Self-assembled M24L48 polyhedra and their sharp structural switch upon subtle ligand variation.

Self-assembly is a powerful technique for the bottom-up construction of discrete, well-defined nanoscale structures. Large multicomponent systems (with more than 50 components) offer mechanistic insights into biological assembly but present daunting synthetic challenges. Here we report the self-assembly of giant M24L48 coordination spheres from 24 palladium ions (M) and 48 curved bridging ligands (L).

Remarkable stabilization of M(12)L(24) spherical frameworks through the cooperation of 48 Pd(II)-pyridine interactions.

Kinetic studies on the ligand exchange of self-assembled M(12)L(24) 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 M(12)L(24) complexes are much longer than those for comparable monodentate Pd(II)-pyridine complexes by a factor of approximately 10(5), suggesting that, once formed, the 36-component molecular spheres behave like covalent componds.