Assembly of a Heterometallic Cu(II)-Pd(II) Cage by Post-assembly Metal Insertion

Porous structures based on multi-metallic motifs are receiving growing interest, but their general preparation still remains a challenge. Here, we report the self-assembly and structure of a Cu^II metal-organic cage (MOC) that is functionalized with free bis(pyrazolyl)methane sites. The homometallic Cu₄L₄ cage is isolated as a water-stable crystalline solid, and its formation is dependent on metal-ligand stoichiometry and the pre-organization of the Cu₂ paddlewheel. We show by X-ray diffraction and SEM-EDX that Pd^II chloride can be quantitatively inserted into the free chelating sites of the MOC to yield a [Cu₄(L(PdCl₂))₄] structure. Moreover, the solvent employed in the metalation dictates the solid-state isomerism of the heterometallic cage─a further handle to control the MOC's structural diversity and permanent porosity.