Self-assembly and structural transformations of high-nuclearity palladium-rich polyoxometalates

A one-pot strategy exploiting the structure directing effects of Se-IV and Te-IV heteroatoms has yielded the highest nuclearity noble metal containing polyoxometalates to date; including the palladium-rich seleno-tungstate isomers K-28[H12Pd10Se10W52O206]center dot 65H(2)O (1) and K-26[H14Pd10Se10W52O206]center dot 68H(2)O (2), and the nanoscale tellurotungstate cluster Na-40[Pd6Te19W42O190]center dot 76H(2)O (3). These reaction systems exhibit remarkable structural flexibility and point to a new route towards the synthesis of complex heterometallic species, in which multiple lacunary polyoxometalate 'building blocks' have been assembled to trap a transient oxopalladate species suspected to play a role in the assembly of several common polyoxopalladates. Mass spectrometry has been applied to explore and compare the solution stability of compounds 1-3, demonstrating the markedly different properties of the Se-IV and Te-IV templated systems. Electrochemical analysis of 1 has been provided and is dominated by Pd redox processes, with reduction of the cluster resulting in electrodeposition of Pd metal and observation of the subsequent formation of PdO species, concurrent with previously reported oxopalladate containing species.