Electrochemical study of mendelevium in aqueous solution: No evidence for monovalent ions

Abstract

The report by Mikheev et al. [1] of a stable, monovalent, cesium-like ion of mendelevium is in conflict with recent estimates of the relative stability of Md +, based on electrochemical systematics of the actinide series. To clarify this situation, experiments using controlled-potential electrolysis were undertaken at Oak Ridge National Laboratory to study the over-all reduction mechanism of Md 3+ to the amalgam. Half-wave amalgamation potentials were measured by radiocoulometry in the presence of weak (acetate) and strong (citrate) complexing agents. The half-wave potentials with respect to the normal hydrogen electrode were found to be −1.49 ± 0.01 V in acetate and −1.60 ± 0.01 V in citrate solutions. The results showed that Md behaved analogously to Fm, which has been shown to undergo electrode reduction in two steps, 3+→2+ and 2+→0. The half-wave potentials observed for Md are believed to be characteristic of the reduction 2+→0. Further, the shift in the half-wave potential of mendelevium caused by a strong complexing agent is too large to be explained by reduction of a cesium-like, monovalent ion.