Selective Construction of Magic Hierarchical Metal–Organic Clusters on Surfaces

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Magic organic clusters, representing well-defined zero-dimensional organic clusters with identical sizes and configurations, have received increased interests in recent years. Previously, the magic clusters were mainly stabilized through van der Waals force, C–H...π interaction, hydrogen bonding, dipole interaction, etc., which yet lack thermal stability and tunable electronic transport properties for potential applications. The introduction of metal adatoms into the organic systems would be an excellent choice for facilitating more stable magic clusters as the metal adatoms could serve as a nucleation center and help for clustering of organic ligands with increased stabilities. Considering the limited coordination number of metal species, it would be of great interest to introduce multilevel interactions besides metal–organic bonding, which may provide new avenues for controllable fabrication of more complicated and larger magic clusters. Herein, we have achieved the controllable fabrication of three distinct magic metal–organic clusters, especially two hierarchical ones with different sizes on the reconstructed Au(111) and unreconstructed Ag(111) surface. The key for various unprecedented magic hierarchical clusters here is the selection of the organic ligands with only one active carboxyl (−COOH) group which possesses bonding flexibility and diversity features after dehydrogenation but avoids the usual two-dimensional network of those containing more −COOH groups.