Berkelium redox speciation

Summary The inner-sphere hydration environments of the Bk 3+ · n H 2 O and Bk 4+ · n ′H 2 O aquo ions in 1 M HClO 4 were determined and are viewed in the context of other 5 f (actinide) and 4 f (lanthanide) aquo ions. The formal potential of the Bk 4+ /Bk 3+ redox couple and the reorganization of the hydration sphere, in terms of the average Bk–OH 2 interatomic distances and number of coordinated water molecules ( n and n ′), were determined through in situ X–ray absorption spectroelectrochemistry. The participation of H 2 O in the electrochemical conversion and the rearrangement of the hydration environment upon reduction–oxidation are summarized in the equation: [Bk(OH 2 ) 8 ] 4+ + H 2 O + e − ⇆ [Bk(OH 2 ) 9 ] 3+ . The change of hydration about 249 Bk 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.