Hydrothermal Synthesis and Characterization of a MetalminusOrganicFramework by Thermogravimetric Analysis Powder X‑rayDiffraction and Infrared Spectroscopy An Integrative InorganicChemistry ExperimentJohanna L Crane Kelly E Andersondagger and Samantha G Conway

Department of Chemistry University of Puget Sound Tacoma Washington 98416 United States

S Supporting Information

ABSTRACT This advanced undergraduate laboratory experimentinvolves the synthesis and characterization of a metalminusorganicframework with microporous channels that are held intact viahydrogen bonding of the coordinated water molecules Thehydrothermal synthesis of Co3(BTC)2middot12H2O (BTC = 135-benzenetricarboxylic acid) is carried out using one of four different reactors(stainless steel microwave polypropylene bottle or sealed glassampules) and the products are evaluated and compared usingthermogravimetric analysis powder X-ray diffraction and IRspectroscopy Powder X-ray diffraction is also used to monitor thechanges in structure of the framework during the partial or complete removal of the associated water molecules as well as afterreabsorption of water

KEYWORDS Upper-Division Undergraduate Inorganic Chemistry Laboratory Instruction Gravimetric Analysis Hydrogen BondingIR Spectroscopy Materials Science Thermal Analysis

Metalminusorganic frameworks (MOFs)1 are a literal andfigurative extension of coordination chemistry2 These

crystalline materials employ organic substituents (ligands) tolink multiple metal centers together By adjusting the length ofthe organic ligand the size of the formed cavity or pore can becontrolled Not only can the pore size be controlled withchemical synthesis but the shape of the pore can also bespecifically designed by employing organic ligands withdifferent functionalities or different metal centers Metals havepreferred coordination geometries (octahedral tetrahedralsquare planar etc) therefore they direct the assembly of theframework Secondary interactions such as hydrogen bondingor πminusπ stacking may also contribute to the architecture of thestructure Metalminusorganic frameworks can be custom-tailoredfor specific purposes such as small molecule storage andtransport size- or shape-selective separation and catalysis andhave potential in other areas such as drug delivery anddiagnostics Special thematic issues3 in Chemical ReviewsChemical Society Reviews and the New Journal of Chemistryprovide an excellent background on the advances in MOFchemistryThe experiment described here includes the synthesis of a

MOF and the characterization of the structure usingthermogravimetic analysis (TGA) powder X-ray diffraction(XRD) and IR spectroscopy Although TGA and XRD areimportant techniques in chemistry and materials science theyare not commonly used by chemistry undergraduatesPreviously published laboratory experiments that involve

MOFs have focused on the measurement of the internalsurface area4 and investigating the hostminusguest relationship5

The unique aspect of the system reported herein is that thewater molecules associated with the framework are not simplyguest molecules but are important in maintaining structuralintegrity of the framework Students use TGA IR spectroscopyand XRD in an integrative fashion to learn how the removal ofsome or all of the water (and subsequent rehydration) affectsthe overall stability of the frameworkAnother important aspect of this experiment is that it

highlights the differences in the synthetic conditions required toproduce a MOF versus a discrete coordination complexStudents have most likely encountered traditional synthetictechniques to prepare discrete complexes however to producestable metalminusligand bonds throughout the framework harshersynthetic conditions (such as hydrothermal synthesis) aregenerally required to obtain the most robust thermodynamicproduct2 Hydrothermal synthesis involves the extendedheating of the reactants in water at elevated temperatures andpressuresOver the past 12 years this experiment has developed into a

multiperiod synthesis characterization and analysis experimentthat encourages upper-level undergraduates in InorganicChemistry or an Advanced Laboratory to review the literaturesearch the crystallographic database and critically interpret thecombined output from the analytical techniques to describe the

Laboratory Experiment

pubsacsorgjchemeduc

copy XXXX American Chemical Society andDivision of Chemical Education Inc A dxdoiorg101021ed5000839 | J Chem Educ XXXX XXX XXXminusXXX

effects of the dehydrationrehydration process This experi-ment generates a tremendous amount of data so during thecourse of the data collection the students discuss whatinformation the data provide about the product Students arethen assigned focused discussion topics in which they use theappropriate data literature and so forth to organize and write amore scientific-style Results and Discussion section (asopposed to a standard lab report)6 This nontraditional labexperiment transitions students from a ldquocookbookrdquo experimentto a more research-style laboratory scenario

EXPERIMENTAL OVERVIEW

In 1996 porous solids of the formula M3(BTC)2middot12H2O (M =Co Ni Zn) were produced by reacting M(II) acetate hydratewith 135-benzenetricarboxylic acid (H3BTC) in a hydro-thermal fashion7 Hydrothermal synthesis is a commonpreparation technique of MOFs that normally entails heatingan aqueous mixture of reactants in a stainless steel vesselautoclave to temperatures well above the boiling point of water(120minus350 degC) Stainless steel vessels (Parr reactors) are thesafe and accepted containers for hydrothermal synthesishowever they are expensive Microwave reactors are becomingmore common place in the undergraduate laboratory8 so asynthetic method was designed using a microwave reactorAdditionally some commonly available equipmentnarrowmouth polypropylene bottles and vacuum-sealed glass tubescan safely and effectively serve as reactors for the hydrothermalsynthesis of Co3(BTC)2middot12H2O (Although we have studiedthe nickel and zinc analogues we have most extensively workedwith the cobalt complex due to the distinctive color changeassociated with the dehydration of the material)The resulting open framework structure of Co3(BTC)2middot

12H2O is constructed from both covalent interactions andhydrogen bonding interactions resulting in channels that are 4times 5 Aring and it is these hydrogen bonding interactions that helpassemble the coordination polymer into a porous framework7

Figure 1 highlights a portion of the Co3(BTC)2middot12H2O unit ofthe coordination polymer (A coordination polymer is definedas ldquoa coordination compound with repeating coordinationentities in 1 2 or 3 dimensionsrdquo MOFs are considered asubclass of multidimensional coordination polymers1)With this experiment students experience a different

synthetic technique and observe how the synthetic conditionsaffect the properties of the product Students integrate datafrom multiple instrumental techniques and work in a research-like setting to determine what each piece of data provides to theoverall picture of structure and bonding within this materialand they learn the limits of what conclusions can be drawnfrom each analytical technique

EXPERIMENT

This advanced laboratory experiment has been typicallyperformed in three separate 4-h lab periods but may beperformed in two lab periods if individual student groups carryout the analysis of one technique and collaborate with othergroups on their findings Students work in pairs to prepareCo3(BTC)2middot12H2O by heating an aqueous mixture of cobalt-(II) acetate and H3BTC in one of the four reactors Detailedsafety precautions and the experimental methods utilized foreach hydrothermal reactor are provided in the SupportingInformation Formation of the product is verified by IRspectroscopy and powder XRD and the solubility of the

product is tested and compared to the starting materialsThermogravimetric analysis is performed to determine theamount of water removed at a given temperature and XRD isused to monitor the changes to the structure of the frameworkduring the partial or complete removal of the associated watermolecules as well as after reabsorption of water

HAZARDSCobalt(II) acetate tetrahydrate is a suspected carcinogenCobalt(II) acetate tetrahydrate and 135-benzenetricarboxylicacid are known skin and respiratory irritants Proper eyeprotection and nitrile gloves should be worn and work shouldbe done in a fume hood to minimize exposure The hazards ofthe product Co3(BTC)2middot12H2O have not been assessedhowever it is handled in a similar fashion as the reactantsThe hydrothermal process is carried out by heating an

aqueous mixture in a closed container The elevated pressuresinside the container may cause catastrophic failure of thecontainer Goggles and insulated gloves should be worn whenhandling the reaction container

RESULTS AND DISCUSSION

Synthesis

Average yields of Co3(BTC)2middot12H2O were 63 (glass ampule)78 (polypropylene bottle) 81 (microwave) and 82(stainless steel vessel) The low yield associated with theglass ampule was most likely a result of the reactants not mixingvery well in the narrow tube during the synthesis yet attemptsto mix the reactants before sealing the tube did not statisticallyimprove the yield In the stainless steel reactor the crystallineproduct was obtained after heating the sample at 140 degC forless than 2 days Hydrothermal reactions performed in thepolypropylene bottles were carried out at a lower temperature

Figure 1 Co3(BTC)2middot12H2O repeating unit of the coordinationpolymer strand Different water molecules (differentiated by color) canform different hydrogen bonding interactions (in red) watermolecules that form hydrogen bonds to adjacent BTC units withinthe single coordination polymer strand that is shown (in blue) watermolecules that form hydrogen bonds to water molecules on anadjacent coordination polymer strand and (in purple) the watermolecule that can hydrogen bond in either mode Hydrogen atoms onthe BTC unit have been omitted for clarity Data from ref 7

Journal of Chemical Education Laboratory Experiment

dxdoiorg101021ed5000839 | J Chem Educ XXXX XXX XXXminusXXXB

(105 degC) but this did not have a significant effect on the yieldor the phase purity of the material The microwave reactorproved to be the quickest most efficient method (30 min at 80degC) to produce Co3(BTC)2middot12H2O The most notabledifference between the Co3(BTC)2middot12H2O samples was thatdark pink crystals formed in the stainless steel vessel whereaspink powdery products were isolated by the other methodsonly the former method utilized a slow temperature cool downwhich tended to favor crystalline growthCharacterization

The Supporting Information provides IR TGA and XRD datacollected by students that demonstrate that Co3(BTC)2middot12H2Ois produced independent of the hydrothermal reactoremployed A unique characteristic of Co3(BTC)2middot12H2O isthat the sample undergoes a distinct change in color duringdehydration The fully hydrated sample is dark pink andtransitions through purple when partially dehydrated to bluewhen completely dehydrated This color change is similar tothat observed in humidity detection strips that are impregnatedwith hydrated cobalt(II) chloride the hydrated octahedralcomplex is pink whereas the (nearly) anhydrous cobalt(II)chloride tetrahedral complex is blue9

A thermogram of Co3(BTC)2middot12H2O collected by students(Figure 2) outlines the weight loss due to dehydration of the

coordinated water molecules At 100 degC the weight loss of25 corresponds to the loss of 11 water molecules performula unit and by 200 degC the weight loss corresponds to theloss of almost 115 H2O molecules The sample is fullydehydrated (minus12 H2O) above 290 degC which is lower thanreported7a this is likely due to different heating rates Becausethe only thermal event for Co3(BTC)2middot12H2O is loss of waterthe determination of the amount of water removed at aparticular temperature could be performed using traditionalgravimetric analysis methods with careful repetitive analyticalweighing before and after heating a sampleThe IR spectrum of Co3(BTC)2middot12H2O (Supporting

Information) matches that reported7a and can be comparedto that of the starting material (135-benzenetricarboxylic acid)The lack of the 1730minus1690 cmminus1 absorption band inCo3(BTC)2middot12H2O indicates that the BTC unit was deproto-nated to form carboxylate The broad absorption bandsbetween 3467minus3125 cmminus1 indicate the presence of water in

the complex and these absorption bands diminish with thepartial and complete dehydration of the complexPowder X-ray diffraction is utilized to determine the phase

purity of Co3(BTC)2middot12H2O as well to monitor thecrystallinity of the structure as the water molecules are partiallyor completely removed and reabsorbed Figure 3 shows

representative student-acquired powder XRD patterns ofCo3(BTC)2middot12H2O that highlight the changes in thecrystallinity during the partial dehydration and rehydrationprocess The lowest pattern in Figure 3 is obtained from theprepared Co3(BTC)2middot12H2O and indicates that the materialhas long-range atomic order with three low angle majorreflections at 173 184 and 267 2θ (deg) When the materialis partially dehydrated the broadening in the diffraction patternindicates that deformation in the crystalline lattice is occurring(Figure 3 middle patterns) Due to the lower intensity of thesediffraction patterns in comparison to the original product theyappear flat in the overlay however for a better view of thebroadening see Figure S8 in the Supporting Information Afterthe sample is rehydrated by soaking in water for 5minus10 min theoriginal diffraction pattern is nearly restored with only minorchanges in the position or intensity of the reflections (Figure 3top) A deformation in the crystalline latticeversus acomplete loss of crystallinityduring the partial dehydrationis supported because the rehydration process occurs instantlywithout the sample dissolving and recrystallizing Therehydration of partially dehydrated samples containing varyingamounts of water (Co2(BTC)3middot(1minus11)H2O) has beeninvestigated and in all cases the crystallinity of the frameworkis reestablished as determined by XRD However when acompletely dehydrated sample is rehydrated the originalstructure is not restored indicating a collapse in the structureand the loss of crystallinity in the framework (see Figure S10 inSupporting Information) Therefore the reversibility of thedehydrationminusrehydration process is contingent upon having atleast one water molecule (per formula unit) present as part ofthe framework to provide the hydrogen bonding interactionsnecessary to maintain the integrity of the framework Thisallows water molecules to reenter the voids that form duringdehydration To view the bonding students may refer to Figure1 (or the handout in Supporting Information) In order to view

Figure 2 Thermogram for Co3(BTC)2middot12H2O under a nitrogen flowwith a heating rate of 5 degCmin to 300 degC

Figure 3 Powder XRD patterns of Co3(BTC)2middot12H2O duringdifferent stages of dehydration and reabsorption of water The bottompattern (black) is for the ldquoas preparedrdquo sample synthesized via thestainless steel reactor the middle patterns are for partially dehydratedsamples Co3(BTC)2middot73H2O (purple) and Co3(BTC)2middot375H2O(blue) the top pattern (red) is for the fully rehydrated sample

Journal of Chemical Education Laboratory Experiment

dxdoiorg101021ed5000839 | J Chem Educ XXXX XXX XXXminusXXXC

the channels in the crystal structure students may refer to theoriginal article7 or they may obtain the crystallographicinformation file (cif) through the Cambridge StructuralDatabase and view on software made available from thesite10 This illustrates to students that the role of water in theCo3(BTC)2 framework is more than that of a guest it is criticalin stabilizing the framework (via hydrogen bonding)Guest dependent pore stability has been observed to a lesser

extent during the dehydration of different BTC-containingMOFs [M(HBTC)(H2O)2]middot05H2O (M = Sr or Ba)11

Although the resulting channels in [M(HBTC)(H2O)2]middot05H2O are almost double in size of Co3(BTC)2middot12H2O theobserved deformation of the former structure duringdehydration is minimal due to the fact that fewer watermolecules per cation are being liberated than in theCo3(BTC)2middot12H2O structure

SUMMARYCo3(BTC)2middot12H2O can be safely and effectively prepared byhydrothermal synthesis using a variety of reactors Thermog-ravimetric analysis provides the temperature range throughwhich dehydration occurs Structural changes to the frameworkthat occur during the partial dehydration and reabsorption ofthe included water molecules are monitored with powder X-raydiffraction With this experiment students learn new syntheticand instrumental techniques and integrate their findings inorder to explain factors that affect the reversibility of thedehydrationminusrehydration process of this MOF The studentsrsquolevel of understanding and ability to consider data frommultiple sources are mainly assessed through discussions withthem in the laboratory and by reading their journal-style Resultsand Discussion reportStudents have investigated the synthesis or the dehydration

process beyond the basic experiment and such further studieshave included optimizing the reaction conditions withalternative hydrothermal reactors12 to produce Co3(BTC)2middot12H2O investigating the inclusion of ammonia7a into a partiallydehydrated sample of Co3(BTC)2middotxH2O and the (hydro-thermal solvothermal or traditional) synthesis and character-ization of other metalminusBTC materials1113 These studies arebriefly outlined in the Supporting Information Although thisexperiment has been presented as an advanced experiment itcould be easily tailored to introduce inorganic materials andsimple gravimetric analysis at the introductory level

ASSOCIATED CONTENT

S Supporting Information

This section includes experimental details for students alongwith safety precautions instructor notes with purchasinginformation ideas for further studies and additional datacollected by students This material is available via the Internetat httppubsacsorg

AUTHOR INFORMATION

Corresponding Author

E-mail jcranepugetsoundedu

Present AddressdaggerRoanoke College Salem Virginia 24153 United States

Notes

The authors declare no competing financial interest

ACKNOWLEDGMENTSThis work was initiated with the support of the NationalScience Foundation CCLI-Adaptation and ImplementationProgram (0088633) The corresponding author thanks PaulMonaghan (University of Puget Sound) for his technicalassistance and the reviewers for their comments and ideas forfurther studies

REFERENCES(1) Guidelines for classifying coordination polymers networks andmetalminusorganic frameworks are provided in the following references(a) Batten S R Champness N R Chen X Garcia-Martinez JKitagawa S Ohrstrom L OrsquoKeeffe M Suh M P Reedijk JTerminology of metal-organic frameworks and coordination polymers(IUPAC Recommendations 2013) Pure Appl Chem 2013 85 (8)1715minus1724 (b) Batten S R Champness N R Chen X Garcia-Martinez J Kitagawa S Ohrstrom L OrsquoKeeffe M Suh M PReedijk J Coordination polymers metal-organic frameworks and theneed for terminology guidelines CrystEngComm 2012 14 (9) 3001minus3004(2) Cook T R Zheng Y Stang P J Metal-organic Frameworksand Self-assembled Supramolecular Coordination Complexes Com-paring and Contrasting the Design Synthesis and Functionality ofMetal-Organic Materials Chem Rev 2013 113 (1) 734minus777(3) (a) Thematic Issue Metal Organic Frameworks Chem Rev2012 112 (2) 673 minus 1268 (b) Themed Collection Metal OrganicFrameworks Chem Soc Rev 2009 38 (5) 1203minus1504 (c) ThemedCollection Coordination Polymers Structure and Function New JChem 2010 34 (11) 2353minus2681(4) Sumida K Arnold J Preparation Characterization andPostsynthetic Modification of Metal-Organic Frameworks SyntheticExperiments for an Undergraduate Laboratory Course in InorganicChemistry J Chem Educ 2011 88 (1) 92minus94(5) Rood J A Henderson K W Synthesis and Small MoleculeExchange Studies of a Magnesium Bisformate Metal-Organic Frame-work An Experiment in Host-Guest Chemistry for the UndergraduateLaboratory J Chem Educ 2013 90 (3) 379minus382(6) (a) Moskovitz C Kellogg D Inquiry-Based Writing in theLaboratory Course Science 2011 332 (6032) 919minus920 (b) AlaimoP J Bean J C Langenhan J M Nichols L Eliminating LabReports A Rhetorical Approach for Teaching the Scientific Paper inSophomore Organic Chemistry Writing Across Curric J 2009 20 17minus32(7) (a) Yaghi O M Li H Groy T L Construction of PorousSolids from Hydrogen-Bonded Metal Complexes of 135-Benzene-tricarboxylic Acid J Am Chem Soc 1996 118 (38) 9096minus9101(b) Yaghi O M Li H Davis C Richardson D Groy T LSynthetic Strategies Structure Patterns and Emerging Properties inthe Chemistry of Modular Porous Solids Acc Chem Res 1998 31 (8)474minus484(8) (a) Khan N A Haque E Jhung S H Rapid Synthesis of aMetal-Organic Framework Material Cu3(BTC)2(H2O)3 Under Micro-wave A Quantitative Analysis of Accelerated Synthesis Phys ChemChem Phys 2010 12 (11) 2625minus2631 (b) Diring S Furukawa STakashima Y Tsuruoka T Kitagawa S Controlled MultiscaleSynthesis of Porous Coordination Polymer in NanoMicro RegimesChem Mater 2010 22 (16) 4531minus4538 (c) Maniam P Stock NInvestigation of Porous Ni-Based Metal-Organic FrameworksContaining Paddle-Wheel Type Inorganic Building Units via High-Throughput Methods Inorg Chem 2011 50 (11) 5085minus5097(9) (a) Zeltmann A H Matwiyoff N A Morgan L O NuclearMagnetic Resonance of Oxygen-17 and Chlorine-35 in AqueousHydrochloric Acid Solutions of Cobalt(II) I Line Shifts and RelativeAbundances of Solution Species J Phys Chem 1968 72 (1) 121minus127 (b) Shakhashiri B S Chemical Demonstrations The University ofWisconsin Press Madison WI 1983 Vol 1 pp 280minus285 (c) OBrienJ J OrsquoBrien J F The Laporte Selection Rule in ElectronicAbsorption Spectroscopy J Coll Sci Teach 1999 29 (2) 138minus140

Journal of Chemical Education Laboratory Experiment

dxdoiorg101021ed5000839 | J Chem Educ XXXX XXX XXXminusXXXD

(105 degC) but this did not have a significant effect on the yieldor the phase purity of the material The microwave reactorproved to be the quickest most efficient method (30 min at 80degC) to produce Co3(BTC)2middot12H2O The most notabledifference between the Co3(BTC)2middot12H2O samples was thatdark pink crystals formed in the stainless steel vessel whereaspink powdery products were isolated by the other methodsonly the former method utilized a slow temperature cool downwhich tended to favor crystalline growthCharacterization

The Supporting Information provides IR TGA and XRD datacollected by students that demonstrate that Co3(BTC)2middot12H2Ois produced independent of the hydrothermal reactoremployed A unique characteristic of Co3(BTC)2middot12H2O isthat the sample undergoes a distinct change in color duringdehydration The fully hydrated sample is dark pink andtransitions through purple when partially dehydrated to bluewhen completely dehydrated This color change is similar tothat observed in humidity detection strips that are impregnatedwith hydrated cobalt(II) chloride the hydrated octahedralcomplex is pink whereas the (nearly) anhydrous cobalt(II)chloride tetrahedral complex is blue9

A thermogram of Co3(BTC)2middot12H2O collected by students(Figure 2) outlines the weight loss due to dehydration of the

coordinated water molecules At 100 degC the weight loss of25 corresponds to the loss of 11 water molecules performula unit and by 200 degC the weight loss corresponds to theloss of almost 115 H2O molecules The sample is fullydehydrated (minus12 H2O) above 290 degC which is lower thanreported7a this is likely due to different heating rates Becausethe only thermal event for Co3(BTC)2middot12H2O is loss of waterthe determination of the amount of water removed at aparticular temperature could be performed using traditionalgravimetric analysis methods with careful repetitive analyticalweighing before and after heating a sampleThe IR spectrum of Co3(BTC)2middot12H2O (Supporting

Information) matches that reported7a and can be comparedto that of the starting material (135-benzenetricarboxylic acid)The lack of the 1730minus1690 cmminus1 absorption band inCo3(BTC)2middot12H2O indicates that the BTC unit was deproto-nated to form carboxylate The broad absorption bandsbetween 3467minus3125 cmminus1 indicate the presence of water in

the complex and these absorption bands diminish with thepartial and complete dehydration of the complexPowder X-ray diffraction is utilized to determine the phase

purity of Co3(BTC)2middot12H2O as well to monitor thecrystallinity of the structure as the water molecules are partiallyor completely removed and reabsorbed Figure 3 shows

representative student-acquired powder XRD patterns ofCo3(BTC)2middot12H2O that highlight the changes in thecrystallinity during the partial dehydration and rehydrationprocess The lowest pattern in Figure 3 is obtained from theprepared Co3(BTC)2middot12H2O and indicates that the materialhas long-range atomic order with three low angle majorreflections at 173 184 and 267 2θ (deg) When the materialis partially dehydrated the broadening in the diffraction patternindicates that deformation in the crystalline lattice is occurring(Figure 3 middle patterns) Due to the lower intensity of thesediffraction patterns in comparison to the original product theyappear flat in the overlay however for a better view of thebroadening see Figure S8 in the Supporting Information Afterthe sample is rehydrated by soaking in water for 5minus10 min theoriginal diffraction pattern is nearly restored with only minorchanges in the position or intensity of the reflections (Figure 3top) A deformation in the crystalline latticeversus acomplete loss of crystallinityduring the partial dehydrationis supported because the rehydration process occurs instantlywithout the sample dissolving and recrystallizing Therehydration of partially dehydrated samples containing varyingamounts of water (Co2(BTC)3middot(1minus11)H2O) has beeninvestigated and in all cases the crystallinity of the frameworkis reestablished as determined by XRD However when acompletely dehydrated sample is rehydrated the originalstructure is not restored indicating a collapse in the structureand the loss of crystallinity in the framework (see Figure S10 inSupporting Information) Therefore the reversibility of thedehydrationminusrehydration process is contingent upon having atleast one water molecule (per formula unit) present as part ofthe framework to provide the hydrogen bonding interactionsnecessary to maintain the integrity of the framework Thisallows water molecules to reenter the voids that form duringdehydration To view the bonding students may refer to Figure1 (or the handout in Supporting Information) In order to view

Figure 2 Thermogram for Co3(BTC)2middot12H2O under a nitrogen flowwith a heating rate of 5 degCmin to 300 degC

Figure 3 Powder XRD patterns of Co3(BTC)2middot12H2O duringdifferent stages of dehydration and reabsorption of water The bottompattern (black) is for the ldquoas preparedrdquo sample synthesized via thestainless steel reactor the middle patterns are for partially dehydratedsamples Co3(BTC)2middot73H2O (purple) and Co3(BTC)2middot375H2O(blue) the top pattern (red) is for the fully rehydrated sample

Journal of Chemical Education Laboratory Experiment

dxdoiorg101021ed5000839 | J Chem Educ XXXX XXX XXXminusXXXC

the channels in the crystal structure students may refer to theoriginal article7 or they may obtain the crystallographicinformation file (cif) through the Cambridge StructuralDatabase and view on software made available from thesite10 This illustrates to students that the role of water in theCo3(BTC)2 framework is more than that of a guest it is criticalin stabilizing the framework (via hydrogen bonding)Guest dependent pore stability has been observed to a lesser

extent during the dehydration of different BTC-containingMOFs [M(HBTC)(H2O)2]middot05H2O (M = Sr or Ba)11

Although the resulting channels in [M(HBTC)(H2O)2]middot05H2O are almost double in size of Co3(BTC)2middot12H2O theobserved deformation of the former structure duringdehydration is minimal due to the fact that fewer watermolecules per cation are being liberated than in theCo3(BTC)2middot12H2O structure

SUMMARYCo3(BTC)2middot12H2O can be safely and effectively prepared byhydrothermal synthesis using a variety of reactors Thermog-ravimetric analysis provides the temperature range throughwhich dehydration occurs Structural changes to the frameworkthat occur during the partial dehydration and reabsorption ofthe included water molecules are monitored with powder X-raydiffraction With this experiment students learn new syntheticand instrumental techniques and integrate their findings inorder to explain factors that affect the reversibility of thedehydrationminusrehydration process of this MOF The studentsrsquolevel of understanding and ability to consider data frommultiple sources are mainly assessed through discussions withthem in the laboratory and by reading their journal-style Resultsand Discussion reportStudents have investigated the synthesis or the dehydration

process beyond the basic experiment and such further studieshave included optimizing the reaction conditions withalternative hydrothermal reactors12 to produce Co3(BTC)2middot12H2O investigating the inclusion of ammonia7a into a partiallydehydrated sample of Co3(BTC)2middotxH2O and the (hydro-thermal solvothermal or traditional) synthesis and character-ization of other metalminusBTC materials1113 These studies arebriefly outlined in the Supporting Information Although thisexperiment has been presented as an advanced experiment itcould be easily tailored to introduce inorganic materials andsimple gravimetric analysis at the introductory level

ASSOCIATED CONTENT

S Supporting Information

This section includes experimental details for students alongwith safety precautions instructor notes with purchasinginformation ideas for further studies and additional datacollected by students This material is available via the Internetat httppubsacsorg

AUTHOR INFORMATION

Corresponding Author

E-mail jcranepugetsoundedu

Present AddressdaggerRoanoke College Salem Virginia 24153 United States

Notes

The authors declare no competing financial interest

ACKNOWLEDGMENTSThis work was initiated with the support of the NationalScience Foundation CCLI-Adaptation and ImplementationProgram (0088633) The corresponding author thanks PaulMonaghan (University of Puget Sound) for his technicalassistance and the reviewers for their comments and ideas forfurther studies

REFERENCES(1) Guidelines for classifying coordination polymers networks andmetalminusorganic frameworks are provided in the following references(a) Batten S R Champness N R Chen X Garcia-Martinez JKitagawa S Ohrstrom L OrsquoKeeffe M Suh M P Reedijk JTerminology of metal-organic frameworks and coordination polymers(IUPAC Recommendations 2013) Pure Appl Chem 2013 85 (8)1715minus1724 (b) Batten S R Champness N R Chen X Garcia-Martinez J Kitagawa S Ohrstrom L OrsquoKeeffe M Suh M PReedijk J Coordination polymers metal-organic frameworks and theneed for terminology guidelines CrystEngComm 2012 14 (9) 3001minus3004(2) Cook T R Zheng Y Stang P J Metal-organic Frameworksand Self-assembled Supramolecular Coordination Complexes Com-paring and Contrasting the Design Synthesis and Functionality ofMetal-Organic Materials Chem Rev 2013 113 (1) 734minus777(3) (a) Thematic Issue Metal Organic Frameworks Chem Rev2012 112 (2) 673 minus 1268 (b) Themed Collection Metal OrganicFrameworks Chem Soc Rev 2009 38 (5) 1203minus1504 (c) ThemedCollection Coordination Polymers Structure and Function New JChem 2010 34 (11) 2353minus2681(4) Sumida K Arnold J Preparation Characterization andPostsynthetic Modification of Metal-Organic Frameworks SyntheticExperiments for an Undergraduate Laboratory Course in InorganicChemistry J Chem Educ 2011 88 (1) 92minus94(5) Rood J A Henderson K W Synthesis and Small MoleculeExchange Studies of a Magnesium Bisformate Metal-Organic Frame-work An Experiment in Host-Guest Chemistry for the UndergraduateLaboratory J Chem Educ 2013 90 (3) 379minus382(6) (a) Moskovitz C Kellogg D Inquiry-Based Writing in theLaboratory Course Science 2011 332 (6032) 919minus920 (b) AlaimoP J Bean J C Langenhan J M Nichols L Eliminating LabReports A Rhetorical Approach for Teaching the Scientific Paper inSophomore Organic Chemistry Writing Across Curric J 2009 20 17minus32(7) (a) Yaghi O M Li H Groy T L Construction of PorousSolids from Hydrogen-Bonded Metal Complexes of 135-Benzene-tricarboxylic Acid J Am Chem Soc 1996 118 (38) 9096minus9101(b) Yaghi O M Li H Davis C Richardson D Groy T LSynthetic Strategies Structure Patterns and Emerging Properties inthe Chemistry of Modular Porous Solids Acc Chem Res 1998 31 (8)474minus484(8) (a) Khan N A Haque E Jhung S H Rapid Synthesis of aMetal-Organic Framework Material Cu3(BTC)2(H2O)3 Under Micro-wave A Quantitative Analysis of Accelerated Synthesis Phys ChemChem Phys 2010 12 (11) 2625minus2631 (b) Diring S Furukawa STakashima Y Tsuruoka T Kitagawa S Controlled MultiscaleSynthesis of Porous Coordination Polymer in NanoMicro RegimesChem Mater 2010 22 (16) 4531minus4538 (c) Maniam P Stock NInvestigation of Porous Ni-Based Metal-Organic FrameworksContaining Paddle-Wheel Type Inorganic Building Units via High-Throughput Methods Inorg Chem 2011 50 (11) 5085minus5097(9) (a) Zeltmann A H Matwiyoff N A Morgan L O NuclearMagnetic Resonance of Oxygen-17 and Chlorine-35 in AqueousHydrochloric Acid Solutions of Cobalt(II) I Line Shifts and RelativeAbundances of Solution Species J Phys Chem 1968 72 (1) 121minus127 (b) Shakhashiri B S Chemical Demonstrations The University ofWisconsin Press Madison WI 1983 Vol 1 pp 280minus285 (c) OBrienJ J OrsquoBrien J F The Laporte Selection Rule in ElectronicAbsorption Spectroscopy J Coll Sci Teach 1999 29 (2) 138minus140

Journal of Chemical Education Laboratory Experiment

dxdoiorg101021ed5000839 | J Chem Educ XXXX XXX XXXminusXXXD

the channels in the crystal structure students may refer to theoriginal article7 or they may obtain the crystallographicinformation file (cif) through the Cambridge StructuralDatabase and view on software made available from thesite10 This illustrates to students that the role of water in theCo3(BTC)2 framework is more than that of a guest it is criticalin stabilizing the framework (via hydrogen bonding)Guest dependent pore stability has been observed to a lesser

extent during the dehydration of different BTC-containingMOFs [M(HBTC)(H2O)2]middot05H2O (M = Sr or Ba)11

Although the resulting channels in [M(HBTC)(H2O)2]middot05H2O are almost double in size of Co3(BTC)2middot12H2O theobserved deformation of the former structure duringdehydration is minimal due to the fact that fewer watermolecules per cation are being liberated than in theCo3(BTC)2middot12H2O structure

SUMMARYCo3(BTC)2middot12H2O can be safely and effectively prepared byhydrothermal synthesis using a variety of reactors Thermog-ravimetric analysis provides the temperature range throughwhich dehydration occurs Structural changes to the frameworkthat occur during the partial dehydration and reabsorption ofthe included water molecules are monitored with powder X-raydiffraction With this experiment students learn new syntheticand instrumental techniques and integrate their findings inorder to explain factors that affect the reversibility of thedehydrationminusrehydration process of this MOF The studentsrsquolevel of understanding and ability to consider data frommultiple sources are mainly assessed through discussions withthem in the laboratory and by reading their journal-style Resultsand Discussion reportStudents have investigated the synthesis or the dehydration

process beyond the basic experiment and such further studieshave included optimizing the reaction conditions withalternative hydrothermal reactors12 to produce Co3(BTC)2middot12H2O investigating the inclusion of ammonia7a into a partiallydehydrated sample of Co3(BTC)2middotxH2O and the (hydro-thermal solvothermal or traditional) synthesis and character-ization of other metalminusBTC materials1113 These studies arebriefly outlined in the Supporting Information Although thisexperiment has been presented as an advanced experiment itcould be easily tailored to introduce inorganic materials andsimple gravimetric analysis at the introductory level

ASSOCIATED CONTENT

S Supporting Information

This section includes experimental details for students alongwith safety precautions instructor notes with purchasinginformation ideas for further studies and additional datacollected by students This material is available via the Internetat httppubsacsorg

AUTHOR INFORMATION

Corresponding Author

E-mail jcranepugetsoundedu

Present AddressdaggerRoanoke College Salem Virginia 24153 United States

Notes

The authors declare no competing financial interest

ACKNOWLEDGMENTSThis work was initiated with the support of the NationalScience Foundation CCLI-Adaptation and ImplementationProgram (0088633) The corresponding author thanks PaulMonaghan (University of Puget Sound) for his technicalassistance and the reviewers for their comments and ideas forfurther studies

REFERENCES(1) Guidelines for classifying coordination polymers networks andmetalminusorganic frameworks are provided in the following references(a) Batten S R Champness N R Chen X Garcia-Martinez JKitagawa S Ohrstrom L OrsquoKeeffe M Suh M P Reedijk JTerminology of metal-organic frameworks and coordination polymers(IUPAC Recommendations 2013) Pure Appl Chem 2013 85 (8)1715minus1724 (b) Batten S R Champness N R Chen X Garcia-Martinez J Kitagawa S Ohrstrom L OrsquoKeeffe M Suh M PReedijk J Coordination polymers metal-organic frameworks and theneed for terminology guidelines CrystEngComm 2012 14 (9) 3001minus3004(2) Cook T R Zheng Y Stang P J Metal-organic Frameworksand Self-assembled Supramolecular Coordination Complexes Com-paring and Contrasting the Design Synthesis and Functionality ofMetal-Organic Materials Chem Rev 2013 113 (1) 734minus777(3) (a) Thematic Issue Metal Organic Frameworks Chem Rev2012 112 (2) 673 minus 1268 (b) Themed Collection Metal OrganicFrameworks Chem Soc Rev 2009 38 (5) 1203minus1504 (c) ThemedCollection Coordination Polymers Structure and Function New JChem 2010 34 (11) 2353minus2681(4) Sumida K Arnold J Preparation Characterization andPostsynthetic Modification of Metal-Organic Frameworks SyntheticExperiments for an Undergraduate Laboratory Course in InorganicChemistry J Chem Educ 2011 88 (1) 92minus94(5) Rood J A Henderson K W Synthesis and Small MoleculeExchange Studies of a Magnesium Bisformate Metal-Organic Frame-work An Experiment in Host-Guest Chemistry for the UndergraduateLaboratory J Chem Educ 2013 90 (3) 379minus382(6) (a) Moskovitz C Kellogg D Inquiry-Based Writing in theLaboratory Course Science 2011 332 (6032) 919minus920 (b) AlaimoP J Bean J C Langenhan J M Nichols L Eliminating LabReports A Rhetorical Approach for Teaching the Scientific Paper inSophomore Organic Chemistry Writing Across Curric J 2009 20 17minus32(7) (a) Yaghi O M Li H Groy T L Construction of PorousSolids from Hydrogen-Bonded Metal Complexes of 135-Benzene-tricarboxylic Acid J Am Chem Soc 1996 118 (38) 9096minus9101(b) Yaghi O M Li H Davis C Richardson D Groy T LSynthetic Strategies Structure Patterns and Emerging Properties inthe Chemistry of Modular Porous Solids Acc Chem Res 1998 31 (8)474minus484(8) (a) Khan N A Haque E Jhung S H Rapid Synthesis of aMetal-Organic Framework Material Cu3(BTC)2(H2O)3 Under Micro-wave A Quantitative Analysis of Accelerated Synthesis Phys ChemChem Phys 2010 12 (11) 2625minus2631 (b) Diring S Furukawa STakashima Y Tsuruoka T Kitagawa S Controlled MultiscaleSynthesis of Porous Coordination Polymer in NanoMicro RegimesChem Mater 2010 22 (16) 4531minus4538 (c) Maniam P Stock NInvestigation of Porous Ni-Based Metal-Organic FrameworksContaining Paddle-Wheel Type Inorganic Building Units via High-Throughput Methods Inorg Chem 2011 50 (11) 5085minus5097(9) (a) Zeltmann A H Matwiyoff N A Morgan L O NuclearMagnetic Resonance of Oxygen-17 and Chlorine-35 in AqueousHydrochloric Acid Solutions of Cobalt(II) I Line Shifts and RelativeAbundances of Solution Species J Phys Chem 1968 72 (1) 121minus127 (b) Shakhashiri B S Chemical Demonstrations The University ofWisconsin Press Madison WI 1983 Vol 1 pp 280minus285 (c) OBrienJ J OrsquoBrien J F The Laporte Selection Rule in ElectronicAbsorption Spectroscopy J Coll Sci Teach 1999 29 (2) 138minus140

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(10) The Cambridge Crystallographic Data Centre (CCDC) httpwwwccdccamacuk (accessed Mar 2013)(11) Plater M J Roberts A J Marr J Lachowski E E Howie RA Hydrothermal Synthesis and Characterisation of Alkaline-EarthMetal Salts of Benzene-135-Tricarboxylic Acid J Chem Soc DaltonTrans 1998 5 797minus802(12) Schlesinger M Schulze S Hietschold M Mehring MEvaluation of Synthetic Methods for Microporous Metal-organicFrameworks exemplified by the Competitive Formation of[Cu2(BTC)3(H2O)3] and [Cu2(BTC)(OH)(H2O)] MicroporousMesoporous Mater 2010 132 (1minus2) 121minus127(13) (a) Yaghi O M Davis C E Li G Li H Selective GuestBinding by Tailored Channels in a 3-D Porous Zinc(II)-Benzene-tricarboxylate Network J Am Chem Soc 1997 119 (12) 2861minus2868(b) Srinivasan B R Shetgaonkar S Y Raghavaiah P Soft Synthesisof a Metal-organic Framework based on a Tribarium Building BlockIndian J Chem 2012 51A (8) 1064minus1072

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