Remarkable stabilization of M₁₂L₂₄ spherical frameworks through the cooperation of 48 Pd(II)-pyridine interactions

Kinetic studies on the ligand exchange of self-assembled M ₁₂L₂₄ spherical complexes demonstrate that the multicomponent self-assembly roughly undergoes three stages. Initially, (i) there are very rapid equilibrations (ms^-1) among the many components; (ii) as more stable structures are formed, the system equilibrates quickly (s^-1 to min^-1) among the completed and uncompleted self-assemblies; misassembled structures are presumably corrected at this stage; and finally (iii) very slow equilibration (hours to days) at the final stage after the self-assembly completes, producing the kinetic stability of the whole. The half-lives of the ligand exchange processes in the M₁₂L ₂₄ complexes are much longer than those for comparable monodentate Pd(II)-pyridine complexes by a factor of ∼10⁵, suggesting that, once formed, the 36-component molecular spheres behave like covalent componds.