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

Abstract

We report on the discovery of the first two examples of cationic palladium(II)-oxo clusters (POCs) containing f-metal ions, [Pd^II₆ O₁₂ M₈ {(CH₃ )₂ AsO₂ }₁₆ (H₂ O)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 {Pd₆ O₁₂ }^12- core that is capped by eight M^IV ions, resulting in a cationic, cubic assembly {Pd₆ O₁₂ M^IV₈ }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 [Pd^II₆ O₁₂ M₈ {(CH₃ )₂ AsO₂ }₁₆ (H₂ O)₈ ]⁴⁺ (M=Ce, Pd₆ Ce₈ ; Th, Pd₆ Th₈ ). We have also studied the formation of host-guest inclusion complexes of Pd₆ Ce₈ and Pd₆ Th₈ 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.

Keywords: Calixarene; Cerium; Host-Guest Complexes; Palladium; Palladium-Oxo Clusters.