On-Surface Fabrication of Bimetallic Metal–Organic Frameworks through the Synergy and Competition among Noncovalent Interactions

Abstract

Two-dimensional metal–organic frameworks (2D-MOFs) are attracting more attention due to their unique properties. Various 2D-MOF structures have been fabricated on surfaces in which either only one kind of metal was incorporated or only one kind of noncovalent interaction was involved in a bimetallic network. However, 2D-MOFs involving different kinds of noncovalent interactions and multiple metal components are more complex and less predictable. Here, we choose the uracil (U) molecule together with alkali metals [sodium (Na) and cesium (Cs)] and a transition metal [iron (Fe)] as model systems and successfully construct two kinds of bimetallic 2D-MOFs through the synergy and competition among noncovalent interactions, which is revealed by the high-resolution scanning tunneling microscopy imaging and density functional theory calculations. Such a systematic study may help to improve our fundamental understanding of the interaction mechanism of noncovalent bonds and, moreover, lead to further investigations of the unprecedented functions of surface-supported 2D-MOF structures.

Flexible Alkali–Halogen Bonding in Two Dimensional Alkali-Metal Organic Frameworks

“…Previous reports have shown that alkali atoms deposited on Au(111) generally lose their valence electrons to the substrates. 14,15,28 In this case, we performed the Bader charge analysis and obtained the valence of the sodium as +0.86, confirming that the sodium atoms exist in the form of Na + ions. Due to the low electron density and low height profile, Na ions has a weak contrast in conventional STM images.…”

“…In this aspect, one would expect even higher flexibility in MOFs consisting of alkali ions and organic molecules since alkali ions are highly isotropic compared to all transition metal ions. There have been some reports on surface supported 2D metal–organic layers containing alkali ions. − However, the capability of constructing flexible 2D MOFs with alkali ions has not been demonstrated. This requires precise control over the bonding geometry between the organic nucleophilic group and alkali metal ion, so that the coordination nodes can have identical coordination number while still having considerable flexibility.…”

Construction and Structural Transformation of Metal–Organic Nanostructures Induced by Alkali Metals and Alkali Metal Salts

“…Metal–organic nanostructures, consisting of metal nodes and organic ligands, make up a class of structurally diverse and functionally tunable materials , and have proven to be versatile platforms in a wide range of scientific fields, including biomedicine, energy harvesting, and catalysis. , In an effort to achieve tailored properties and the desired performance, different types of metals have been integrated to regulate fundamental chemical interactions within building blocks, which range from transition metals to alkali and alkaline earth metals. − It has also aroused considerable interest in the surface science community; meanwhile, surface science techniques allow direct visualization of metal–organic nanostructures supported by solid surfaces in real space and determination of the intermolecular interactions involved. Tremendous effort has been devoted to the engineering of low-dimensional metal–organic architectures on surfaces mainly based on directional coordination bonds with d-block transition metals embedded, − as well as flexible coordination provided by f-block lanthanides. − Recently, alkali metals derived from either pure alkali metals − or alkali halides (e.g., NaCl and KBr) − have been introduced to interact with organic molecules on surfaces via isotropic electrostatic ionic bonding, enabling the structural diversity of metal–organic nanostructures. , In these cases, both pure alkali metals and alkali metal salts are applied to provide metal centers. However, their differences in the construction of alkali-based metal–organic nanostructures as alkali metal providers have been less discussed, and the corresponding influence on the structural diversity remains elusive.…”

Chiral and Catalytic Effects of Site-Specific Molecular Adsorption

“…and the intermolecular interactions . These factors play a fundamental role in self-assembly and the bottom-up growth techniques for producing macromolecular systems − and molecular structures with various geometries ,− and chirality. ,,,,− These arrangements are of high interest for applications in molecular electronics, ,,,,,− optoelectronics, − adsorption-induced molecular magnetism, − as well as molecular surface chemistry and catalysis. ,, …”