Discrete, Cationic Palladium(II)-Oxo Clusters via f-Metal Ion Incorporation and their Macrocyclic Host-Guest Interactions with Sulfonatocalixarenes

We report on the discovery of the first two examples of cationic palladium(II)-oxo clusters (POCs) containing f-metal ions, [(Pd6O12M8)-O-II{(CH3)(2)AsO2}(16)(H2O)(8)](4+) (M=Ce-IV, Th-IV), and their physicochemical characterization in the solid state, in solution and in the gas phase. The molecular structure of the two novel POCs comprises an octahedral {Pd6O12}(12-) core that is capped by eight M-IV ions, resulting in a cationic, cubic assembly {Pd6O12M8IV}(20+), which is coordinated by a total of 16 terminal dimethylarsinate and eight water ligands, resulting in the mixed Pd-II-Ce-IV/Th-IV oxo-clusters [(Pd6O12M8)-O-II{(CH3)(2)AsO2}(16)(H2O)(8)](4+) (M=Ce, Pd6Ce8; Th, Pd6Th8). We have also studied the formation of host-guest inclusion complexes of Pd6Ce8 and Pd6Th8 with anionic 4-sulfocalix[n]arenes (n=4, 6, 8), resulting in the first examples of discrete, enthalpically-driven supramolecular assemblies between large metal-oxo clusters and calixarene-based macrocycles. The POCs were also found to be useful as pre-catalysts for electrocatalytic CO2-reduction and HCOOH-oxidation.