Electrochemistry of berkelium in acidic aqueous solution

Directed evolution of the periodic table: probing the electronic structure of late actinides

Recent investigations of the coordination chemistry and physical properties of berkelium (Z = 97) and californium (Z = 98) have revealed fundamental differences between post-curium elements and lighter members of the actinide series. This review highlights these developments and chronicles key findings and concepts from the last half-century that have helped usher in a new understanding of the evolution of electronic structure in the periodic table.

Berkelium redox speciation

The inner-sphere hydration environments of the Bk3+·nH2O and Bk4+·n′H2O aquo ions in 1 M HClO4 were determined and are viewed in the context of other 5f (actinide) and 4f (lanthanide) aquo ions. The formal potential of the Bk4+/Bk3+ redox couple and the reorganization of the hydration sphere, in terms of the average Bk–OH2 interatomic distances and number of coordinated water molecules (n and n′), were determined through in situ X–ray absorption spectroelectrochemistry. The participation of H2O in the electrochemical conversion and the rearrangement of the hydration environment upon reduction–oxidation are summarized in the equation: [Bk(OH2)8]4+ + H2O + e− ⇆ [Bk(OH2)9]3+. The change of hydration about 249Bk between the trivalent and tetravalent states is believed to reflect predominantly steric factors related to the difference of ionic radii, rather than electronic or bonding influences.