Selective Construction of Magic Hierarchical Metal–Organic Clusters on Surfaces

Abstract

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.

Synthesis of the Two-Dimensional Robust Kagome Lattice on Au(111) via the Introduction of Fe Atoms

“…[38][39][40]44 The interactions between the amino groups and the carboxyl groups are rather weak, through the N−H•••O hydrogen bonds. 44,45 In addition, the STM images of the amino groups containing molecules are fuzzy on Au(111) at 77 K (Figure S1), suggesting both the interactions between the amino groups and the molecule−substrate interactions are neglectable. Based on the above discussion, we obtained the optimized structure of the α phase, as shown in Figure 1c.…”

“…This fact agrees with previous reports that neither deprotonation nor covalent coupling of the carboxylic acids was observed after thermal treatment on Au(111). 39,45 The significant desorption suggests relative weak molecule− molecule and molecule−substrate interactions, leading to the (3,6,3,6) Kagome lattice shown in Figure 1 being thermally unstable. In addition to this, the presence of numerous domain boundaries in the α phase prevents the formation of large-scale domains.…”

“…45,47,48 The Fe atoms prefer to interact with the carboxyl groups, rather than the amino groups. 45 We therefore obtained the optimized structure of the β phase. As shown in Figure 3c, two deprotonated carboxyl groups are connected with each other via one iron atom through the O−Fe bonds, leading to ABPCA dimers.…”

Role of the Structure and Reactivity of Cu and Ag Surfaces in the Formation of a 2D Metal–Hexahydroxytriphenylene Network

“…By taking advantage of the directional bonding of specific molecule–molecule and/or molecule–surface interactions and by choosing the appropriate symmetry for the molecules and the electronic properties of the surfaces, remarkable 2D extended structures have been achieved. − These structures are mainly observed by scanning probe microscopies under ultrahigh vacuum (UHV) conditions in order to reach submolecular resolution to unambiguously identify the designed structures. Among all possibilities to create ordered structures on a surface, the complexation with metal atoms has been widely used. − In this case, the formation of metal–organic networks, consisting in oxygen-bearing molecular units interconnected via metallic centers, has been widely explored at the surface of metals under UHV conditions. , The required metal atoms are provided either extrinsically by on-surface metal evaporation or intrinsically by the metal surface itself. Noteworthily, in the latter case, the coordination mechanism is activated by the oxidation of the molecular precursor that takes place spontaneously in UHV due to the electronic properties of the supporting surface.…”

Scanning Tunneling Microscopy and Computational Simulation Studies of a Fluorenone-Based Organic Optoelectronic Material

“…In recent years, surface supramolecular self-assembly has been an intensively studied topic owing to its potential applications including surface modification, molecular-based devices, and two-dimensional (2D) crystal engineering. − Self-assembly is an effortless means for surface patterning, which involves reversible noncovalent interactions, and is a process where molecules adsorb onto and desorb from an atomically flat surface, for example, highly oriented pyrolytic graphite (HOPG), Au (111), Ag (111), and Cu (110). − The underlying driving forces include hydrogen bonds, halogen bonds, van der Waals interactions, and π–π attractions. − Scanning tunneling microscopy (STM) is the main analytical tool used due to its submolecular resolution.…”