Spontaneous Partitioning of Californium from Curium: Curious Cases from the Crystallization of Curium Coordination Complexes

The reaction of (CmCl3)-Cm-248 with excess 2,6-pyridinedicarboxylic acid (DPA) under mild solvothermal conditions results in crystallization of the tris-chelate complex Cm(HDPA)(3)center dot H2O. Approximately half of the curium remains in solution at the end of this process, and evaporation of the mother liquor results in crystallization of the bis-chelate complex [Cm(HDPA)(H(2)DPA)(H2O)(2)Cl]Cl center dot 2H(2)O. Cm-248 is the daughter of the alpha decay of Cf-252 and is extracted in high purity from this parent. However, trace amounts of Cf-249,Cf-250,Cf-251 are still present in all samples of Cm-248. During the crystallization of Cm(HDPA)(3)center dot H2O and [Cm(HDPA)(H(2)DPA)(H2O)(2)Cl]Cl center dot 2H(2)O, californium(III) spontaneously separates itself from the curium complexes and is found doped within crystals of DPA in the form of Cf(HDPA)(3). These results add to the growing body of evidence that the chemistry of californium is fundamentally different from that of earlier actinides.