determined using standard enthalpic titration methods. Additionally, the entropy titration method was used for the Ln(III)-P₂W₁₈ system to calculate both the stability constant, log $b1$ (resulting in a calculated value of ΔG), and ΔH. The entropies, ΔS_n (n = 1 or 2) of complexation were calculated from ΔG_n (n = 1 or 2) and ΔH_n (n = 1 or 2) values.; In addition, the 7F₀ → 5D ₀ selective excitation spectra of Eu(III)-POM complexes were evaluated quantitatively. The number of peaks indicates the number of discernible solution species and the corresponding inner sphere H₂O molecules can be determined from lifetime decay measurements.; The Ln(III) - POM interaction was modeled using both the extended Born equation and the charge distribution surface complexation model for insight into the electrostatic interaction between binding species.