Synthesis of cobalt and iron-based metal-organic frameworks and their applications

1.1 DefinitionofMetalorganicframeworksMOFs MOFsisthecompoundwhichareconsistedofmetalclustersandlinker,typically,polytopicorganiccarboxylateswasemployed,forexample,1,4- benzenedicarboxyli

Abstract

Thesynthesis,structuralidentificationoffournovelcobaltandiron-b a s e d metal-organicframeworks( M O F s ) , namedVNU-10(coThesynthesis,structuralidentificationoffournovelcobaltandiron-balt-basedMOF),VNU-15(iron-

Hcouplingswhileapreviouslyreportedtopologicalisomer,Co2(BDC)2(DABCO)sqldisplayedp o o r activityu n d e r testingcondition.Leachingtestsindicatedthathomogeneouscatalysisvialeachedactivecobaltspeciesisunlikely.Furthermore,theVNU-

10catalystwasfacilelyisolatedfromt h e reactionmixturea n d reusedseveraltimeswithoutdegradationofthecatalyticreactivity

Furthermore,VNU-

15withintegratedsulphateligandsaccompaniedbyhydrogen-bondeddimethylammoniumionsthatlinedtheporechannels,theprotonconductivityofthismaterialreached2.90×10-2Scm-

1at95°Cand6 0 % relativehumiditywhichi s r o u g h l y 2.5timeshigherthannafionundersimilarconditions(1.0×10-2Scm-

1at60%RHand80°C)ando n theorderofamagnitudehigher

thanthatobservedinseveralof

thehighestperformingMOFsreported,albeitthesematerials’protonconductivitypropertieswerer ep o rt ed w it h highworkingrelativ e humidity(RH≥90%).Remarkably,theultrahighprotonconductivityofVNU-

15wasmaintainedundertheseconditions,withoutanyappreciableloss,for40hours

1.1 DefinitionofMetalorganicframeworks(MOFs)

MOFsisthecompoundwhichareconsistedofmetalclustersandlinker,typically,polytopicorganiccarboxylateswasemployed,forexample,1,4-

benzenedicarboxylicacid (H2dimensionalstructureswhichcanbeporous(Figure1)

BDC),toconstructtwo-,orthree-Fig.1StructureofMOF-5constructedfromZn4O(CO2)6clusterandBDC

1.2 ApplicationsofMOFsasHeterogeneousCatalysis

Catalysts,generally,wereclassifiedi n t o homogenousandheterogeneous,inwhich,thehomogenouscatalystswererecognizedforfastkineticandhighconversioninorganicsynthesis,albeit,severaldrawbackshaveb e e n accountedf o r , whichincludingt h e difficultiest o separatethecatalystsforrecyclinginvestigationsaswellasdesiredproductswereusuallycontaminatedbycatalystordecomposedproductsofcatalyst.Ontheotherh a n d , heterogeneouscatalystwasrecognizedasgreenerpathwayfororganicsynthesisowningtoitsconvenienceforrecycling,inwhich,thecatalystscanb e easily separatedfromthereactionmixture.Despitesignificantadvantageo f heterogeneouscatalysts,organicsynthesisemployedthesecatalysts,mostlyresultedinlowconversion,hence,oneofinterestingresearchdirectioninthecatalyticfieldhasbeendevotedtodevelopmoreefficientlyheterogeneouscatalysts

Traditionalheterogeneouscatalystsincludemetaloxides,polymerresin,silicagelandzeolites,forwhich,lowsurfaceareaofmetaloxides,polymerresina s wellast h e smallporeapertureofzeolite,p r e v e n t i n g t h e largeorganicsubstratesfromreachingcatalyticcenters,thuslimitingtheusefort h e transformationoflargeorganicsubstrates.Anotherplatform,mesoporoussilicagel,whichpossessedlargeporeandhighsurfacearea,however,thestructureandporesizeo f t h e materialsarenotuniforma n d t h e immobilizationofactivecenterswithinitsporehasmaintainedchallenges.

Oxidativetransformationoflargeorganicsubstrates,commonlyrequiredt h eformationofactiveradicalsorhighoxidationstateofthemetalcenters,whichisunstablewithveryshortdecaytime,hencerequiredfastdiffusiono f organicsubstrateontothecatalyticactivesites.Recently,MOFshavebeenemployeda s t h e platformf o r catalyticsynthesiso f diverseorganiccompounds.Inf a c t , mosto f publishedMOFspossessedthesmallporeaperturewithlowsurfacearea(lessthan8Åand2000m2g-

1),someofmostnoticeableMOFshavelargeinternalsurfaceareasandultralowdensities.7Duet o thelargea n d uniformp o r e sizeanddefinitelycoordinativeenvironmentofmetalactivecenters,afewMOFscatalystsexhibitedinterestingpropertiesforoxidativetransformationoflargeorganicsubstrates,however,theexamplesfortheseclassofcatalyticreactionsarestillveryrare

y componentswithinH F C s ) couldnotwells u p p o r t fora b o v e workingcondition,hence,thequesttosynthesizePEMFCswhichcansatisfactorilyf u n c t i o n atmediumtemperature(T≥100°C)underlowRHwasraisedastopurgentgoal

Recently,metal-organicframeworks(MOFs)havebeenexploredaspotentialcandidatesforuseaselectrolytematerials.ThisisprimarilyduetothemodularnatureofMOFdesignandsynthesis,i n w h i c h thebackbone

e a c i d i t y o f t h e p o r e c h a n n e l s t h r o u g h incorporatingspecificfunctionalgroupsandcontrollingandmod i fy in g defectsitesamongothers.Thesestrategieshavel e d t o significantd e v e l o p m e n t a l progress,inwhichprotonconductivitiesinMOFshavebeenachievedontheorderof10-2Scm-

1,butrequirehighworkingrelativehumidity(≥9 0 % RH).Ontheotherhand,protonconductivityunderanhydrous conditions (T

≥1 0 0 °C)i n MO F s hasr e a c h e d ultrahighl e v e l s (10-2S

Chapter2:SynthesisoftheNovelMetal-OrganicFrameworksandCharacterizations

2.1 Introduction

TheQuestofNovelMOFswithEnhancedPropertiesf o r SustainableApplica tions

TheHighporosityo f MOFsa s wellast h e m o d u l a r n a t u r e o f M O F d

e s i g n a n d s y n t h e s i s , i n w h i c h t h e b a c k b o n e c o m p o n e n t s [ e g i n

o r g a n i c a n d o r g a n i c s e c o n d a r y b u i l d i n g u n i t s ( S B U s ) ] , c

a n b e e a s i l y t a i l o r e d , MOFsispromisedfordiversifiedapplicationssuchasgasstoragea n d separation,catalysts,protonconduction,sensor,lightharvest,drugdelivery,batteriesandsupercapacitors,andsoon

Recently,morethan

20.000differentMOFshavebeenreported.Severalo f thesewerefoundtohavethecapabilitiestosolvechallengewhichencounteredinmodernages.DespitethesignificantprogressinsynthesisandapplicationsofMOFs,therearemaintainedchallengessoughttoovercomeb y novelMOFs,whichpossessnovelorenhancedproperties,forexample,t h e questtosynthesizebetterprotonconductingmembranethatcanmaintainhighconductivity(>10-2Scm-

1)atmediumtemperature(T≥100°C)orademandf o r largerporeapertureporousmaterialwhichc a n servea s hostscaffoldforvariousdopingofactiveguestmoleculesaswellasplayedthecatalystforthetransformationoflargeorganicsubstrates

Inlasttwodecades,avastnumberofMOFshavebeensynthesizedfromt h e cheapandcommerciallinkers,takennotices,oursurveyinCambridgestructuraldatabasegaveapproximately5 0 9 2 s t r u c t u r e s , i n whichterephthalicacid(H2BDC)wasfoundtobethekeyconstructedcomponent.However,i n respectingt o c h e a

p costforconsequentvastproduction,ins c o p e ofexploration,ourtargetsemployedthecheapandcommerciallinkersa s wellasearthabundantmetalssuchasironandcobalttosynthesizethenovelmetal-

organicframeworks.Subsequently,o u r newlydiscoveredcrystalstructurewereemployeda s standpointsforinitiallyjustifyingtheinterestingpropertiesofnovelMOFsinordertoemployi nrelevantapplications

acid(H3BTC);aminoterephthalicacid(NH2-H2BDC)a n d

1,6-naphthalenedicarboxylicacid(H2NDC).Inf a c t , therearemaintainedvastmajorityofunexploredsyntheticconditions,i n whicht h e mixtureo f s e v e r a l organicbuildingblocks,incorporatingvariousmetalsources,havebeencarriedoutyettosynthesizemetal-organicframeworks

Hence,weemployedsinglelinkeraswellasthemixedlinkerstrategy,whichincorporatedwithcobaltandironmetalsourcestoapproachdiversenovelmetal-organicframeworkswhichpossesstheenhancedornovelproperties,i n whichthe

heatedat120°Ci n anisothermalovenfor12h.Aftercoolingthevialstoroomtemperature,t h e solidproductwasremovedb y decantingt h e motherliquora n d t h e nwashedwithDMF(3×10mL)toremoveanyunreactedspecies.TheDMFsolventwasexchangedwithdichloromethane(DCM)

(3×10mL)atroomtemperature.Theproductwasthendriedat120°Cfor4hundervacuum,yieldinggreenneedle-shapedcrystalsofVNU-

10(76%basedonCo(NO3)2·6H2O)

(Scheme4 ) EA:Calcd.f o r C o2C22H26O11N2=[Co2(BDC)2(DABCO)]∙3H2O:C,43.15;H,4.28;N,4.58%.Found:C,43.19;

H,4.35;N,4.50%.AASindicatedcobaltamountof20.0%,whichmatchedwithcalculatedvalueof20.9%

Scheme1Syntheticschemeforcrystallizinggreen,needleVNU-10.

2.2.2 StructureofnovelCo 2 (BDC) 2 (DABCO) kgm

NovelcobaltMOF,namedCo2(BDC)2(DABCO)

kgm(VNU-10),

hasbeensynthesized.SingecrystalX-raydiffractionrevealedthelargeporeaperturea n d 10(14 Åporewindow)(Figure2)

FullcharacterizationofVNU-XRDandPXRD,respectively),Elementalanalysis(EA),Fouriertransforminfraredspectroscopy(FT-

10hasbeendone,whichincludingsingleandpowderX-raydiffraction(SC-IR),thermogravimetricanalysis(TGA),atomicabsorptionspectroscopy(AAS),inductivelycoupledplasmamassspectroscopy(ICP-MS)a n d gasesadsorption

Fig.3N2adsorptionisothermofVNU-10at77K.

thendividedbetweensixborosilicateglasstubes( 1 7 mLe a c h t u b e ) The glasstubesweresubsequentlyflamesealedunderambientconditionsandplacedinanisothermaloven,preheateda t 165°C,forfourdaystoyieldreddish-

yellowcrystalsofVNU-15.Thesecrystalswerewashedwith10mLDMF( 6 times)andimmersedi n DMFthreedaysbeforeexchangingthesolventwith10mLDCMovertwodays(6timesforexchangingsolvent).Thereafter,VNU-

Fig.9 CrystalstructureofVNU-15i s constructedfromBDC2-andNDC

2-linkersthats t i t c h togethercorrugatedinfiniterodsof

[Fe2(CO2)3(SO4)2(DMA)2]∞(a ) T h e s e corrugatedinfiniterodspropagatealong

theaandbaxest o

formthethree-dimensionala r c h i t e c t u r e T h e structureisshownfromthe[110]and[001]pla

ns(b,c,respectively).RepresentationofthefobtopologythatVNU-15adopts(d,e ) A t o m colours:Fe,orangeandbluepolyhedra;C,black;O,red;S,yellow;N,blue;andDMAcations, lightblue.AllotherHatomsareomittedforclarity

Singlec r y s t a l

X-

raydiffraction(SCXRD)analysisrevealedthatVNU-15crystallizedintheorthorhombicspacegroup,Fddd(No.70),withunitcell parameters,a=16.7581,b=18.8268,andc=38.9998Å.Thearchitectureof

VNU-15isbasedontwodistinctlinkers,namelyBDC

2-andNDC2-,thats t i t c h togethercorrugatedi r o n infiniter o d SBUs.Theseinfiniter o d SBUs,formulateda s Fe2(CO2)3(SO4)2(DMA)2]∞,arecomposedo f twoindependentoctahedralironatomsthatalternateconsecutivelyinorder(Figure9a).Thecoordinationenvironmentofeachdistinctironatomishighlightedb y twoequatorialcorner-sharingverticesderivedfromμL,0.24μmol).The2-Oatomsofthecarboxylatefunctionalityi n NDC2-.I t i s notedt h a t theseμL,0.24μmol).The

-Oatoms,whicharecistooneanother,arewhatpromotetheinfiniterodSBUt

oarrangei n a corrugatedfashion.Thecoordinationsphereof

eachironisthencompletedthroughbridgingaxialsulphateligandsandb r i d g

i n g carboxylatefunctionalitiesfromBDC2-(Figure9a).TwoBDC andoneNDC2-linkers,relativelyclosetogetherinspace(aromaticπ–

2-πinteractiondistance,3.4Å),connectinfiniter o d s togetherperiodicallyinaperpendicularmanner(83.4°)(Figure9band9 c ) Thispropagatesathree-

withtheaxialbridgingsulphateligands(N-H···O-2.3.3

CharacterizationsofNovelAnionicFe-basedMetal-OrganicFramework

IR,TGA,AAS,waterandgasesadsorptionhavebeendone

FullcharacterizationofVNU-15,whichincludingSC-XRD,EA,PXRD,FT-WaterisothermofVNU-15wasmeasuredbyBELSORP-aqua3

AmixtureofNH2-H2BDC(0.13g,0.73mmol),FeSO4·7H2O(0.13g,0.49mmol),CuCl2·2H2O(0.13g,0.76mmol),9,10-anthraquinone(0.02g,

0.095)wereweighedinabottleandDMF(15ml)wasadded,thereafter,theheterogeneoussolutionwassonicated10minutestogetthehomogeneouslya n d transferredintothreeautoclaves.Themixturewasheatedinovenat165

°Cfor72h.theresultingyellowsquareplatecrystalofFe-NH2

BDCwascollectedandwashedwithDMF(6times).Fe-NH2BDCwasexchangedwithd r y DCMfor24h(6times)thenheatedatroomtemperatureunderdynamicvacuumfor 12hourstoobtainofFe-NH-

BDC(0.102g56%yieldbasedonF e ) Note:withoutCuCl2·2H2Oor anthraquinone, MIL-88Bformed(Scheme3)

N H2BDCrepresentsi n s q l l a y e r s A t o m color: C,b l a c k ; O , r e d ; F e , orangepo

lyhedra;S , yellow;N,blue;Hof nitrogen,white;Hatomsconnectedtocarbonareomittedforclarity

ThestructureofFe-NH2BDCwasalsosolvedbysinglecrystalXRD,whichcrystallizedinI41/ amdspacegroupwiththeunitcellparametera=

2-adjacentSO4 arebridgedbyDMAwithN-H···OSdistancesof2.148Åtoform2Dstructure(Figure11bandc)

1 6 5

°Cfor72hours,theresultingreddish-yellowcubecrystalofFe-

BTCwascollectedandexchangedwithDMFovernight(6times).Thereafter,Fe-B T C wasexchangedwithdryDCMfor24h(6times)thenheatedat100°Cu n d e rdynamicvacuumfor12hourstoobtainactivatedFe-

angularBTClinkertoexpandintothemmm-aarchitecturewhichconsistedo f smalloctahedroncagea n d largecuboctahedro

ncage,whichsharedtriangularface(Figure12bandc).Thesulphateligandswere

foundtocapapicalsitesofironpaddlewheelSBUs,anotherfreechelateoxygensofsulphateligandswerefoundtopointtowardspaceinsidesmalloctahedroncageof

clustersplayedt h e catalyticactivesitesinMOFs,oncontrast,theactivesiteswereanchoredi n t o MOFsframeworkviathelinkersbeforetheself-assembly,post-

modification,orimmobilizedguestintotheporeduringself-assembly.Consequently,smallmoleculesiseasytoenterporeofMOFsinorderforthereactiontobeproceeded,howeverrelativesmallporesizelimitedcatalyticconversiono f largeorganicmoleculeswhichcommonlyd e s i r e d i n pharmaceuticalindustryasthesubstratecannoteffectivelyreachestheactivesiteswhichlocateinsideMOFsstructure

Indeed,theporesizeofMOFscouldbeexpandedbychoselongerlinkersi n

a n efforttoproducelargerporestructurewithhighersurfacearea Onthecontrast,theprocesshaditsowndrawbacks,whichbelongtocomplicatedorganicsynthesisa n d t h e resultedstructureusuallyinterpenetrated,thatsignificantlyreducedtheporesize,additionally,largerporesizepotentiallyleadedtostructurecollapseunderactivatedcondition

LargeporewindowandhighsurfaceareaMOFs(above14Å,2600m

2g-1)whichconstructedfromcheapandcommerciallyavailablelinkerssucha s benzenedicarboxylicacid(H2BDC)a n d 1,4-

1,4-Diazabicyclo[2.2.2]octane(DABCO)arerare,infact,onlyfewMOFsmatchedcriteria,forexamples,MIL-101,MIL-

68,Zn2(BDC)2DABCOkgm,a n dNi2(BDC)2DABCOkgm,

Hence,thequestfordesigningandsynthesizinglargeporewindowandhighsurfaceareaMOFsfromcheaplinkerandclarifyingtheadvantagesoflargeporesizeMOFcomparedwithsmallporesizeornonporousmaterialo n specificcatalyticreactionsforlargesubstrateswereraised

DirectAminationofAzolesunderMildReactionConditions

Moleculescontainingaryl-andheteroarylaminemoietiesarefrequentlyf o u n d inavarietyofbiologicallyactivenaturalproducts,polymers,aswella s functionalmaterials.Traditionalroutes

t o accessthesemoleculesmostoftenemploynitrenoidchemistry.SincethepioneeringworkbyBuchwalda n d Hartwig,metal-mediatedC-

NbondformationdirectlyfromC-Hbondshaveattractedanincreasingamountofinterest.Toperforms u c h transformations,nitrogenmoietieshavebeencommonlyinstalledbyusingprotectedaminesorhydroxylaminederivativesasstarting

materials.Simpleaminecouplingpartnersemployedi n

directC-Nb o n d formationofunfunctionalizedarenesorheterocycliccompoundshaverarelybeenreported.Typically,palladiumandrhodiumwereexploitedascatalystsforthesetransformations,mostlyintheintramolecularfashion

workerswereabletodirectoxidativeaminationofa varietyo f azolesi n thepresenceofa peroxideoxidant(Scheme5).Despitet h e significantprogressthathasbeenmadetowarddevelopinghighlyactivehomogeneouscatalysts,thedevelopmentofmoreeconomicallyandenvironmentallyefficientprotocols,mostnotablybyusingheterogeneouscatalyticsystems,forthistransformationhasyettobereported.

Objective

Highlighttheadvantageofobtainedcobaltbased-MOFwiththelargep o r e sizeandhighsurfaceareacanbeahighlyactiveheterogeneouscatalystf o r chemicaltransformationoflargeorganicmoleculeswhichcannotbedoneb y smallerporesizeMOFs