Possibility of the existence of divalent actinium in aqueous solution

Radiopolarographic reduction of Ac(III) was investigated in aqueous solutions. It was found that a very large shift of the half-wave potential was induced by the addition of 1, 4, 7, 10, 13, 16-hexaoxacyclooctadecane (18-CROWN-6) to the aqueous solution. The shift was explained by complex formation of Ac(II) with 18-CROWN-6. The ionic radius and the electronic configuration of Ac²⁺ were determined to be 1.25 Å and [Rn] 6d¹.