Design, structural diversity and properties of nov

DaltonTransactionsAninternationaljournalofinorganicchemistryrsc.li/daltonISSN1477-9226PAPERMarioWriedtetal.Design,structuraldiversityandpropertiesofnovelzwitterionicmetal–organicframeworksVolume46Number217June2017Pages6801–7108DaltonTransactionsPAPERCitethis:DaltonTrans.,2017,46,6853Received24thJanuary2017,Accepted3rdMarch2017DOI:10.1039/c7dt00292krsc.li/daltonDesign,structuraldiversityandpropertiesofnovelzwitterionicmetal–organicframeworks†DarpandeepAulakh,AnthonyP.Nicoletta,JoshuaB.Pyser,JubyR.VargheseandMarioWriedt*Sevennewzwitterionicmetal–organicframeworks(ZWMOFs)ofcompositions{[Cd(L1)(OH2)]·2H2O}n(1),{[Mn(L1)(OH2)2]·H2O}n(2),{[Cu(HL1)2(OH2)3]·9H2O}n(3),{[Mn2(L2)2(OH2)4]·3H2O}n(4),[Co(L2)(OH2)4]·H2O(5),[Ni(L2)(OH2)3]n(6),and{[Cd(L2)(OH2)3]·4H2O}n(7),whereH3L1Br=3-carboxy-1-(3,5-dicarboxy-benzyl)pyridiniumbromideandH3L2Br=4-carboxy-1-(3,5-dicarboxybenzyl)pyridiniumbromide,havebeensynthesizedunderhydrothermalconditions.WedemonstratethatthediversityofthesecrystalstructuressuggeststhatthetridentateandflexiblenatureofZWligandsL1andL2makethemexcellentcandidatesforthesynthesisofnewZWMOFs.Amulti-chargedanionicnatureisacommonfeatureofL1andL2,andtherefore,allowstherationaldesignofZWMOFswithoutthepresenceofadditionalcounterionsforchargecompensation.Allmaterialswerestructurallycharacterizedbysingle-crystalX-raydiffractionandfurthercharacterizedbyelementalanalyses,infraredspectroscopy(IR),powderX-raydiffraction(PXRD),thermogravimetricanalyses(TGA),differentialscanningcalorimetry(DSC)andadsorptionmeasurements.Mostinterestingly,permanentporositycouldbeobservedfor1,originatedfrom4Åchannelporesandconfirmedbymethanoladsorptionexperiments,whichyieldedanuptakeof7.43wt%at25°C;andrespectively,anhydratesof1,2,4and6canberehydrateduponexposuretoambientair,asevidencedbyTGAandPXRDmeasurements.Inaddition,wereportanin-depthCSDanalysisofselectedstructuralparameters,coordinationmodesandtopologiesexhibitedbyMOFsbasedonZWligandsL1andL2alongwiththeregio-isomericanalogueL3,whereH3L3Br=N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridiniumbromide.IntroductionOverthepastfewdecades,synthesis,crystalstructuresandpropertiesofmetal–organicframeworks(MOFs)havebeenwidelyresearched.Theseporousmaterials,composedofmetalclustersandpolytopicorganiclinkers,canbetailoredtospecificneedsbecauseoftheirstructuralandfunctionaltun-ability,afeaturethatisnotavailablewithconventionalporousmaterials(e.g.,zeolites,activatedcarbons).1–3This“tunability”allowsforvariousapplications,suchasgasstorage,chemicalseparation,sensingandcatalysis,4–18withafocusonCO2captureinourlaboratory.19–25WepreviouslyreportedanewdesignstrategyforaccessingMOFsbuiltfromzwitterionic(ZW)ligandswithadsorptionpropertiesbasedonmulti-pointhostguestinteractions.26,27Inacontinuationofthiswork,wesynthesizedthenewpyridiniumbasedmultichargedanionicZWligand,H3L1Br=3-carboxy-1-(3,5-dicarboxybenzyl)pyridi-niumbromide(Fig.1).ThepositivelychargedpyridiniumcenterisknowntopotentiallyenhanceinteractionswithgasFig.1LewisstructuresofligandL1andregio-isomericligandsL2andL3.†Electronicsupplementaryinformation(ESI)available:NMRdataofMe2HL1,H3L1,Me2HL2andH3L2;IRdataofH3L1,1and2;IRdataofH3L2,4,and6;PXRDpatternsforphasepure1,2,4,and6;temperatureellipsoidplotsforMOFs1–7,coordinationnetworksexhibitinghydrogenbondinginteractions,characteristicbonddistancesandanglesresponsibleforintraandinter-molecularhydrogenbondinginteractionsfor1–7;heatingratedependentTGAmeasurementsonMOFs2and4;PXRDpatternfordehydrated4′andrehydrated4″uponexposuretoregularair.CCDC1428987–1428992and1428994.ForESIandcrystallographicdatainCIForotherelectronicformatseeDOI:10.1039/c7dt00292kDepartmentofChemistry&BiomolecularScience,ClarksonUniversity,8ClarksonAve,Potsdam,NY13699,USA.E-mail:[e-mail];Fax:[phone];Tel:[phone]Thisjournalis©TheRoyalSocietyofChemistry2017DaltonTrans.,2017,46,6853–6869|6853Publishedon09March2017.Downloadedon04/07/201711:33:02.ViewArticleOnlineViewJournal|ViewIssuemolecules,12andthus,frameworksbasedonpyridiniumcar-boxylateligandshavebeendeployedforvariousapplicationssuchasgasadsorption,sensingetc.28–31Inaddition,ZWligandL1permitstherationaldesignofZWMOFswithoutthepresenceofadditionalanionsforchargecompensation.L1containsthreecarboxylategroupsattheterminalpositionsthatcanundergodeprotonation,completelyorpartially,andtherefore,cancoordinatetothemetalionsinvariouscoordi-nationmodesyieldingavarietyofinterestingframeworks.The–CH2–motiflinkingthepyridineandphenylringscanfreelyrotateintheassemblyprocesstomeetrequirementsofvariouscoordinationgeometries.TostudythestructuralinfluenceofligandL1ontheresultingframeworks,asimilarligand,H3L2Br=4-carboxy-1-(3,5-dicarboxybenzyl)pyridiniumbromide,wasusedtosynthesizeMOFsundermatchingreactionconditions(Fig.1).TothebestofourknowledgeonlytwostudieshavereportedMOFsdesignedthroughthispyridiniumbasedZWligandL2.32,33Maketal.usedL2tosynthesizethreefamiliesoflanthanidecoordinationpolymersluminescencebehaviorwhichcouldbetunedbydopingtheconcentrationoflanthanideions.32Lietal.studiedthephotolumin