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STRUCTURESANDMAGNETICPROPERTIESOFLOW-DIMENSIONALSALTS By LIANG-KUEICHOU ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1996 ACKNOWLEDGMENTS WhenIarrivedinGainesvilleinAugust1991,thefirstEnglishIlearnedwas, "Go,Gators!". IhavelivedinGainesvillelongerthananywhereelse,exceptmyhome town,Taipei. Imustthankthechemistrydepartmentforgivingmethechancetocomehere notonlystudychemistry,buttounderstandAmerica'sphilosophyonlife. IhopethatItoo havemadeasmallcontributiontothequalityreputationoftheDepartmentofChemistryat theUniversityofFlorida. Ihavegreatappreciationfortheguidanceandsupportofmyresearchdirector,Dr. DanielR.Talham. FromDan,Ihavenotonlybeguntolearnthefunofchemistry,butthe attitudeofdiscoveringandsearchingfornewthingsinscience. Ithankthemembersofmycommittee,ProfessorsRussellS.Drago,JamesM. Boncella,WilliamR.Dolbier,andMarkW.Meisel,fortheirtime,adviceand ecouragement. Theresearchofthisdissertationisgreatlydependentontheassistanceand manyhelpfulconversationswithDrs.KhalilAbboud,ManuelA.QuijadaandW.W.Kim. Onecanlearnmuchfromthepeoplearoundone,andmyfellowgroupmembers overtheyearshavemadethatalltooevident. Thosewhohavemaderesearchsoenjoyable areGlennisondeOliveira,MarvinClevenger,BrianWard,ScottWhipps,CandaceSeip, GailFanucciandMelissaPetruska. Ialsothankmyfriend,Hsiang-LinLiuandGarretE. Granroth,whohelpedmealotinunderstandingsolid-statetheory. Myparents,Chao-FengandChun-Chih,supportmeallthetime. Itreallyhelpsme alot,wheneverIgetacallfromtheminTaiwan. WheneverIfacedifficulties,theyalways say"Hey,Chou,youhavealreadywashedyourheadhalfway,goaheadtofinishit." FinallyIthankmywife,Yu-chi. SinceImetherin1986,shehasalways accompaniedmeineverythingIdo,evenanNMRexperiment. WheneverIhaveadifficult timewithanexperiment,shealwaysencouragesmeandtellsme"Don'tgiveup." iii TABLEOFCONTENTS ACKNOWLEDGMENTS ii ABSTRACT vi CHAPTERS 1 BACKGROUND AND INTRODUCTION 1 One-Dimensional Heisenberg Antiferromagnets 1 Organic Cation-Radical Salts 10 2 SYNTHESIS,STRUCTUREANDMAGNETICSUSCEPTIBILITYOF TETRAMETHYLAMMONOIUMNICKELNITRITE, A(CNHT3)I4FNE[NRiR(NO0M2)A3]G:NAENTS=1ONE-DIMENSIONALHEISENBERG 19 Experimental Section 20 SynthesisofTetramethylammoniumNickelNitrite(TMNIN) 20 CrystallographicDataCollectionandStructureDetermination 20 Magnetic Measurements 21 ResultsandDiscussion 22 TMNINStructure 22 Magnetic Susceptibility 27 Conclusions 30 3 THESYNTHESIS,STRUCTURE,MAGNETICSUSCEPTIBILITY ANDSOMEPHYSICALCHARACTERISTICSOF Ni(C3HioN2)2N3(C104),NINAZ 31 Experimental Section 33 TheSynthesisof&w(propylenediamine)azidonickel(II)perchlorate 33 Ultra-fine Powder NINAZ 43 Magnetic Measurements 43 ESRMeasurements 46 Elemental Analysis 46 ResultsandDiscussion 47 NINAZStructure 47 Haldane Gap in NINAZ-d2o 52 Magnetic Susceptibility 52 ESRResult 55 Conclusions 68 iv 4 DICATIONSALTSOFTHEORGANICDONOR BIS(ETHYLENEDITfflO)TETRATHIAFULVALENE 71 Experimental Section 72 Materials 72 BEDT-TTF(BF4)2 73 BEDT-TTF(C104)2 76 CrystallographicDataCollectionandStructureDetermination 76 OpticalMeasurement 77 ResultsandDiscussion 78 SynthesisandStructure 78 OpticalProperties 85 Conclusions 85 5 STRUCTURE,MAGNETIC,OPTICAL,ANDTRANSPORT PROPERTIESOF(BEDT-TTF)PF6* 91 Introduction 91 Experimental Section 93 Materials 93 (BEDT-TTF)PF6*,S-(BEDT-TTF)PF6,ande-(BEDT-TTF)PF6 93 CrystallographicDataCollectionandStructureDetermination 93 Temperature-dependentESRExperiment 95 TransportMeasurement 96 OpticalMeasurement 97 MagneticMeasurement 98 Results 98 SynthesisandStructure 98 OpticalMeasurement 99 Conductivity 110 ESRMeasurement 115 MagneticSusceptibilityMeasurement 120 Discussion 120 Structure 120 MagneticData 123 Conclusions 123 APPENDK 124 TABLES OF CRYSTALLOGRAPHIC DATA 125 LISTOFREFERENCES 154 BIOGRAPHICALSKETCH 160 v AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy STRUCTURESANDMAGNETICPROPERTIESOFLOW-DIMENSIONALSALTS By Liang-KueiChou May,1996 Chairman: DanielR.Talham MajorDepartment: Chemistry Thisdissertationpresentsexperimentalresultsfromthesynthesis,structure determination,magnetic,andelectronicpropertiescharacterizationsoftwotypesoflow- dimensionalsalts. Thefirstclassofmaterialsareone-dimensionalnickel(H)chain compounds,andthesecondtypeofmaterialsareBEDT-TTFcation-radicalsalts. The crystalstructureoftetramethylammoniumnickelnitrite,(CH3)4N[Ni(N02)3](TMNIN)was determinedbyX-raydiffractionatroomtemperature. ThestructureofTMNINconsistsof infinitechainsofNi2+ionswithadjacentNi2+ionsbridgedbythreecis-jx-nitroligands. AlternateNi2+ionsalongthechainarechemicallydistinctwithNiloctahedrally coordinatedwithsixnitritenitrogens,andtheadjacentNi2isoctahedrally coordinatedwith sixnitriteoxygens. Thetetramethylammoniumionsarelocatedinpositionsalongthe3- foldrotationaxesandformchannelsthatseparatetheNichains. Fromthemagnetic susceptibilitydata,TMNTNisidentifiedasaone-dimensionalHeisenbergantiferromagnet. ThedataareinterpretedinthecontextofHaldaneGapmaterials. B/s(propylenediarnine)azidonickel(II)perchlorate,Ni(C3HioN2)2N3(C104) vi (NINAZ)isanotherquasi-one-dimensionalchaincompound. Thesyntheticmethodto NINAZhasbeenimprovedandlargepuresinglecrystals(1.5cmX1.5cmX0.2cm) havebeenobtained. DeuteratedNINAZhasalsobeensynthesizedinordertomeasurethe HaldaneGapwithneutroninelasticscattering. Themagneticpropertiesasafunctionof particlesizehavebeeninvestigated. Dicationsaltsoftheorganicdonorftw(ethylenedithio)tetrathiafulvalene(BEDT- TTF)havebeenisolatedasBF4"andCIO4"salts. Theyarethefirstexamplesofsalts whereBEDT-TTFappearsonlyasdication. BondlengthdatafromX-raystructure determinationsofthedicationsaltswereusedasstandardsforassigningthe+2oxidation statetoBEDT-TTFmoleculesinmixedvalencecation-radicalsalts. Opticalspectroscopy showsthatduringtheelectrocrystallizationBEDT-TTFisslowlyoxidizedbyCICH2COCI, indicating(BEDT-TTF)+isfirstformedintheelectrolyticmediumbeforeelectrochemical oxidationtothedicationandprecipitationwiththeelectrolyteanion. Thenewcompound(BEDT-TTF)PF6*hasalsobeenpreparedby electrocrystallizationmethods,andthecrystalstructurewasdeterminedbyX-ray diffractionatroomtemperatureand173K. Unlikeasimilarsalt,5-(BEDT-TTF)PF6,there isnodimerizationofthedonormoleculesatroomtemperaturein(BEDT-TTF)PF6*. A structuralphasetransitionat260Khasbeenassignedtoanionordering. Fromthe conductivity,ESRandopticaldata,weconcludethat(BEDT-TTF)PF6* isaMott- Hubbardinsulator. Alowtemperaturemagnetictransitionisdiscussedintermsofa spin-Peierlstransition. vii . CHAPTER BACKGROUNDANDIN1TRODUCTION Thisdissertationpresentstheexperimentalresultsfromthesynthesis,structure determination,magnetic,andelectronicpropertiescharacterizationsoftwotypesoflow- dimensionalsalts. Thefirstareone-dimensionalnickel(II)chainmaterials,andthesecond typeofmaterialisBEDT-TTFcation-radicalsalts. Chapter1willprovidealiterature reviewonthequasi-one-dimensionalS=l/2andS=lchaincompoundsandcation-radical molecularsolidsbasedonbis(ethylenedithio)tetrathiafulvalene(BEDT-TTF). Chapter2 willdescribethesynthesis,structureandmagneticsusceptibilityoftetramethylammonium nickelnitrite(TMNIN),(CH3)4N[Ni(N02)3],anS=lone-dimensionalHeisenberg antiferromagnet. Chapter3willdescribethesynthesis,structure,andmagneticproperties ofb/s(propylenediamine)azidonickel(II)perchlorate(NINAZ)Ni(C3HioN2)2N3(C104) Chapter4willpresentthesynthesis,structures,andopticalpropertiesofdicationsaltsof BEDT-TTF. Chapter5willpresentthesynthesis,structures,conductivities,and temperature-dependentESRmeasurementsof(BEDT-TTF)PF6*andS-(BEDT-TTF)PF6. One-DimensionalHeisenbergAntiferromagnets Thechemicalrealizationofquasi-one-dimensional(quasi-ID)materialshasallowed fordetailedexperimentalinvestigationsprobingthephysicaltheoriesthatdescribe electronicandmagneticpropertiesinlow-dimensionalsolids.1 Anunderstandingof physicalphenomenainquasi-IDsolidshasledtothedevelopmentofanumberof conducting,2superconducting,3andmagneticmaterials4basedonlow-dimensional 1 2 structures. In1983,Haldanesuggested5that aone-dimensionalHeisenberg antiferromagnet(IDHAF)withintegerspinpossessedanenergygapbetweenthe nonmagneticgroundstateandthefirstexcitedstate. Innonintegerspinsystems,thereis noenergygapbetweenthegroundstateandfirstexcitedstate. Themagneticsusceptibility behaviorofS=l/2andS=lone-dimensionalHeisenbergsystemsareverydifferent. The susceptibilityresultsforaspinS=l/2Heisenberglinearchainhavebeendescribedby BonnerandFisher.6 Abroadmaximuminthesusceptibilityispredicted,asillustratedin Figure1.1. ForS=l/2,thesusceptibilitymaximumwillhavevalue —X—max =0.07346 NgV /IJI atthetemperature kTmax/|j| = 1.282 AccordingtoBonnerandFishertheory,whenthetemperatureapproaches0K,the susceptibilityof(S=l/2)nonintegersystemswillhavefinitevalue. Thistheoryhasbeen appliedtoaverylargenumberofsamples;7 forexample,fitsofthesusceptibilitiesof [Cu(NH3)4](N03)28areshowninFigure1.2. Anotherexampleofanantiferromagnetic Heisenbergchaincompound(S=noninteger)is[N(CH3)4]MnCl3,TMMC,thestructure9 ofwhichisillustratedinFig.1.3. ThecrystalconsistsofchainsofS=5/2manganese atomsbridgedbythreechlorideions;theclosestdistancebetweenmanganeseionsin differentchainsis0.915nm. TheintrachainexchangeconstantJ/kisabout-6.7K. Intheintegerspin(S=1,2)Heisenbergsystems,asthetemperatureapproachesabsolute zeroK,thesusceptibilitiesapproachtozero. Todate,thefewsystemsthatarebelievedto beHaldanematerialsincludetheNi2+linearchaincompounds[Ni(C2HgN2)2N02]C104