Stabilization of Plutonium(III) in the Preyssler Polyoxometalate

Abstract

The Na(+) ion encapsulated within the Preyssler heteropolyoxoanion, [NaP5W30O110](14-), was exchanged with Pu(III) under hydrothermal conditions to obtain [Pu(III)P5W30O110](12-) (abbreviated [PuPA](12-)) with hybrid electrochemical properties resulting from the combination of the key redox behaviors of the Pu cation and the P-W-O anion. The electroanalytical chemistry of this two-center, multielectron redox system in a 1 M HCl electrolyte shows that Pu(III) is oxidized to Pu(IV) at the half-wave potential, E(1/2), of +0.960 V versus Ag/AgCl, which is 0.197 V more positive than the corresponding electrode potential for the Pu(III) aqua ion also in 1 M HCl, indicating the stabilization of the trivalent Pu cation by its encapsulation in the Preyssler polyoxometalate (POM). This effect is uncommon in actinide-POM chemistry, wherein electrode potential shifts of the opposite nature (to more negative values), leading to the stabilization of the tetravalent ions by complexation, are renowned. Moreover, in cyclic voltammetry measurements of the Pu(III) aqua ion and [PuPA](12-), the peak currents, i(p), for the one-electron Pu(III)/Pu(IV) processes show different dependencies with the scan rate, nu. The former shows proportionality with nu(1/2), indicating freely diffusing species, whereas the latter shows proportionality with nu, indicating a surface-confined one. The first of the five successive two-electron, W-centered reduction processes in [PuPA](12-) occurs at E(1/2) = -0.117 V versus Ag/AgCl, which is 1.077 V less than the E(1/2) for the Pu(III)/Pu(IV) oxidation, thereby providing an experimental, electrochemical measure of the highest occupied molecular orbital/lowest unoccupied molecular orbital energy gap, which compares well with values previously obtained by density-functional theory, complete active space-self consistent field, and post-Hartree-Fock calculations for a series of M(n+)-exchanged systems, [MPA](n-15) for 1 < or = n < or = 4 (Fernandez, J. A.; Lopez, X.; Bo, C.; de Graff, C.; Baerends, E. J.; Poblet, J. M. J. Am Chem. Soc. 2007, 129, 12244-12253). It was not possible to prepare the Np-exchanged Preyssler anion in the manner of [PuPA](12-), because of the instability of tri- and tetravalent Np to oxidation and the formation of the neptunyl(V) ion, which also could not be exchanged for Na(+).

A Journey inside the U28 Nanocapsule

“…This quasireversible process was attributed to the oxidation of the innermost peroxo ligands; the removal of electrons from the peroxo‐based HOMOs would lead to the formation of a superoxo complex that would be prone to disproportionation were it not stabilized by uranyl(V), as in calculations reported previously 14. In so far as the difference between the applied electrode potentials for the first reduction ( E pc =−0.99 V) and the first oxidation (−0.14≤ E 1/2 ≤−0.12 V) provided an electrochemical measure of the HOMO–LUMO gap,15 the experimental value of 0.9 V compares favorably with the calculated values (Table 2). Moreover, the calculated band‐gap of U@NaRbU 28 (1.1 eV) matches the value observed by electrochemical analysis.…”

Mesoporous Manganese Sulfide Spheres Anchored on Graphene Sheets as High‐Capacity and Long‐Life Anode Materials for Lithium‐Ion Batteries

“…It has been known that the encapsulated Na + is exchangeable with other cations such as Ca 2+ , Y 3+ , lanthanides, Bi 3+ , and actinides, and stability was expected to be increased by the exchange 4,15–17. Herein, we report synthesis and characterization of Preyssler‐type phosphotungstic acid with different encapsulated cations of Ca 2+ , Y 3+ , Ce 3+ , Eu 3+ , and Bi 3+ , and their thermal stabilities, acidic strength, and catalytic activities for hydrolysis activities of ethyl acetate and cellobiose.…”

Symmetry versus Minimal Pentagonal Adjacencies in Uranium‐Based Polyoxometalate Fullerene Topologies

“…Polyoxometalates are centuries old, [1] and Keggin established the first structure of a heteropolyoxometalate compound in 1933. [2] Actinides have recently been incorporated into polyoxometalates of transition metals, [3][4][5][6][7] but only three studies report actinide-based polyoxometalate clusters. [8][9][10] Yet actinides are ideal candidates for self-assembly into clusters that may possess interesting properties associated with the complexity of the f electrons, and such clusters could be useful in the nuclear fuel cycle.…”