Metal-organic Networks Research Articles

Ligation of Carbon Monoxide at Cobalt Single-Metal-Atom Sites in a Surface-Confined Metal–Organic Network: Oxidation State, Anharmonicity, and Long-Range Lateral Interactions

Ligation of Carbon Monoxide at Cobalt Single-Metal-Atom Sites in a Surface-Confined Metal–Organic Network: Oxidation State, Anharmonicity, and Long-Range Lateral Interactions

Transparent and high-porosity aluminum alkoxide network-forming glasses

Metal-organic network-forming glasses are an emerging type of material capable of combining the modular design and high porosity of metal-organic frameworks and the high processability and optical transparency of glasses. However, a generalizable strategy for achieving both high porosity and high glass-forming ability in modularly designed metal-organic networks has yet to be developed. Herein, we develop a series of aluminum alkoxide glasses and monoliths by linking aluminum-oxo clusters with alcohol linkers. A bulky monodentate alcohol modulator is introduced during synthesis and act as both network plasticizer and pore template, which can be removed by the subsequent solvent exchange to give gas accessible pores. Glasses synthesized with the modulator template exhibit well-defined glass transitions in their as-synthesized form and high surface areas up to 500 m2/g after activation, making them among the most porous glassy materials. The aluminum alkoxide glasses also have optical transparency and fluorescent properties, and their structures are elucidated by pair-distribution functions, spectroscopic and compositional analysis. These findings could significantly expand the library of microporous metal-organic network-forming glasses and enable their future applications.

Co(III), Co(II), Co(I): Tuning Single Cobalt Metal Atom Oxidation States in a 2D Coordination Network

AbstractIt is shown that the self‐assembly of a surface‐confined metal–organic network such as cobalt porphyrins on graphene is accompanied by the evolution of coordination‐dependent observables in the electronic structure: variation of the layer's valence states within almost 1 eV range and of the metal atoms oxidation states. Coordination of cobalt porphyrins, driven by Co ad‐atoms, allows the synthesis of single metal atom centers with +3, +2, or +1 oxidation states. The electronic structure is determined by lateral interactions extending up to a few nanometers, beyond nearest‐neighbor distances. The reactivity of the single Co sites, which is strongly dependent on the local electronic configuration and, thus, on the metal‐specific oxidation state, is probed by carbon monoxide, which is found to ligate at pyridinic Co(I) at room temperature for background pressures above a fraction of a mbar.

Physical confinement versus adsorption driven reconstruction: The case of sulfate anion interaction with vicinal Cu(111) surfaces

Nano-electrochemistry, i.e., the research of the properties of nano-(structured) electrodes and their influence on electrochemical processes when immersed inside an electrolyte, represents a hot topic in view of applications in nano-electronics, electro-catalysis and energy storage devices. The role of physical confinement in the electrochemical fabrication and performances of the respective systems have been recently addressed in the context of metal-organic networks on surfaces, but rarely of nano-structured bare metal surfaces, for instance, regularly stepped (vicinal) surfaces. In this work we investigate the interplay between physical confinement and adsorbate induced restructuring by the electrochemical adsorption of sulfate anions on the flat and two distinctly different vicinal Cu(111) surfaces. Sulfate adsorption on the flat Cu(111) surface is known to create a long-range ordered Moiré-superstructure with lattice parameters in the 2–4 nm range due to an expansion of the topmost layer of copper atoms with respect to the underlying crystal planes. This restructuring is also observed on a vicinal Cu(111) surface whose original terrace width is considerably smaller than the lattice vectors of the sulfate induced Moiré-structure. The results clearly indicate not only that the Moiré formation lifts the physical confinement imposed by the initial terrace width, but also shine more light on the Moiré formation process itself. Such adsorbate induced restructuring, of course, depends on the respective adsorbate – electrode combination, but must, in principle, always be taken into account in order to understand electrochemical processes at nano-structured (and nano-sized) electrode surfaces.

Transmetalation in Surface-Confined Single-Layer Organometallic Networks with Alkynyl-Metal-Alkynyl Linkages.

Transmetalation represents an appealing strategy toward fabricating and tuning functional metal-organic polymers and frameworks for diverse applications. In particular, building two-dimensional metal-organic and organometallic networks affords versatile nanoarchitectures of potential interest for nanodevices and quantum technology. The controlled replacement of embedded metal centers holds promise for exploring versatile material varieties by serial modification and different functionalization. Herein, we introduce a protocol for the modification of a single-layer carbon-metal-based organometallic network via transmetalation. By integrating external Cu atoms into the alkynyl-Ag organometallic network constructed with 1,3,5-triethynylbenzene precursors, we successfully realized in situ its highly regular alkynyl-Cu counterpart on the Ag(111) surface. While maintaining a similar lattice periodicity and pore morphology to the original alkynyl-Ag sheet, the Cu-based network exhibits increased thermal stability, guaranteeing improved robustness for practical implementation.

Element-specific cluster growth on the two-dimensional metal–organic network

A porous two-dimensional metal–organic network (2D-MON) on a substrate captures deposited metal atoms and metal clusters growing in the pores of the 2D-MON. We found that the growth mechanisms of Ag, In, and Pd clusters in the 2D-MON synthesized from 1,3,5-tris(4-bromophenyl)benzene molecules on Ag(111) are different from each other, and the difference derives from the interaction of an adatom with the 2D-MON. Ag and Pd clusters grow from the 2D-MON since the interaction of Ag and Pd adatoms with the 2D-MON is attractive. In clusters grow inside of the pores of the 2D-MON since the interaction between an In adatom and the 2D-MON is repulsive. The growth process of metal clusters is determined by the element-specific behavior of metal adatoms in the pores, taking into account interactions with the 2D-MON.

Construction of Two-Dimensional Organometallic Coordination Networks with Both Organic Kagome and Semiregular Metal Lattices on Au(111).

Two-dimensional metal-organic networks (2D MONs) having heterogeneous coordination nodes (HCNs) could exhibit excellent performance in catalysis and optoelectronics because of the unbalanced electron distribution of the coordinating metals. Therefore, the design and construction of 2D MONs with HCNs are highly desirable but remain challenging. Here, we report the construction of 2D organometallic coordination networks with an organic Kagome lattice and a semiregular metal lattice on Au(111) via the in situ formation of HCNs. Using a bifunctional precursor 1,4-dibromo-2,5-diisocyanobenzene, the coordination of isocyano with Au adatom on a room-temperature Au(111) yielded metal-organic coordination chains with isocyano-Au-isocyano nodes. In contrast, on a high-temperature Au(111), a selective debromination/coordination cascade reaction occurred, affording 2D organometallic coordination networks with phenyl-Au-isocyano nodes. By combining scanning tunneling microscopy and density functional theory calculations, we determined the structures of coordination products and the nature of coordination nodes, demonstrating a thermodynamically favorable pathway for forming the phenyl-Au-isocyano nodes.

Unfolding Chemical Diversity: Co-Sublimation in 2D Metal–Organic Networks for the Oxygen Reduction Reaction

Unfolding Chemical Diversity: Co-Sublimation in 2D Metal–Organic Networks for the Oxygen Reduction Reaction

Ferromagnetism on an atom-thick & extended 2D metal-organic coordination network

Ferromagnetism is the collective alignment of atomic spins that retain a net magnetic moment below the Curie temperature, even in the absence of external magnetic fields. Reducing this fundamental property into strictly two-dimensions was proposed in metal-organic coordination networks, but thus far has eluded experimental realization. In this work, we demonstrate that extended, cooperative ferromagnetism is feasible in an atomically thin two-dimensional metal-organic coordination network, despite only ≈ 5% of the monolayer being composed of Fe atoms. The resulting ferromagnetic state exhibits an out-of-plane easy-axis square-like hysteresis loop with large coercive fields over 2 Tesla, significant magnetic anisotropy, and persists up to TC ≈ 35 K. These properties are driven by exchange interactions mainly mediated by the molecular linkers. Our findings resolve a two decade search for ferromagnetism in two-dimensional metal-organic coordination networks.

Solvent control of dimensionality in titanium aryloxide coordination polymers prepared from 4,4′-bis(hydroxyphenyl)sulfide

The crystal and molecular structures of three covalent metal–organic network (CMON) materials synthesized from titanium (IV) isopropoxide and the Bisphenol-A analog 4,4′-bis(hydroxyphenyl)sulfide in three different solvents have been determined. The structures of the one-dimensional chain coordination polymer [trans-Ti(μ-O:O’-OC6H4SC6H4O)2(C5H5N)2]n (1) obtained from pyridine and the two-dimensional sheet coordination polymer {[Ti2(μ-O:O’-OC6H4SC6H4O)2(μ2O:κO’-OC6H4SC6H4O)2(C4H8O)2]∙(C4H8O)y}n (2) from tetrahydrofuran both contain octahedral titanium (IV) coordination geometries, whereas the doubly interpenetrated three-dimensional coordination network [Ti2(μ-O:O’-OC6H4SC6H4O)2(μ2O:κO′-OC6H4SC6H4O)2]n (3) synthesized from benzene contains trigonal bipyramidal titanium (IV). Each material has been characterized by single crystal and powder X-ray diffraction, elemental analysis, and by 1H NMR quench when it contains more than one organic component.

Improving the shape stability and photothermal conversion performance of phase change materials through three-dimensional metal-organic network

In order to improve the shape stability of phase change materials (PCMs) while ensuring excellent thermal energy storage / release and photo-thermal conversion performance, three-dimensional metal-organic network (MON) containing polyethylene glycol (PEG) and graphene oxide (GO) composite phase change gels (PEG/MON-G) were prepared. The morphology, structure and thermal-physical properties of the gels were investigated by various instruments. The results indicated that PEG was embedded in the three-dimensional MON constructed by coordination and hydrogen bonding of zinc ions, phytic acid and Kevlar nanofibers, ensuring the shape stability of PEG/MON-G up to 120 °C within the experimental range. Due to the dynamic fracture and recombination of coordination and hydrogen bonding interactions, the composite PCMs exhibited excellent deformability. The melting and crystallization enthalpy of PEG/MON-G containing 89.5 wt% of PEG were 143.9 J·g−1 and 141.0 J·g−1, respectively. PEG/MON-G also had good thermal reliability, in which the phase transition temperature of the melting process reduced by only 0.1 °C and the enthalpy changed only 1.4% after 200 cycles. In addition, the photo-thermal conversion efficiency of the composite phase change gels reached 74.6%. In conclusion, this study provides a new strategy for preparing the shape-stabilized PCMs.

Magnetic Signature in Graphene Using Adsorbed Metal–Organic Networks

Magnetic Signature in Graphene Using Adsorbed Metal–Organic Networks

Theoretical insights into the interplay between metal-organic and covalent bonding in single-layer molecular networks formed by halogen dissociation.

Synthesis via dehalogenative coupling due to thermal annealing is one of the most common routes of growing metal-organic and covalent polymer networks on catalytic metal surfaces. We present a computational approach taking into account both metal-coordinated and covalent C-C bonding interactions, which drive the self-assembly of tetrabrominated polyarene molecules into single-layer ordered and disordered nanostructures. The proposed coarse-grained lattice model is simulated using the Monte Carlo method. We investigate the annealing effect in ensembles of nearly and fully dehalogenated molecules, accordingly decreasing the concentration of dissociated (chemisorbed) halogen atoms, to account for the desorption process. The results suggest that dissociated halogens may be at least partially responsible for fragmentation of metal-organic networks on the Cu and Au surfaces. The simulations also show that fragmented covalent networks are mostly disordered or characterized by short-range glass-like order, but larger domains of these phases can be obtained after removing the split off Br atoms. We additionally examine the potential formation of fragments with a hybrid structure consisting of oligomer chains linked side-to-side by metal adatoms.

Accurate construction of monolayer, bilayer, sandwich bilayer, four-layer, multi-layer and chiral bilayer 2D pillararene-type supramolecular networks.

The accurate construction of mono-, bi- and multi-layer networks has been an important challenge, especially for bi- and multi-layer networks. Monolayer, bilayer, sandwich bilayer, four-layer, and multi-layer two-dimensional pillararene-type metal-organic coordination networks have been constructed from functionalized pillar[5]arene and pillar[6]arene by utilizing the coordination interaction of cobalt and copper ions and combining with temperature control and guest induction. These two-dimensional coordination networks exhibit the excellent plasticity of pillararenes and structural variety, which are characterized by X-ray single crystal diffraction and PXRD, confirming that pillararenes units can function as excellent tunable scaffolds for structural regulation. Two-dimensional chiral double-layer structure products are also constructed from R- and S-pillar[6]arene, which are obtained by high-performance liquid chromatography. Atomic force microscopic imaging confirms the thicknesses of these networks. Moreover, these networks also exhibit high iodine adsorption capacity in aqueous environments at ambient temperature. The monolayer, bilayer, sandwich bilayer, four-layer and multi-layer structures of the pillararene-type networks represent a new facile supramolecular self-assembly strategy and platform for designing more mono-, bi- and multi-layer two-dimensional nanomaterials and chiral two-dimensional double-layer structures provide a new method for the construction of more two-dimensional chiral polymers.

2D Co-Directed Metal-Organic Networks Featuring Strong Antiferromagnetism and Perpendicular Anisotropy.

Antiferromagnetic spintronics is a rapidly emerging field with the potential to revolutionize the way information is stored and processed. One of the key challenges in this field is the development of novel 2D antiferromagnetic materials. In this paper, the first on-surface synthesis of a Co-directed metal-organic network is reported in which the Co atoms are strongly antiferromagnetically coupled, while featuring a perpendicular magnetic anisotropy. This material is a promising candidate for future antiferromagnetic spintronic devices, as it combines the advantages of 2D and metal-organic chemistry with strong antiferromagnetic order and perpendicular magnetic anisotropy.

Entropy measures of the metal–organic network via topological descriptors

Abstract A family of chemical compounds known as metal–organic networks (MONs) is composed mainly of clusters of metal ions with organic ligands. It can increase volatility or make substances soluble in organic solvents. By using these salient features, organic compounds generate applications in material sciences for sol–gel processing. A graph’s entropy is utilized as a complexity indicator and is interpreted as the structural information content of the graph. Investigating the entropies of relationship systems is a common occurrence in discrete mathematics, computer science, information theory, statistics, chemistry, and biology. In this article, we investigated the degree-based entropies: geometric arithmetic entropy, atom bond connectivity entropy, general Randic′ entropy, and general sum connectivity entropy for MONs. Furthermore, we created tables for all expressions by using 1–10 values for the s s parameter of these entropies.

Designing metal-organic framework fiber network reinforced polymer electrolytes to provide continuous ion transport in solid state lithium metal batteries

Designing metal-organic framework fiber network reinforced polymer electrolytes to provide continuous ion transport in solid state lithium metal batteries

Direct Assembly of Metal-Phenolic Network Nanoparticles for Biomedical Applications.

Coordination assembly offers a versatile means to developing advanced materials for various applications. However, current strategies for assembling metal-organic networks into nanoparticles (NPs) often face challenges such as the use of toxic organic solvents, cytotoxicity because of synthetic organic ligands, and complex synthesis procedures. Herein, we directly assemble metal-organic networks into NPs using metal ions and polyphenols (i.e., metal-phenolic networks (MPNs)) in aqueous solutions without templating or seeding agents. We demonstrate the role of buffers (e.g., phosphate buffer) in governing NP formation and the engineering of the NP physicochemical properties (e.g., tunable sizes from 50 to 270 nm) by altering the assembly conditions. A library of MPN NPs is prepared using natural polyphenols and various metal ions. Diverse functional cargos, including anticancer drugs and proteins with different molecular weights and isoelectric points, are readily loaded within the NPs for various applications (e.g., biocatalysis, therapeutic delivery) by direct mixing, without surface modification, owing to the strong affinity of polyphenols to various guest molecules. This study provides insights into the assembly mechanism of metal-organic complexes into NPs and offers a simple strategy to engineer nanosized materials with desired properties for diverse biotechnological applications.

Order-Disorder Transition of Two-Dimensional Molecular Networks through a Stoichiometric Design.

Materials with disordered structures may exhibit interesting properties. Metal-organic frameworks (MOFs) are a class of hybrid materials composed of metal nodes and coordinating organic linkers. Recently, there has been growing interest in MOFs with structural disorder and the investigations of amorphous structures on surfaces. Herein, we demonstrate a bottom-up method to construct disordered molecular networks on metal surfaces by selecting two organic molecule linkers with the same symmetry but different sizes for preparing two-component samples with different stoichiometric ratios. The amorphous networks are directly imaged by scanning tunneling microscopy under ultrahigh vacuum with a submolecular resolution, allowing us to quantify its degree of disorder and other structural properties. Furthermore, we resort to molecular dynamics simulations to understand the formation of the amorphous metal-organic networks. The results may advance our understanding of the mechanism of formation of monolayer molecular networks with structural disorders, facilitating the design and exploration of amorphous MOF materials with intriguing properties.

Uniform deposition of metal-organic coordination networks on BiVO4 through chemical bonding for efficient solar water splitting

Uniform deposition of metal-organic coordination networks on BiVO4 through chemical bonding for efficient solar water splitting