Self-Assembly of Metallo-Supramolecules under Kinetic or Thermodynamic Control: Characterization of Positional Isomers Using Scanning Tunneling Spectroscopy

Abstract

Coordination-driven self-assembly has been extensively employed to construct a variety of discrete structures as a bottom-up strategy. However, mechanistic understanding regarding whether self-assembly is under kinetic or thermodynamic control is less explored. To date, such mechanistic investigation has been limited to distinct, assembled structures. It still remains a formidable challenge to study the kinetic and thermodynamic behavior of self-assembly systems with multiple assembled isomers due to the lack of characterization methods. Herein, we use a stepwise strategy which combined self-recognition and self-assembly processes to construct giant metallo-supramolecules with 8 positional isomers in solution. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy, we were able to unambiguously differentiate 14 isomers on the substrate which correspond to 8 isomers in solution. Through measurement of 162 structures, the experimental probability of each isomer was obtained and compared with the theoretical probability. Such a comparison along with density functional theory (DFT) calculation suggested that although both kinetic and thermodynamic control existed in this self-assembly, the increased experimental probabilities of isomers compared to theoretical probabilities should be attributed to thermodynamic control.

The Emergence of Multiple Coordination Numbers in Gold–Cyanoarene Complexes: A Study of the On-Surface Coordination Mechanism

“…These coordination bonds originate from the 5d orbital electrons of the gold atom. On-surface coordination has been studied with various d-block metals, including Au, Co, Cu, and Fe, and ligands containing such functional groups as cyano, isocyano, pyridyl, or carboxy that form coordination bonds − that differ from those produced in solution chemistry. , For example, a threefold coordination to d-block metal is typically encountered on surfaces − ,, but not in solution. There have been several attempts to elucidate the oxidation states of metal–organic complexes formed by on-surface chemical reactions, − but the charge states and energy levels of the central metal and ligands with respect to the coordination number still remain unclear in these cases.…”

Structural and anionic effects of microcrystalline Zn-CPs on 4-nitrophenol sensing performances

“…a dichloromethane solution of L (Table 1). The crystal structure of [ZnL 3 ] n (BF 4 ) 2n was built as a pcu net (point symbol 4 12 6 3 ) showing 3-fold interpenetrated frameworks (Fig. 1a).…”

“…A self-assembly process between metal cations and electrondonor ligands allows for construction of coordination compounds and introduction of functions at the molecular level. [1][2][3] Network structures by control of building blocks and relatively large voids usually have been reported as resulting in metal-organic frameworks (MOFs) and coordination polymers (CPs) boasting the structural advantages such as high thermal stability, molecular rigidity, and specic hydrophilicity of voids. 4 Many research groups have reported useful coordination compounds for gas adsorption, 5 chiral molecule detection, 6 and catalysis.…”

Self-Assembly of Metallo-Supramolecules with Dissymmetrical Ligands and Characterization by Scanning Tunneling Microscopy

“…Therefore, effective characterization techniques are highly demanded for investigating the supramolecules with dissymmetrical ligands. In recent years, scanning tunneling microscopy (STM) has emerged as a powerful tool to characterize supramolecular assemblies, since it can directly image each individual structure at submolecular resolution and reflect the population of each isomer in the complex system …”