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.