Tetravalent actinides – from polymeric complexes to nanoparticles

Tetravalent actinides show a strong tendency towards hydrolysis. This forces the formation of polynuclear species. However, the polynuclear species undergo further polymerization and form colloids. One way to isolate polynuclear species is to introduce terminating groups which hinder further polymerization. We found that carboxylates are well suited for this task. Larger clusters can form either highly ordered nanoparticles, complete amorphous structures, or transitions between them. Nanoparticles with an ordered structure can be stabilized by the introduction of termination functions, whereas amorphous nanoparticles can be potentially stabilized by introducing ions that modify the surface charge. These modifications support the structure analysis of the species. The nanoparticles of tetravalent actinides can form colloid suspensions which are stable over years. Due to their low solubility, tetravalent actinides are considered as nearly immobile in the nature. The surface charge may significantly enhance their migration.