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>
	<li>Phan, A., 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=Synthesis,+Structure,+and+Carbon+Dioxide+Capture+Properties+of+Zeolitic+Imidazolate+Frameworks.">Synthesis, Structure, and Carbon Dioxide Capture Properties of Zeolitic Imidazolate Frameworks.</a> Acc. Chem. Res. 43, 58-67 (2009).</li><li>Furukawa, H., Cordova, K. E., O&#8217;Keeffe, M., Yaghi, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Chemistry+and+Applications+of+Metal-Organic+Frameworks.">The Chemistry and Applications of Metal-Organic Frameworks.</a> Science. 341, (2013).</li><li>Farha, O. K., 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=Metal&#8211;Organic+Framework+Materials+with+Ultrahigh+Surface+Areas:+Is+the+Sky+the+Limit?.">Metal&#8211;Organic Framework Materials with Ultrahigh Surface Areas: Is the Sky the Limit?.</a> J. Am. Chem. Soc. 134, 15016-15021 (2012).</li><li>Suh, M. P., Park, H. J., Prasad, T. K., Lim, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+Storage+in+Metal&#8211;Organic+Frameworks.">Hydrogen Storage in Metal&#8211;Organic Frameworks.</a> Chem. Rev. 112, 782-835 (2011).</li><li>Sumida, K., 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=Carbon+Dioxide+Capture+in+Metal&#8211;Organic+Frameworks.">Carbon Dioxide Capture in Metal&#8211;Organic Frameworks.</a> Chem. Rev. 112, 724-781 (2011).</li><li>Liu, J., Thallapally, P. K., McGrail, B. P., Brown, D. R., Liu, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Progress+in+adsorption-based+CO2+capture+by+metal-organic+frameworks.">Progress in adsorption-based CO2 capture by metal-organic frameworks.</a> Chem. Soc. Rev. 41, 2308-2322 (2012).</li><li>Lee, J., 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=Metal-organic+framework+materials+as+catalysts.">Metal-organic framework materials as catalysts.</a> Chem. Soc. Rev. 38, 1450-1459 (2009).</li><li>Yoon, M., Srirambalaji, R., Kim, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Homochiral+Metal&#8211;Organic+Frameworks+for+Asymmetric+Heterogeneous+Catalysis.">Homochiral Metal&#8211;Organic Frameworks for Asymmetric Heterogeneous Catalysis.</a> Chem. Rev. 112, 1196-1231 (2011).</li><li>Kreno, L. E., 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=Metal&#8211;Organic+Framework+Materials+as+Chemical+Sensors.">Metal&#8211;Organic Framework Materials as Chemical Sensors.</a> Chem. Rev. 112, 1105-1125 (2011).</li><li>Chen, B., Xiang, S., Qian, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal&#8722;Organic+Frameworks+with+Functional+Pores+for+Recognition+of+Small+Molecules.">Metal&#8722;Organic Frameworks with Functional Pores for Recognition of Small Molecules.</a> Acc. Chem. Res. 43, 1115-1124 (2010).</li><li>Wang, J. L., Wang, C., Lin, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal&#8211;Organic+Frameworks+for+Light+Harvesting+and+Photocatalysis.">Metal&#8211;Organic Frameworks for Light Harvesting and Photocatalysis.</a> ACS Catalysis. 2, 2630-2640 (2012).</li><li>Lewis, D. W., 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=Zeolitic+Imidazole+Frameworks:+Structural+and+Energetics+Trends+Compared+with+their+Zeolite+Analogues.">Zeolitic Imidazole Frameworks: Structural and Energetics Trends Compared with their Zeolite Analogues.</a> CrystEngComm. 11, 2272-2276 (2009).</li><li>Mondloch, J. E., Karagiaridi, O., Farha, O. K., Hupp, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+metal-organic+framework+materials.">Activation of metal-organic framework materials.</a> CrystEngComm. 15, 9258-9264 (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=Synthesis+and+characterization+of+isostructural+cadmium+zeolitic+imidazolate+frameworks+via+solvent-assisted+linker+exchange.">Synthesis and characterization of isostructural cadmium zeolitic imidazolate frameworks via solvent-assisted linker exchange.</a> Chemical Science. 3, 3256-3260 (2012).</li><li>Burnett, B. J., Barron, P. M., Hu, C., Choe, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stepwise+Synthesis+of+Metal&#8211;Organic+Frameworks:+Replacement+of+Structural+Organic+Linkers.">Stepwise Synthesis of Metal&#8211;Organic Frameworks: Replacement of Structural Organic Linkers.</a> J. Am. Chem. Soc. 133, 9984-9987 (2011).</li><li>Kim, M., Cahill, J. F., Su, Y., Prather, K. A., Cohen, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Postsynthetic+ligand+exchange+as+a+route+to+functionalization+of+&amp;#34;inert&amp;#34;+metal-organic+frameworks.">Postsynthetic ligand exchange as a route to functionalization of &amp;#34;inert&amp;#34; metal-organic frameworks.</a> Chemical Science. 3, 126-130 (2012).</li><li>Bury, W., 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=Control+over+Catenation+in+Pillared+Paddlewheel+Metal&#8211;Organic+Framework+Materials+via+Solvent-Assisted+Linker+Exchange.">Control over Catenation in Pillared Paddlewheel Metal&#8211;Organic Framework Materials via Solvent-Assisted Linker Exchange.</a> Chem. 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. Soc. , (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+ZIF-8:+A+Catalytically+Active+Zeolitic+Imidazolate+Framework+of+Sodalite+Topology+with+Unsubstituted+Linkers.">Opening ZIF-8: A Catalytically Active Zeolitic Imidazolate Framework of Sodalite Topology with Unsubstituted Linkers.</a> J. Am. Chem. Soc. 134, 18790-18796 (2012).</li><li>Takaishi, S., DeMarco, E. J., Pellin, M. J., Farha, O. K., Hupp, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvent-assisted+linker+exchange+(SALE)+and+post-assembly+metallation+in+porphyrinic+metal-organic+framework+materials.">Solvent-assisted linker exchange (SALE) and post-assembly metallation in porphyrinic metal-organic framework materials.</a> Chemical Science. 4, 1509-1513 (2013).</li><li>Vermeulen, N. A., 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=Aromatizing+Olefin+Metathesis+by+Ligand+Isolation+inside+a+Metal&#8211;+Organic+Framework.">Aromatizing Olefin Metathesis by Ligand Isolation inside a Metal&#8211; Organic Framework.</a> J. Am. Chem. Soc. 135, 14916-14919 (2013).</li><li>Nelson, A. P., Farha, O. K., Mulfort, K. L., Hupp, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Supercritical+Processing+as+a+Route+to+High+Internal+Surface+Areas+and+Permanent+Microporosity+in+Metal&#8722;Organic+Framework+Materials.">Supercritical Processing as a Route to High Internal Surface Areas and Permanent Microporosity in Metal&#8722;Organic Framework Materials.</a> J. Am. Chem. Soc. 131, 458-460 (2008).</li><li>Farha, O. K., 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=De+novo+synthesis+of+a+metal&#8211;organic+framework+material+featuring+ultrahigh+surface+area+and+gas+storage+capacities.">De novo synthesis of a metal&#8211;organic framework material featuring ultrahigh surface area and gas storage capacities.</a> Nat Chem. 2, 944-948 (2010).</li><li>Furukawa, H., 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=Ultrahigh+Porosity+in+Metal-Organic+Frameworks.">Ultrahigh Porosity in Metal-Organic Frameworks.</a> Science. 329, 424-428 (2010).</li><li>Farha, O. K., Malliakas, C. D., Kanatzidis, M. G., Hupp, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+over+Catenation+in+Metal&#8722;Organic+Frameworks+via+Rational+Design+of+the+Organic+Building.">Control over Catenation in Metal&#8722;Organic Frameworks via Rational Design of the Organic Building.</a> J. Am. Chem. Soc. 132, 950-952 (2009).</li><li>Shultz, A. M., Sarjeant, A. A., Farha, O. K., Hupp, J. T., Nguyen, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Post-Synthesis+Modification+of+a+Metal&#8211;Organic+Framework+To+Form+Metallosalen-Containing+MOF+Materials.">Post-Synthesis Modification of a Metal&#8211;Organic Framework To Form Metallosalen-Containing MOF Materials.</a> J. Am. Chem. Soc. 133, 13252-13255 (2011).</li><li>Li, H., Eddaoudi, M., O&#39;Keeffe, M., Yaghi, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+synthesis+of+an+exceptionally+stable+and+highly+porous+metal-organic+framework.">Design and synthesis of an exceptionally stable and highly porous metal-organic framework.</a> Nature. 402, 276-279 (1999).</li><li>Ferey, G., 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=Chromium+Terephthalate-Based+Solid+with+Unusually+Large+Pore+Volumes+and+Surface+Area.">Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area.</a> Science. 309, 2040-2042 (2005).</li><li>Cavka, J. H., 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=A+New+Zirconium+Inorganic+Building+Brick+Forming+Metal+Organic+Frameworks+with+Exceptional+Stability.">A New Zirconium Inorganic Building Brick Forming Metal Organic Frameworks with Exceptional Stability.</a> J. Am. Chem. Soc. 130, 13850-13851 (2008).</li><li>Chen, Z., Xiang, S., Zhao, D., Chen, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversible+Two-Dimensional&#8722;Three+Dimensional+Framework+Transformation+within+a+Prototype+Metal&#8722;Organic+Framework.">Reversible Two-Dimensional&#8722;Three Dimensional Framework Transformation within a Prototype Metal&#8722;Organic Framework.</a> Crystal Growt., &amp; Design. 9, 5293-5296 (2009).</li><li>Walton, K. S., Snurr, R. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applicability+of+the+BET+Method+for+Determining+Surface+Areas+of+Microporous+Metal&#8722;Organic+Frameworks.">Applicability of the BET Method for Determining Surface Areas of Microporous Metal&#8722;Organic Frameworks.</a> J. Am. Chem. Soc. 129, 8552-8556 (2007).</li></ol>

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 ...

synthesis-characterization-functionalized-metal-organic

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 surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

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 Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

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

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

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. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

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)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

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

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

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. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Here, we demonstrate a protocol for the two-step synthesis of single-crystalline core-shells using a non-isostructural metal-organic framework (MOF) pair, HKUST-1 and MOF-5, which have well-matched crystal lattices.

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 tunability. However, the progression of MOF-based photochemistry has been hindered by the difficulty in spectrally characterizing these materials. Given that MOFs are typically larger than 100 nm in size, they are prone to excessive light scatter, thereby rendering data from valuable analytical tools like transient absorption and emission spectroscopy nearly uninterpretable. To gain meaningful insights of MOF-based photo-chemical and physical processes, special consideration must be taken toward properly preparing MOFs for spectroscopic measurements, as well as the experimental setups that garner higher quality data. With these considerations in mind, the present guide provides a general approach and set of guidelines for the spectroscopic investigation of MOFs. The guide addresses the following key topics: (1) sample preparation methods, (2) spectroscopic techniques/measurements with MOFs, (3) experimental setups, (3) control experiments, and (4) post-run stability characterization. With appropriate sample preparation and experimental approaches, pioneering advancements toward the fundamental understanding of light-MOF interactions are significantly more attainable.

Here, we use a polymer stabilizer to prepare metal-organic framework (MOF) suspensions that exhibit markedly decreased scatter in their ground-state and transient absorption spectra. With these MOF suspensions, the protocol provides various guidelines to characterize the MOFs spectroscopically to yield interpretable data.

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

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, energy, and catalysis. Recently, low-valent MOFs (LVMOFs) have been explored for their potential use as heterogeneous catalysts, and multitopic phosphine linkers have been shown to be a useful building block for the formation of LVMOFs. However, the synthesis of LVMOFs using phosphine linkers requires conditions that are distinct from those in the majority of the MOF synthetic literature, including the exclusion of air and water and the use of unconventional modulators and solvents, making it somewhat more challenging to access these materials. This work serves as a general tutorial for the synthesis of LVMOFs with phosphine linkers, including information on the following: 1) the judicious choice of the metal precursor, modulator, and solvent; 2) the experimental procedures, air-free techniques, and required equipment; 3) the proper storage and handling of the resultant LVMOFs; and 4) useful characterization methods for these materials. The intention of this report is to lower the barrier to this new subfield of MOF research and facilitate advancements toward novel catalytic materials.

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

Here, we describe a protocol for the synthesis of low-valent metal-organic frameworks (LVMOFs) from low-valent metals and multitopic phosphine linkers under air-free conditions. The resulting materials have potential applications as heterogeneous catalyst mimics of low-valent metal-based homogeneous catalysts.

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

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs show outstanding performance in terms of gravimetric or areal capacitance and cyclic stability, unfortunately their electrochemical mechanisms are not well understood in most cases. Traditional spectroscopic techniques, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), have only provided vague and qualitative information about valence changes of certain elements, and the mechanisms proposed based on such information are often highly disputable. In this article, we report a series of standardized methods, including the fabrication of solid-state electrochemical cells, electrochemistry measurements, the disassembly of cells, the collection of MOF electrochemical intermediates, and physical measurements of the intermediates under the protection of inert gases. By using these methods for quantitatively clarifying the electronic and spin state evolution within a single electrochemical step of redox-active MOFs, one can provide clear insight into the nature of electrochemical energy storage mechanisms not only for MOFs, but also for all other materials with strongly correlated electronic structures.

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

Ex situ magnetic surveys can directly provide bulk and local information on a magnetic electrode to reveal its charge storage mechanism step by step. Herein, electron spin resonance (ESR) and magnetic susceptibility are demonstrated to monitor the evaluation of paramagnetic species and their concentration in a redox-active metal-organic framework (MOF).

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

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. Given their coordinative nature, the organic ligands and strut framework can be readily removed from the MOF and/or exchanged with other coordinative molecules. By introducing target ligands to MOF-containing solutions, functionalized MOFs can be obtained with new chemical tags via a process called post-synthetic ligand exchange (PSE). PSE is a straightforward and practical approach that enables the preparation of a wide range of MOFs with new chemical tags via a solid-solution equilibrium process. Furthermore, PSE can be performed at room temperature, allowing the incorporation of thermally unstable ligands into MOFs. In this work, we demonstrate the practicality of PSE by using heterocyclic triazole- and tetrazole-containing ligands to functionalize a Zr-based MOF (UiO-66; UiO = University of Oslo). After digestion, the functionalized MOFs are characterized via various techniques, including powder X-ray diffraction and nuclear magnetic resonance spectroscopy.

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

Post-synthetic ligand exchange (PSE) is a versatile and powerful tool for installing functional groups into metal-organic frameworks (MOFs). Exposing MOFs to solutions containing triazole- and tetrazole-functionalized ligands can incorporate these heterocyclic moieties into Zr-MOFs through PSE processes.

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