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

The report 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 to study the over-all reduction mechanism of Md3+ 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. (author)