Name: synthesis and characterization of functionalized metal-organic frameworks
Uploaded: 2014-09-05T15:45:00
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This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award DE-FG02-12ER16362.

1. Synthesis of the Parent MOF (Br-YOMOF)
<ol>
	<li>Weigh out 50 mg Zn(NO3)2 &#215; 6 H2O (0.17 mmol), 37.8 mg dpni (0.09 mmol) and 64.5 mg 1,4-dibromo-2,3,5,6-tetrakis-(4-carboxyphenyl)benzene (Br-tcpb, 0.09 mmol). Combine all solid ingredients in a 4-dram vial.</li>
	<li>Add 10 ml of DMF measured with a graduated cylinder to the vial with the solid ingredients. Then, using a 9&#8217;&#8217; Pasteur pipet, add one drop (0.05 ml) of concentrated HCl (CA...

<ol>
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Mater. 25, 739-744 (2013).</li><li>Karagiaridi, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Opening+Metal&#8211;Organic+Frameworks+Vol.+2:+Inserting+Longer+Pillars+into+Pillared-Paddlewheel+Structures+through+Solvent-Assisted+Linker+Exchange.">Opening Metal&#8211;Organic Frameworks Vol. 2: Inserting Longer Pillars into Pillared-Paddlewheel Structures through Solvent-Assisted Linker Exchange.</a> Chem. Mater. 25, 3499-3503 (2013).</li><li>Li, T., Kozlowski, M. T., Doud, E. A., Blakely, M. N., Rosi, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stepwise+Ligand+Exchange+for+the+Preparation+of+a+Family+of+Mesoporous+MOFs.">Stepwise Ligand Exchange for the Preparation of a Family of Mesoporous MOFs.</a> J. Am. Chem. 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MOF crystallization is a delicate procedure that can be inhibited by even slight variations in the multiple parameters that describe the synthetic conditions. Therefore, special care needs to be taken when preparing the reaction mixture. The purity of the organic linkers should be confirmed by 1H NMR prior to the onset of the synthesis, as the presence of even small amounts of impurities is known to prevent crystallization altogether or result in the formation of undesired crystalline products. Polar, high-boi...

Metal-organic frameworks (MOFs) are a class of crystalline coordination polymers consisting of metal-based nodes (e.g., Zn2+, Zn4O6+, Zr6O4(OH)412+, Cr3(H2O)2OF6+, Zn2(COO)4) connected by organic linkers (e.g., di-, tri-, tetra- and hexacarboxylates, imidazolates1, dipyridyls; see Figure 1).2 Their highly ordered (and thus amenable to high levels of characterization) structures, combined with their exceptional surface areas (reaching 7,000 m2/g)3 endow them with the potential as attractive candidates for a slew of applications, ranging from hydrogen storage4 and carbon capture5,6 to catalysis,7,8 sensing9,10 and light harvesting.11 Not surprisingly, MOFs have elicited a great amount of interest in the science and materials engineering communities; the number of publications on MOFs in peer-reviewed journals has been increasing exponentially over the past decade, with 1,000-1,500 articles currently being published per year.
The synthesis of MOFs with desirable properties, however, poses a series of challenges. Their principal point of attraction, namely their exceptional porosity, in fact may present, for specific MOFs, one of the greatest obstacles towards their successful development. The large empty space present within the frameworks of these materials detracts from their thermodynamic stability; as a result, when MOFs are synthesized de novo (i.e., by solvothermally reacting the metal precursors and organic linkers in one step), their constituent building blocks often tend to assemble into denser, less-porous (and less desirable for some applications such as gas storage) analogues.12 After the procedure to reproducibly obtain the framework of desirable topology has been developed, the MOF needs to be treated in order to enable its application in processes that require gas sorption. Since MOFs are synthesized in a solution, the cages and channels of the newly grown MOF crystals are typically full of the high-boiling solvent used as the reaction medium; the removal of the solvent without inducing the collapse of the framework under the capillary forces requires a series of specialized procedures known as &#8220;MOF activation&#8221;.13 Finally, to ensure the purity of the end product and to enable conclusive studies of fundamental properties, MOFs need to be rigorously characterized upon their synthesis. Given the fact that MOFs are coordination polymers, which are highly insoluble in conventional solvents, this process often involves several techniques developed especially for this class of materials. Many of these techniques rely on X-ray diffraction (XRD), which is uniquely suited to provide high-level characterization of these crystalline materials.
Typically, MOF synthesis in the so-called de novo fashion employs one-pot solvothermal reactions between the metal precursors (inorganic salts) and the organic linkers. This method suffers from multiple limitations, as there is little control over the arrangement of the MOF components into the framework, and the resulting product does not always possess the desired topology. An easy to implement approach that allows circumventing the problems associated with the de novo MOF synthesis is solvent-assisted linker exchange (SALE, Figure 2).14-16 This method involves exposing easily obtainable MOF crystals to a concentrated solution of the desired linker, until the daughter linkers completely replace those of the parent. The reaction proceeds in a single crystal-to-single crystal fashion &#8212; that is, despite the replacement of the linkers within the framework, the material retains the topology of the original parent MOF. SALE essentially allows synthesis of MOFs with linker-topology combinations that are difficult to access de novo. So far, this method has been successfully implemented to overcome various synthetic MOF challenges, such as control over catenation,17 expansion of MOF cages,18,19 synthesis of high energy polymorphs20, development of catalytically active materials20,21 and site-isolation to protect reactive reagents.22
Freshly synthesized MOFs almost always have channels filled with the solvent used during their synthesis. This solvent needs to be removed from the frameworks in order to take advantage of their gas sorption properties. Conventionally, this is achieved by a) exchanging the solvent in the channels (usually a high boiling solvent like N,N&#8217;-dimethylformamide, DMF) with a more volatile solvent like ethanol or dichloromethane by soaking the MOF crystals in the solvent of choice, b) heating the MOF crystals under vacuum for prolonged times to evacuate the solvent, or c) a combination of these two techniques. These activation methods are, however, not suitable for many of the high-surface thermodynamically fragile MOFs that may suffer from framework collapse under such harsh conditions. A technique that allows solvent removal from the cages of the MOF, while avoiding the onset of extensive framework collapse, is activation through supercritical CO2 drying.23 During this procedure, the solvent inside the MOF structure is replaced with liquid CO2. The CO2 is subsequently heated and pressurized past its supercritical point, and eventually allowed to evaporate from the framework. Since supercritical CO2 does not possess capillary forces, this activation treatment is less forcing than conventional vacuum heating of MOFs, and has enabled access to most of the ultrahigh Brunauer-Emmett-Teller (BET) surface areas that have been published so far, including the MOF with the champion surface area.3,24,25
In this paper, we describe the de novo synthesis of a representative easily accessible MOF that serves as a good template for SALE reactions &#8212; the pillared-paddlewheel framework Br-YOMOF.26 Its long and relatively weakly bound N,N&#8217;-di-4-pyridylnaphthalenetetracarboxydiimide (dpni) pillars can be readily exchanged with meso-1,2-di(4-pyridyl)-1,2-ethanediol (dped) to produce an isostructural MOF SALEM-5 (Figure 2).18 Furthermore, we outline the steps that need to be taken to activate SALEM-5 by supercritical CO2 drying and to successfully collect its N2 isotherm and obtain its BET surface area. We also describe various techniques pertinent to MOF characterization, such as X-ray crystallography and 1H NMR spectroscopy (NMR).

<table border="0" cellpadding="0" cellspacing="0" width="352">
	<tbody>
		<tr height="64">
			<td height="64" style="height:64px;width:88px;">Name of Material/ Equipment</td>
			<td style="width:88px;">Company</td>
			<td style="width:88px;">Catalog number</td>
			<td style="width:88px;">Comments/Description</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">6&#8217;&#8217; Pasteur pipet</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">14673-010</td>
			<td style="width:88px;">For transferring MOF crystals</td>
		</tr>
		<tr height="127">
			<td height="127" style="height:127px;width:88px;">9&#8217;&#8217; Pasteur pipet</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">14673-043</td>
			<td style="width:88px;">For separating liquid solution from MOF crystals</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">1-dram vials</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;"></td>
			<td style="width:88px;">For preparation of NMR samples</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:88px;">2-dram vials</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">66011-088</td>
			<td style="width:88px;">For small-scale SALE reactions</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:88px;">4-dram vials</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">66011-121</td>
			<td style="width:88px;">For de novo pillared-paddlewheel MOF synthesis</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:88px;">NMR tube Grade 7</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">897235-0000</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">NMR instrument Avance III 500 MHz</td>
			<td style="width:88px;">Bruker</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">Oven</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">414004-566</td>
			<td style="width:88px;">For solvothermal MOF reactions</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:88px;">Sonicator</td>
			<td style="width:88px;">Branson</td>
			<td style="width:88px;">3510-DTH</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:88px;">Balance</td>
			<td style="width:88px;">Mettler-Toledo</td>
			<td style="width:88px;">XS104</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="78">
			<td height="100" rowspan="2" style="height:101px;width:88px;">Superctitical CO2 dryer</td>
			<td rowspan="2" style="width:88px;">Tousimis&#8482; Samdri&#174;</td>
			<td rowspan="2" style="width:88px;">8755B</td>
			<td rowspan="2" style="width:88px;">For activation of pillared-paddlewheel MOFs</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:88px;">Activation dish</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:88px;">Tristar II 3020</td>
			<td style="width:88px;">Micromeritics</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;">For collection of gas isotherms/measurement of BET surface area</td>
		</tr>
		<tr height="211">
			<td height="211" style="height:211px;width:88px;">X-ray diffractometer</td>
			<td style="width:88px;">Bruker</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;">Kappa geometry goniometer, CuK&#945; radiation and Powder-diffraction data collection plugin.</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:88px;">Capillary tubes</td>
			<td style="width:88px;">Charles-Supper</td>
			<td style="width:88px;">Boron-Rich BG07&#160;</td>
			<td style="width:88px;">Thin walled Boron Rich capillary 0.7mm diameter</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">Beeswax</td>
			<td style="width:88px;">Huber</td>
			<td style="width:88px;">WAX</td>
			<td style="width:88px;">sticky wax for specimen fixation</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:88px;">Modeling Clay</td>
			<td style="width:88px;">Van Aken</td>
			<td style="width:88px;">Plastalina</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:88px;">CO2 (l)</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:88px;">N2 (l)</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:88px;">N2 (g)</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;">N/A</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:88px;">DMF</td>
			<td style="width:88px;">VWR</td>
			<td style="width:88px;">MK492908</td>
			<td style="width:88px;">For MOF reactions and storage</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:88px;">Ethanol</td>
			<td style="width:88px;">Sigma-Aldrich</td>
			<td style="width:88px;">459844</td>
			<td style="width:88px;">For solvent exchange before supercritical drying</td>
		</tr>
		<tr height="51">
			<td height="51" style="height:51px;width:88px;">Zn(NO3)2 &#215; 6 H2O</td>
			<td style="width:88px;">Fluka</td>
			<td style="width:88px;">96482</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:88px;">dped</td>
			<td style="width:88px;">TCI</td>
			<td style="width:88px;">D0936</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">dpni</td>
			<td style="width:88px;"></td>
			<td style="width:88px;"></td>
			<td style="width:88px;">Synthesized according to a published procedure</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:88px;">Br-tcpb</td>
			<td style="width:88px;"></td>
			<td style="width:88px;"></td>
			<td style="width:88px;">Synthesized according to a published procedure</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:88px;">D2SO4</td>
			<td style="width:88px;">Cambridge Isotopes</td>
			<td style="width:88px;">DLM-33-50</td>
			<td style="width:88px;">For MOF NMR</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:88px;">d6-DMSO</td>
			<td style="width:88px;">Cambridge Isotopes</td>
			<td style="width:88px;">DLM-10-100</td>
			<td style="width:88px;">For MOF NMR</td>
		</tr>
	</tbody>
</table>

synthesis and characterization of functionalized metal-organic frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

The use of HCl during MOF synthesis is often beneficial for the growth of high quality MOF crystals. As it slows down the deprotonation of the carboxylate (and the binding of the linkers to the metal centers), it promotes growth of larger crystals and prevents formation of amorphous and polycrystalline phases, which may form if the reaction is allowed to proceed more rapidly. In fact, as it can be seen in Figure 3, the pillared-paddlewheel MOFs that are produced during this reaction form large, yellow cr...

Watch this Scientific Journal Video about Synthesis and Characterization of Functionalized Metal-organic Frameworks at JoVE.com

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Research

JoVE Journal

Chemistry

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

Synthesis of Low-Valent MOFs from Multitopic Phosphine Linkers

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Author Spotlight: Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers  

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...

Magnetometric Characterization of Redox-Active MOFs Solid-State Electrochemistry

Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks  

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs ...

Triazole and Tetrazole Functionalized Zr-MOFs Synthesis and Characterization

Synthesis of Triazole and Tetrazole-Functionalized Zr-Based Metal-Organic Frameworks Through Post-Synthetic Ligand Exchange

Author Spotlight: Functionalizing Metal-Organic Frameworks: Advancements, Challenges, and the Power of Post-Synthetic Ligand Exchange 

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. ...