Alkaline Earth Guests in Polyoxopalladate Chemistry: From Nanocube to Nanostar via an Open-Shell Structure

The three novel, discrete palladium(II)‐oxo clusters [CaPd12O8(PhAsO3)8]6− (CaPd12), [SrPd12O6(OH)3(PhAsO3)6(OAc)3]4− (SrPd12), and [BaPd15O10(PhAsO3)10]8− (BaPd15) encapsulating alkaline earth metal ions were prepared and fully characterized by a multitude of solution and solid‐state physicochemical techniques. We have discovered a structure‐directing template effect induced by the respective size of the alkaline earth guest ion, which determines the detailed condensation arrangement of the peripheral PdII‐oxo shell. The unprecedented SrPd12 with an open‐shell type structure is of particular importance and reflects a successful strategy for deliberate design of new structural classes of polyoxo‐noble‐metalates. Furthermore, the unusual acetate–water ligand exchange phenomenon renders SrPd12 as a promising candidate for noble‐metal‐based catalysis. The noble template effect: The size of the alkaline earth metal ion guest (Ca2+, Sr2+, Ba2+) allows the shape and size of the resulting polyoxopalladate cluster to be tuned. The small Ca2+ ion leads to the 12‐palladate nanocube, the large Ba2+ ion leads to the 15‐palladate nanostar, and the intermediate‐sized Sr2+ ion leads to an intermediary structure, an open‐shell 12‐palladate.