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 (CAUTION! Corrosive to eyes, skin and mucous membrane. Handle with gloves.).</li>
	<li>Tightly cap the vial and thoroughly mix the ingredients using an ultrasonication bath for ~15 min. Observe the contents of the vial as they form a suspension.</li>
	<li>Place the vial in an oven at 80 &#186;C for two days. On day 1, check the vial to ensure that its contents have completely dissolved, forming a yellow clear solution. On day 2, observe yellow tear-shaped crystals on the walls and the bottom of the vial. Following the formation of the crystals, remove the vial from the oven.</li>
	<li>Allow the vial to cool to RT. Then use a spatula to gently push the crystals off the vial walls, so that they all collect on the floor of the vial. Let the vial stand for ~5 min to ensure that all the crystals have settled on the floor.</li>
	<li>Using a 9&#8217;&#8217; Pasteur pipet, gently remove the reaction solution from the vial, while avoiding sucking up the crystals into the pipet. Leave just enough solution so that the crystals are completely covered, to prevent the framework from drying out.</li>
	<li>Add ~5 ml fresh DMF to the vial with the crystals. Soak the MOF crystals in fresh DMF for at least one day in order to remove the acidic reaction solution and any unreacted ingredients trapped in the MOF pores. For best results, periodically replace the DMF with fresh batches (~3 times over the course of the first hour, then every 6-12 hr).</li>
	<li>Store the Br-YOMOF crystals in DMF at RT until further use.</li>
</ol>
2. Characterization by Powder X-ray Diffraction (PXRD)
<ol>
	<li>Prepare a 0.7 mm diameter borosilicate glass capillary for the experiment by carefully cutting off the closed end so that the top 3 cm of the capillary (with the funnel top) remain.</li>
	<li>Heat regular beeswax until it is melted and dip the narrow (cut) end of the capillary into the melted wax. Remove the capillary and let the wax solidify as a plug in the bottom of the capillary.</li>
	<li>Support the capillary in a small amount of modeling clay.</li>
	<li>Using a Pasteur pipet, draw up several milliliters of crystals in solution. Carefully transfer the crystals and solution to the capillary though the funnel opening. Use a paper towel or tissue to wick away excess solvent. Avoid spilling solvent or crystals on the outside of the capillary.</li>
	<li>Allow the crystals to settle into a small plug (approximately 2-5 mm in length). Use a very small piece of modeling clay to seal the top (funnel) end of the capillary.</li>
	<li>Remove any mounting devices from the goniometer head (brass pins, magnetic mounts, etc.) and place your capillary supported by modeling clay on top of the goniometer head.</li>
	<li>Center the capillary in the X-ray beam to ensure that the plug of crystals does not precess as it rotates. 
	NOTE: The volume of crystalline material will exceed the beam size of most standard laboratory X-ray sources.</li>
	<li>Using your diffractometer&#8217;s software, prepare a series of 180&#176; &#966; scans, in overlapping increments of 2&#952;. For example, using a kappa-geometry diffractometer equipped with an Apex2 detector set at 150 mm (dx), we collect a series of 10-sec, 180&#176; &#966; scans with the parameters as per Table 1.</li>
	<li>Once the frames have been collected, use your diffractometer&#8217;s software to combine all images and integrate over the resultant diffraction pattern.</li>
</ol>
3. Performing Solvent-assisted Linker Exchange (SALE) on Br-YOMOF Crystals
<ol>
	<li>Weigh out 21 mg of dped (0.095 mmol) and dissolve it in 5 ml DMF in a 2-dram vial with ultrasonication.</li>
	<li>Using a 6&#8217;&#8217; Pasteur pipet, collect the Br-YOMOF crystals and filter them on a Buchner funnel. Then weigh out ~30 mg of the crystals; return the rest of the crystals to the vial with Br-YOMOF.</li>
	<li>Disperse the crystals in the previously prepared dped solution. Place the resulting SALE mixture in an oven at 100 &#186;C for 24 hr.</li>
	<li>On the next day, check the progress of the SALE reaction with 1H NMR. With a spatula or a 6&#8217;&#8217; Pasteur pipet, remove approximately 2-5 mg of the MOF crystals from the reaction DMF solution. Rinse these crystals by submerging them in a small amount of clean solvent (low boiling solvent such as dichloromethane, or same solvent as the reaction medium &#8212; in this case DMF) in a 1.5-dram vial.</li>
	<li>Add ~1 ml deuterated dimethyl sulfoxide (d6-DMSO) in a separate 1.5-dram vial. Filter out the crystals from the cleaning solution and disperse them in d6-DMSO. Dissolve the crystals by adding 3 drops of deuterated sulfuric acid (D2SO4) to the mixture. Thoroughly sonicate the capped vial to obtain a homogeneous solution.</li>
	<li>Transfer the resulting NMR sample to an NMR tube with a Pasteur pipet and collect the NMR spectrum. Perform 64 scans, since the solution is relatively dilute due to the low solubility of the MOF crystals.</li>
	<li>Interpret the spectrum by verifying that all the dpni has been replaced by dped, and that the dped:Br-tcpb ratio is 1:1. 
	NOTE: If dpni is still present in the crystals, return the vial with the reaction mixture to the oven and keep monitoring the reaction with 1H NMR until the desired product is obtained.</li>
	<li>If all dpni has been replaced by dped, stop the reaction by decanting the reaction solution with a 9&#8217;&#8217; Pasteur pipet and replacing it with fresh DMF. Perform additional characterization of the SALEM-5 crystals by collecting their PXRD pattern; then store the crystals in DMF until further use.</li>
</ol>
4. Activating SALEM-5 Crystals with Supercritical CO2 Drying
<ol>
	<li>Prior to activation, exchange all the DMF from the MOF cages with ethanol, which is miscible with liquid CO2 and compatible with the supercritical dryer. Perform solvent replacement by decanting the DMF from the MOF vial with a 9&#8217;&#8217; Pasteur pipet and replacing it with a small amount of ethanol (enough to completely submerge the crystals).</li>
	<li>Continue the solvent exchange for 3 days, replacing the ethanol with a fresh batch every day. Ensure that all the DMF has been removed from the crystal pores by collecting a 1H NMR spectrum of the crystals.</li>
	<li>Check that a tank with sufficient liquid CO2 is connected to the supercritical dryer.</li>
	<li>Transfer the MOF crystals to an activation dish using a 6&#8217;&#8217; Pasteur pipet. Then remove as much of the ethanol as possible with a 9&#8217;&#8217; Pasteur pipet while avoiding sucking the crystals up into the pipet.</li>
	<li>Remove the lid of the activation chamber by unscrewing the three bolts and inspect the chamber for residual MOF debris (if those are present, wipe the chamber clean with a Kimwipe). Using a pair of forceps, insert the activation dish with the MOF into the chamber and screw the lid back into its place.</li>
	<li>Turn the dryer on and open the CO2 tank. Adjust the temperature knob to achieve a temperature between 0 and 10 &#186;C. Maintain that temperature range throughout the activation process to keep CO2 in its liquid state.</li>
	<li>Once the temperature is in the correct range, turn up the &#8220;fill&#8221; knob slowly. Observe liquid CO2 pouring into the activation dish through the glass window on the chamber lid. At the same time the pressure reading on the gauge should increase until it reaches 800 psi.</li>
	<li>Perform the first &#8220;purge&#8221;, that is the first replacement of the activation solvent with a fresh batch. First turn the &#8220;fill&#8221; knob up to the mark that reads 15. Then slowly turn up the &#8220;purge&#8221; knob until a jet of solvent shoots out from the tube on the side of the instrument. Let the purge go on for ~5 min; then close the &#8220;purge&#8221; knob and turn the &#8220;fill&#8221; knob down to the mark that reads 5.</li>
	<li>Continue the supercritical drying for 8 hr, performing a &#8220;purge&#8221; every 2 hr.</li>
	<li>After 8 hr, turn all the knobs off and flip the &#8220;heat&#8221; switch on. Wait until the temperature and pressure exceed the supercritical point (31 &#186;C and 1,070 psi).</li>
	<li>Connect a flowmeter to the tube on the side of the instrument and open the &#8220;bleed&#8221; knob. Adjust the flow to 1 cm3/min; then remove the flowmeter and let the CO2 slowly bleed from the sample (which typically takes place O/N).</li>
	<li>The next day, check that the pressure has dropped to 0 psi; if it has not, turn up the &#8220;bleed&#8221; knob until you achieve the desired pressure drop. Close the &#8220;bleed&#8221; knob and turn off the &#8220;heat&#8221; and power switches on the instrument.</li>
	<li>Remove the sample from the activation chamber. Cap the activation dish tightly and wrap it in Parafilm. Store the activated SALEM-5 in a glove box until further use. Make sure that no ethanol is present in the sample by collecting a 1H NMR spectrum.</li>
</ol>
5. Collecting a N2 Isotherm of the MOF to Obtain Its BET Surface Area
<ol>
	<li>Obtain a sorption tube equipped with a filler rod and a seal frit and accurately weigh it. Weigh it at least two times and make sure the two balance readings agree with each other within &#177;0.01 mg.</li>
	<li>Transfer the pre-weighed tube to the glove box and load the activated SALEM-5 sample inside the tube. We recommend using a clean, dry funnel, as activated MOF samples stored in the glove box are often electrostatically charged and difficult to handle. Remove the seal frit and the filler rod from the tube and fit it with a funnel; then rapidly invert the activation dish over the funnel, making sure the sample slides down the tube.</li>
	<li>Reinsert the filler rod and the seal frit into the tube loaded with SALEM-5. Slide the filler rod slowly and carefully into the tube to avoid spilling the sample and/or breaking the tube. Remove the tube from the glove box.</li>
	<li>Weigh the loaded tube accurately, using the same technique (and the same balance) that you used to load the empty tube.</li>
	<li>Place an isothermal jacket on the tube, load the tube on the sorption instrument and set up the sorption file by entering the masses of the empty tube and the tube with the sample. Adjust the file to evacuate the sample on the instrument for 1 hr prior to the collection of the isotherm.</li>
	<li>Ensure that the Dewar used to store the liquid nitrogen is free from ice and/or water by filling it with water to allow the ice to thaw and then wiping it dry. Fill the Dewar with liquid nitrogen to the appropriate mark and start the measurement. The measurement lasts anywhere from 4 to 12 hr, depending on the amount and the porosity of the material.</li>
</ol>

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The authors have nothing to disclose.

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 ...

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47.9K vistas.  Northwestern University.  Síntesis, activación, y caracterización de materiales para estructuras metal-orgánicos diseñados intencionalmente es un reto, especialmente cuando los bloques de construcción son polimorfos incompatibles o no deseados son favorecidas termodinámicamente sobre las formas deseadas. Se describe cómo las aplicaciones de intercambio enlazador disolvente asistida, polvo de difracción de rayos X en los capilares y la activación a través de CO2 supe...

Video: Synthesis and Characterization of Functionalized Metal-organic Frameworks

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. ...