Lanthanoid-, Yttrium-, and Thorium-Centered Polyoxopalladates

Polyoxopalladates (POPs) are an extension of classic polyoxometalates. The two most frequently observed POP topologies are the nanostar (Pd₁₅) and the cube (Pd₁₂), where the heterometal cation in the central cavity may influence topology selection. Here, we crystallize ten lanthanoid-centered, phenylphosphonate-capped POPs (Y^III, La^III, Ce^III, Pr^III, Nd^III, Sm^III, Eu^III, Gd^III, Yb^III, and Lu^III) and one actinide-centered (Th^IV) POP. Single-crystal X-ray analysis reveals that most Ln^III favors the Pd₁₅ nanostar, while Yb and Lu favor the Pd₁₂ cube. Between Tb and Tm, no single-crystal growth occurred, challenging our initial hypothesis that topology selection was entirely based on the central metal cation size. Computation supported this hypothesis; the transition from Pd₁₅ to Pd₁₂ as the favored topology occurs in the third quarter of the lanthanide series. On the other hand, PXRD of all the crystallized/precipitated bulk materials suggested Pd₁₅ is always the favored topology, and inspection of the lattices reveals that Pd₁₅-Na interactions likely promote incipient crystallization, while no such interactions are seen in the Pd₁₂ lattices. Electrospray ionization mass spectrometry confirmed the presence of both Pd₁₂ and Pd₁₅ for the smaller lanthanides (Yb), only Pd₁₅ for the larger lanthanides (Ce), and no clusters were observed between Tb and Tm, where crystal growth was also challenging.