搜索
1ElectronSpinResonance(ESR)Spectroscopyappliedtospecieshavingoneormoreunpairedelectrons:freeradicals,biradicals,othertripletstates,transitionmetalcompoundsspecieshavingoneunpairedelectronhastwoelectronspinenergylevels:E=gmBBoMsselectionruleDMs=±1==DE=gmBBog:proportionalityconstant,2.00232forfreeelectron1.99–2.01forradicals1.4–3.0fortransitionmetalcompoundsinisotropicsystems(gas,liquidorsolutionoflowviscosity,solidsiteswithsphericalorcubicenvironment),gisindependentoffielddirectionmB:Bohrmagneton9.274x10-24JT-1forelectronMS:electronspinquantumnumber+1/2or–1/2化妆品–1.24T==correspondingfrequency9.5(X-band)–35(Q-band)GHztheelectroninteractswithaneighboringnuclearmagneticdipole,theenergylevelsbecome:E=gmBBoMS+amBMSmImI:nuclearspinquantumnumberfortheneighboringnucleusa:hyperfinecouplingconstantenergylevelsandtransitionsforasingleunpairedelectroninanexternalmagneticfieldwithnocouplingcouplingtoonenucleuswithspin1/23spin-latticerelaxation:microwaveradiationtransferredfromthespinsystemtoitssurroundingslongrelaxationtime==decreaseinsignalintensityshortrelaxationtime==resonancelinesbecomewidetypicalESRspectrometer—aradiationsource(klystron)asamplechamberbetweenthepolesofamagnetadetectionandrecordersystemESRspectrum(a)absorptioncurve(b)first-derivativespectrumstandard:DPPH(diphenylpicrylhydrazylradical)g=2.0036,pitchg=2.0028Bstdgsample=gstd———Bsampleforfield-sweep,lowerfield(left-hand)thanstandard,highergvalue4hyperfinecouplinginisotropicsystemsinteractionsbetweenelectronandnuclearspinmagneticmoments==finestructureinESRspectrumcouplingsariseintwoways:(i)directdipole-dipoleinteraction(ii)FermicontactinteractioncouplingpatternsinESRaredeterminedbythesamerulesthatapplytoNMRcouplingtonucleiwithspin1/2aremorefrequentlyobservedhyperfinecouplingconstantgmBMHzorcm-1hyperfinesplittingconstantAgaussormillitelsla•dependsontheunpairedelectronspindensityatthenucleusinquestion•isrelatedtothecontributiontotheatomofthemolecularorbitalcontainingtheunpairedelectron•unpairedelectroncanpolarizethepairedspinsinanadjacentsbond==thereisunpairedelectronspindensityatbothnuclei5Ex.1[C6H6•]-couplingtoall6Hatomstheelectronisdelocalizedoverall6CatomsEx.2pyrazineradicalanion(a)couplingto214Nnuclei(1:2:3:2:1quintet),andsplitby4Hatomsfurtherinto1:4:6:4:1quintet(b)Na+salt,furthersplittinginto1:1:1:1quartet6Ex.3BH4-+•C(CH3)3[BH3•]-+HC(CH3)3Ex.4NBut┐•+S(=NBut)2+Me2SiCl2SSiMeNButg=2.005A(N)=0.45mT7Ex.5S(=NBut)2•-g=2.0071A(N)=0.515mTEx.6(MeO)3PBH2•8Ex.7CrIII(porphyrin)Cl•thepatternsofhyperfinesplittingsprovidedirectinformationaboutthenumbersandtypesofspinningnucleicoupledtotheelectrons•themagnitudesofthehyperfinecouplingsindicatetheextenttowhichtheunpairedelectronsaredelocalized,gvaluesshowwhetherunpairedelectronsarebasedontransitionmetalatomsoronadjacentligands.9zero-fieldsplittingintheabsenceofmagneticfield,2S+1energystatessplitdependsonthestructureofsample,spin-orbitcouplingtheappearanceofmorethanoneline(S1/2)finestructure--inprinciple,2Stransitionscanoccur,theirseparationsrepresentingtheextentofzero-fieldsplitting10anisotropicsystemssolids,frozensolutions,radicalspreparedbyirradiationofcrystallinematerials,radicaltrappedinhostmatrices,paramagneticpointdefectinsinglecrystalsforsystemswithsphericalorcubicsymmetrygfactorsforsystemswithlowersymmetry,g==g‖andg┴==gxx,gyy,gzzESRabsorptionlineshapesshowdistinctiveenvelopesystemwithanaxisofsymmetrynosymmetry11Ex.8Li+–13CO2-inCO2matrixlarge13Candsmall7Li(I=3/2)hyperfinesplittingEx.9HMn(CO)5/solidKrmatrixat77Khu－→•Mn(CO)5A‖(55Mn)=6.5mTA┴(55Mn)=3.5mTA┴(83Kr)=0.4mT12transitionmetalcomplexes•thenumberofdelectrons•highorlowspincomplex•consequenceofJahn-Tellerdistortion•zero-fieldsplittingandKramer’sdegeneracyESRspectraofsecondandthirdrowtransitionmetalcomplexesareoftenhardtoobserved,however,rare-earthmetalcomplexesgiveclear,usefulspectrashortspin-latticerelaxationtimes==broadspectrallineslowtemperatureexperimentswillbeneededtoobservespectraEx.10d3system13trans-[Cr(pyridine)4Cl2]+(a)frozensolutioninDMF/H2O/MeOH(b)intrans–[Rh(pyridine)4Cl2]Cl·6H2OpowderEx.11d6systemlow-spindiamagneticOhtetragonalhigh-spin5D－→5T2－－－→5B2shortrelaxationtimes==broadresonanceslargezero-fieldsplittings==noresonanceobserved14Ex.12d9systemCuII(TPP)complex(frozensolutioninCCl3H)Cu(acac)2frozensolution15multipleresonanceENDOR(electron-nucleardoubleresonance)Ex.13[Ti(C8H8)(C5H5)]intoluene(frozensolution)(a)ESRspectrum(b)1HENDORspectrum1617