A Pd₂₄ Pregnant Molecular Nanoball: Self-Templated Stellation by Precise Mapping of Coordination Sites

We found that Pd­(II) ion (M) and the smallest 120° bidentate donor pyrimidine (L_a) self-assemble into a mononuclear M(L_a)₄ complex (1a) instead of the expected smallest M₁₂(L_a)₂₄ molecular ball (1), presumably due to the weak coordination nature of the pyrimidine. To construct such a pyrimidine bridged nanoball, we employed a new donor tris­(4-(pyrimidin-5-yl)­phenyl)­amine (L); which upon selective complexation with Pd­(II) ions resulted in the formation of a pregnant M₂₄L₂₄ molecular nanoball (2) consisting of a pyrimidine-bridged Pd₁₂ baby-ball supported by a Pd₁₂ larger mother-ball. The formation of the baby-ball was not successful without the support of the mother-ball. Thus, we created an example of a self-assembly where the inner baby-ball resembling to the predicted M₁₂(L_a)₂₄ ball (1) was incarcerated by the giant outer mother-ball by means of geometrical constraints. Facile conversion of the pregnant ball 2 to a smaller M₁₂(L_b)₂₄ ball 3 with dipyridyl donor was achieved in a single step.