Rational Design of Organically Functionalized Polyoxopalladates and Their Supramolecular Properties.

The SrII -centered 12-palladate(II) open-cube {SrPd12 (OAc)3 } has been systematically evolved by substitution of the three acetate ligands by a library of saturated carboxylic acids with increasing chain lengths leading to four novel polyoxopalladates(II) with the formula [SrPd12 O6 (OH)3 (PhAsO3 )6 (L)3 ]4- (SrPd12 L3 , L=Cn H2n+1 COO, n=2 to 5). These first examples of surfactant-type polyoxopalladates with a hydrophilic metal-oxo unit and three hydrophobic alkyl chains were characterized in the solid state (single-crystal XRD, FTIR, TGA), in solution (1 H,13 C NMR spectroscopy), and in the gas phase (ESI-MS). The two polyanions SrPd12 L3 with chain lengths of 5 and 6 are the first examples of polyoxopalladates that are soluble and stable in organic media. The Na salts of the amphiphilic polyoxopalladates SrPd12 L3 were shown to self-assemble into "blackberry"-type spherical supramolecular structures in dilute solutions, of which an unusual "volcano"-shaped trend of assembly size versus solvent polarity is chiefly influenced by directional hydrogen bonding interactions.