Crystal Field Theory | Introduction to Chemistry

The Crystal Field Theory (CFT) is a model for the bonding interaction between transition metals and ligands. It describes the effect of the attraction ... Skiptomaincontent Interestedinteachingthiscourse? Lumencanhelp!Reviewourup-to-dateIntroduction to Chemistrybyclickingthelinkbelow.Fromthere,youcanrequestademoandreviewthecoursematerialsinyourLearning Management System (LMS). ReviewThisCourse Close IntroductiontoChemistry TransitionMetals Searchfor: CrystalFieldTheory   LearningObjective Discusstherelationshipsbetweenligandbindinginametalcomplexandthedegeneracyofthedorbitalsandbetweenthegeometryofametalcomplexandthesplittingofthedorbitals. KeyPoints Whentheligandsapproachthecentralmetalion,d-orf-subshelldegeneracyisbrokenduetothestaticelectricfield. Becauseelectronsrepeleachother,thedelectronsclosertotheligandswillhaveahigherenergythanthosefurtheraway,resultinginthedorbitalssplitting. Thecrystalfieldstabilizationenergy(CFSE)isthestabilitythatresultsfromligandbinding. Terms ligandAnion,molecule,orfunctionalgroupthatbindstoanotherchemicalentitytoformalargercomplex. degenerateHavingthesamequantumenergylevel. TheCrystalFieldTheory(CFT)isamodelforthebondinginteractionbetweentransitionmetalsandligands.Itdescribestheeffectoftheattractionbetweenthepositivechargeofthemetalcationandnegativechargeonthenon-bondingelectronsoftheligand.Whentheligandsapproachthecentralmetalion,thedegeneracyofelectronicorbitalstates,usuallydorforbitals,arebrokenduetothestaticelectricfieldproducedbyasurroundingchargedistribution.CFTsuccessfullyaccountsforsomemagneticproperties,colors,andhydrationenergiesoftransitionmetalcomplexes,butitdoesnotattempttodescribebonding. Theelectronsinthedorbitalsofthecentralmetalionandthoseintheligandrepeleachotherduetorepulsionbetweenlikecharges.Therefore,thedelectronsclosertotheligandswillhaveahigherenergythanthosefurtheraway,whichresultsinthedorbitalssplittinginenergy.Thissplittingisaffectedby: thenatureofthemetalion themetal’soxidationstate(ahigheroxidationstateleadstoalargersplitting) thearrangementoftheligandsaroundthemetalion thenatureoftheligandssurroundingthemetalion Allofthedorbitalshavefourlobesofelectrondensity,exceptforthedz2orbital,whichhastwoopposinglobesandadoughnutofelectrondensityaroundthemiddle.Thedorbitalscanalsobedividedintotwosmallersets.Thedx2–y2anddz2allpointdirectlyalongthex,y,andzaxes.Theyformanegset.Ontheotherhand,thelobesofthedxy,dxz,anddyzalllineupinthequadrants,withnoelectrondensityontheaxes.Thesethreeorbitalsformthet2gset.Inmostcases,thedorbitalsaredegenerate,butsometimestheycansplit,withtheegandt2gsubsetshavingdifferentenergy.TheCFTaccountsforthis. dorbitalsThisgivesanoverviewofthedorbitals.Thecentralmodelshowsthecombinedd-orbitalsononesetofaxes. Thecrystalfieldstabilizationenergy(CFSE)isthestabilitythatresultsfromplacingatransitionmetalioninthecrystalfieldgeneratedbyasetofligands.Itarisesduetothefactthatwhenthedorbitalsaresplitinaligandfield,someofthembecomelowerinenergythanbefore.Forexample,inthecaseofanoctahedron,thet2gsetbecomeslowerinenergy.Asaresult,ifthereareanyelectronsoccupyingtheseorbitals,themetalionismorestableintheligandfieldbytheamountknownastheCFSE.Conversely,theegorbitalsarehigherinenergy.So,puttingelectronsinthemreducestheamountofCFSE. OctahedralCFTsplittingElectrondiagramforoctahedraldshellsplitting. Crystalfieldstabilizationisapplicabletothetransition-metalcomplexesofallgeometries.Thereasonthatmanyd8complexesaresquare-planaristheverylargeamountofcrystalfieldstabilizationthatthisgeometryproduceswiththisnumberofelectrons. SquareplanarCFTsplittingElectrondiagramforsquareplanerdsubshellsplitting.   ShowSources Boundlessvetsandcurateshigh-quality,openlylicensedcontentfromaroundtheInternet.Thisparticularresourceusedthefollowingsources: “Boundless.” http://www.boundless.com/ BoundlessLearning CCBY-SA3.0. “degenerate.” http://en.wiktionary.org/wiki/degenerate Wiktionary CCBY-SA3.0. “ligand.” http://en.wiktionary.org/wiki/ligand Wiktionary CCBY-SA3.0. “GeneralChemistry/ShellsandOrbitals.” http://en.wikibooks.org/wiki/General_Chemistry/Shells_and_Orbitals Wikibooks CCBY-SA3.0. “Crystalfieldtheory.” http://en.wikipedia.org/wiki/Crystal_field_theory Wikipedia CCBY-SA3.0. “Octahedralcrystal-fieldsplitting.” http://en.wikipedia.org/wiki/File:Octahedral_crystal-field_splitting.png Wikipedia GNUFDL. “Dorbitals.” http://commons.wikimedia.org/wiki/File:D_orbitals.svg Wikimedia GNUFDL. “Squareplanar.” http://en.wikipedia.org/wiki/File:Square_planar.png Wikipedia GNUFDL. LicensesandAttributions CClicensedcontent,SharedpreviouslyBoundlessChemistry.Providedby:BoundlessLearning.Locatedat:https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/.License:CCBY-SA:Attribution-ShareAlike Previous Next