Proximity Effect in Crystalline Framework Materials: Stacking-Induced Functionality in MOFs and COFs

<div>Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) consist of molecular building blocks being stitched together by strong bonds. They are well known for their porosity, large surface area, and related properties. The electronic properties of most MOFs and COFs are the superposition of those of their constituting building blocks. If crystalline, however, solid-state phenomena can be observed, such as electrical conductivity, substantial dispersion of electronic bands, broadened absorption bands, formation of excimer states, mobile charge carriers, and indirect band gaps. These effects emerge often by the proximity effect caused by the van-der-Waals interactions between stacked aromatic building blocks. This Progress Report shows how functionality is imposed by this proximity effect, that is, by stacking aromatic molecules in such a way that extraordinary electronic and optoelectronic properties emerge in MOFs and COFs. After discussing the proximity effect in graphene-related materials, its importance for layered COFs and MOFs is shown. For MOFs with well-defined structure, the stacks of aromatic building blocks can be controlled via varying MOF topology, lattice constant, and by attaching steric control units. Finally, an overview of theoretical methods to predict and analyze these effects is given, before the layer-by-layer growth technique for well-ordered surface-mounted MOFs is summarized.</div>

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Proximity Effect in Crystalline Framework Materials: Stacking-Induced Functionality in MOFs and COFs

10.26434/chemrxiv.9912812 ◽

2019 ◽

Author(s):

Agnieszka Kuc ◽

Maximilian Springer ◽

Kamal Batra ◽

Rosalba Juarez-Mosqueda ◽

Christof Wöll ◽

...

Keyword(s):

Proximity Effect ◽

Building Blocks ◽

Layer Growth ◽

Van Der Waals Interactions ◽

Layer By Layer ◽

Absorption Bands ◽

Framework Materials ◽

Molecular Building Blocks ◽

Control Units ◽

Metal Organic

<div>Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) consist of molecular building blocks being stitched together by strong bonds. They are well known for their porosity, large surface area, and related properties. The electronic properties of most MOFs and COFs are the superposition of those of their constituting building blocks. If crystalline, however, solid-state phenomena can be observed, such as electrical conductivity, substantial dispersion of electronic bands, broadened absorption bands, formation of excimer states, mobile charge carriers, and indirect band gaps. These effects emerge often by the proximity effect caused by the van-der-Waals interactions between stacked aromatic building blocks. This Progress Report shows how functionality is imposed by this proximity effect, that is, by stacking aromatic molecules in such a way that extraordinary electronic and optoelectronic properties emerge in MOFs and COFs. After discussing the proximity effect in graphene-related materials, its importance for layered COFs and MOFs is shown. For MOFs with well-defined structure, the stacks of aromatic building blocks can be controlled via varying MOF topology, lattice constant, and by attaching steric control units. Finally, an overview of theoretical methods to predict and analyze these effects is given, before the layer-by-layer growth technique for well-ordered surface-mounted MOFs is summarized.</div>

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Modeling the Layer-by-Layer Growth of HKUST-1 Metal-Organic Framework Thin Films

Nanomaterials ◽

10.3390/nano11071631 ◽

2021 ◽

Vol 11 (7) ◽

pp. 1631

Author(s):

Qiang Zhang ◽

Yohanes Pramudya ◽

Wolfgang Wenzel ◽

Christof Wöll

Keyword(s):

Thin Films ◽

Surface Roughness ◽

Deposition Rate ◽

Layer Growth ◽

Coarse Grained ◽

Structural Defects ◽

Effect Of Temperature ◽

Layer By Layer ◽

Reactant Concentration ◽

Metal Organic

Metal organic frameworks have emerged as an important new class of materials with many applications, such as sensing, gas separation, drug delivery. In many cases, their performance is limited by structural defects, including vacancies and domain boundaries. In the case of MOF thin films, surface roughness can also have a pronounced influence on MOF-based device properties. Presently, there is little systematic knowledge about optimal growth conditions with regard to optimal morphologies for specific applications. In this work, we simulate the layer-by-layer (LbL) growth of the HKUST-1 MOF as a function of temperature and reactant concentration using a coarse-grained model that permits detailed insights into the growth mechanism. This model helps to understand the morphological features of HKUST-1 grown under different conditions and can be used to predict and optimize the temperature for the purpose of controlling the crystal quality and yield. It was found that reactant concentration affects the mass deposition rate, while its effect on the crystallinity of the generated HKUST-1 film is less pronounced. In addition, the effect of temperature on the surface roughness of the film can be divided into three regimes. Temperatures in the range from 10 to 129 °C allow better control of surface roughness and film thickness, while film growth in the range of 129 to 182 °C is characterized by a lower mass deposition rate per cycle and rougher surfaces. Finally, for T larger than 182 °C, the film grows slower, but in a smooth fashion. Furthermore, the potential effect of temperature on the crystallinity of LbL-grown HKUST-1 was quantified. To obtain high crystallinity, the operating temperature should preferably not exceed 57 °C, with an optimum around 28 °C, which agrees with experimental observations.

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Epitaxial Solid-Solution Films of Immiscible MgO and CaO

MRS Proceedings ◽

10.1557/proc-341-127 ◽

1994 ◽

Vol 341 ◽

Cited By ~ 1

Author(s):

E. S. Hellman ◽

E. H. Hartford

Keyword(s):

Solid Solution ◽

Molecular Beam Epitaxy ◽

Lattice Constant ◽

Solid Solutions ◽

Molecular Beam ◽

Building Blocks ◽

Layer Growth ◽

Growth Mode ◽

Miscibility Gap ◽

Layer By Layer

AbstractMetastable solid-solutions in the MgO-CaO system grow readily on MgO at 300°C by molecular beam epitaxy. We observe RHEED oscillations indicating a layer-by-layer growth mode; in-plane orientation can be described by the Matthews theory of island rotations. Although some films start to unmix at 500°C, others have been observed to be stable up to 900°C. The Mgl-xCaxO solid solutions grow despite a larger miscibility gap in this system than in any system for which epitaxial solid solutions have been grown. We describe attempts to use these materials as adjustable-lattice constant epitaxial building blocks

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A Molecular Artisans Guide to Supramolecular Coordination Complexes and Metal Organic Frameworks

Journal of Molecular and Engineering Materials ◽

10.1142/s2251237315400043 ◽

2015 ◽

Vol 03 (01n02) ◽

pp. 1540004 ◽

Cited By ~ 2

Author(s):

Xialu Wu ◽

David J. Young ◽

T. S. Andy Hor

Keyword(s):

Chemical Reactivity ◽

Metal Organic Frameworks ◽

Building Blocks ◽

Coordination Complexes ◽

Large Molecules ◽

Molecular Building Blocks ◽

Supramolecular Coordination ◽

Metal Organic ◽

Molecular Synthesis ◽

And Function

As molecular synthesis advances, we are beginning to learn control of not only the chemical reactivity (and function) of molecules, but also of their interactions with other molecules. It is this basic idea that has led to the current explosion of supramolecular science and engineering. Parallel to this development, chemists have been actively pursuing the design of very large molecules using basic molecular building blocks. Herein, we review the general development of supramolecular chemistry and particularly of two new branches: supramolecular coordination complexes (SCCs) and metal organic frameworks (MOFs). These two fields are discussed in detail with typical examples to illustrate what is now possible and what challenges lie ahead for tomorrow's molecular artisans.

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Inverse Design of Nanoporous Crystalline Reticular Materials with Deep Generative Models

10.26434/chemrxiv.12186681.v1 ◽

2020 ◽

Cited By ~ 3

Author(s):

Zhenpeng Yao ◽

Benjamin Sanchez-Lengeling ◽

N. Scott Bobbitt ◽

Benjamin J. Bucior ◽

Sai Govind Hari Kumar ◽

...

Keyword(s):

Self Assembly ◽

Metal Organic Framework ◽

Internal Surface ◽

Building Blocks ◽

Structural Features ◽

Generative Models ◽

Combinatorial Design ◽

Surface Areas ◽

Molecular Building Blocks ◽

Metal Organic

Reticular frameworks are crystalline porous materials that form <i>via</i> the self-assembly of molecular building blocks (<i>i.e.</i>, nodes and linkers) in different topologies. Many of them have high internal surface areas and other desirable properties for gas storage, separation, and other applications. The notable variety of the possible building blocks and the diverse ways they can be assembled endow reticular frameworks with a near-infinite combinatorial design space, making reticular chemistry both promising and challenging for prospective materials design. Here, we propose an automated nanoporous materials discovery platform powered by a supramolecular variational autoencoder (SmVAE) for the generative design of reticular materials with desired functions. We demonstrate the automated design process with a class of metal-organic framework (MOF) structures and the goal of separating CO<sub>2</sub> from natural gas or flue gas. Our model exhibits high fidelity in capturing structural features and reconstructing MOF structures. We show that the autoencoder has a promising optimization capability when jointly trained with multiple top adsorbent candidates identified for superior gas separation. MOFs discovered here are strongly competitive against some of the best-performing MOFs/zeolites ever reported. This platform lays the groundwork for the design of reticular frameworks for desired applications.

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Inverse Design of Nanoporous Crystalline Reticular Materials with Deep Generative Models

10.26434/chemrxiv.12186681 ◽

2020 ◽

Author(s):

Zhenpeng Yao ◽

Benjamin Sanchez-Lengeling ◽

N. Scott Bobbitt ◽

Benjamin J. Bucior ◽

Sai Govind Hari Kumar ◽

...

Keyword(s):

Self Assembly ◽

Metal Organic Framework ◽

Internal Surface ◽

Building Blocks ◽

Structural Features ◽

Generative Models ◽

Combinatorial Design ◽

Surface Areas ◽

Molecular Building Blocks ◽

Metal Organic

Reticular frameworks are crystalline porous materials that form <i>via</i> the self-assembly of molecular building blocks (<i>i.e.</i>, nodes and linkers) in different topologies. Many of them have high internal surface areas and other desirable properties for gas storage, separation, and other applications. The notable variety of the possible building blocks and the diverse ways they can be assembled endow reticular frameworks with a near-infinite combinatorial design space, making reticular chemistry both promising and challenging for prospective materials design. Here, we propose an automated nanoporous materials discovery platform powered by a supramolecular variational autoencoder (SmVAE) for the generative design of reticular materials with desired functions. We demonstrate the automated design process with a class of metal-organic framework (MOF) structures and the goal of separating CO<sub>2</sub> from natural gas or flue gas. Our model exhibits high fidelity in capturing structural features and reconstructing MOF structures. We show that the autoencoder has a promising optimization capability when jointly trained with multiple top adsorbent candidates identified for superior gas separation. MOFs discovered here are strongly competitive against some of the best-performing MOFs/zeolites ever reported. This platform lays the groundwork for the design of reticular frameworks for desired applications.

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Stepwise Transformation of the Molecular Building Blocks in a Porphyrin-Encapsulating Metal–Organic Material

Journal of the American Chemical Society ◽

10.1021/ja4015666 ◽

2013 ◽

Vol 135 (16) ◽

pp. 5982-5985 ◽

Cited By ~ 84

Author(s):

Zhenjie Zhang ◽

Lukasz Wojtas ◽

Mohamed Eddaoudi ◽

Michael J. Zaworotko

Keyword(s):

Organic Material ◽

Building Blocks ◽

Molecular Building Blocks ◽

Metal Organic

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Metal-organic framework (MOF) composites for photodegradation of hazardous organic materials

Journal of Photocatalysis ◽

10.2174/2665976x02666210612042825 ◽

2021 ◽

Vol 02 ◽

Author(s):

Xinxin Liu ◽

Jiaqing Ren ◽

Jiaqi Fang ◽

An Pan ◽

Nianqiao Qin ◽

...

Keyword(s):

Photocatalytic Degradation ◽

Organic Pollutants ◽

Metal Organic Framework ◽

Stable Process ◽

Layer Growth ◽

Thermal Method ◽

Layer By Layer ◽

Wide Range ◽

Metal Organic ◽

Organic Framework

: Photocatalytic degradation is an energy-efficient, cost-effective, and stable process that has a wide-range of applications. It is considered a promising method for the removal of organic pollutants. As a new type of porous materials, Metal-organic framework (MOF) composites have been proven to be an ideal catalyst for the degradation of organic pollutants due to their small size and large specific surface area. In this review, several common preparation methods of MOF composites are evaluated：microwave synthesis, solvent-thermal method, electrochemical method and layer by layer growth method. The degradation effects of MOF composites on different organic pollutants are summarized, and the excellent photocatalytic performances of some MOF composites are demonstrated. Finally, the prospect of photocatalytic degradation of organic pollutants by MOF composites is examined, and the challenges of further development of MOF composites are discussed.

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