Ligand Field Theory - The Department of Chemistry, UWI ...

Ligand Field Theory can be considered an extension of Crystal Field Theory such that all levels of covalent interactions can be incorporated into the model. TheSpectrochemical Series OneoftheimportantaspectsofCFTisthatallligandsarenot identicalwhenitcomestocausingaseparationoftheenergyofthe d-orbitals.Fortransitionmetalcompounds,thereisclear evidenceforthisfromthemultitudeofcoloursavailablefora givenmetalionwhentheligandsorstereochemistryarevaried. Inoctahedralcomplexes,thiscanbeconsideredareflectionof theenergydifferencebetweenthehigherdz2, dx2-y2(egsubset)andthedxy, dyz,dxz(t2gsubset). Ithasbeenestablishedthattheabilityofligandstocausea largesplittingoftheenergybetweentheorbitalsisessentially independentofthemetalionandtheSPECTROCHEMICALSERIESisa listofligandsrankedinorderoftheirabilitytocauselarge orbitalseparations.ThushalidescauseasmallsplittingandCO givesalargesplitting. Ashortenedlistincludes: I-Cr>V-. Thiscannotbeexplainedonanionicbasisbutisconsistentwith theπbondingschemesincethegreaterthepositivechargeonthemetal, thelessreadilythemetalcandelocaliseelectronsbackintotheπ* orbitalsoftheCOgroup. NotethattheIRvalueswearedealingwithrelatetotheCObondand nottheM-CsowhentheCOfrequencygetslessthenitislosingtriplebond characterandbecomingmorelikeadoublebond.Thisisexpectedifelectronsare pushedbackfromthemetalintowhatwereemptyπ*antibondingorbitals. returntotheCHEM2101(C21J)course outline ReturntoChemistry,UWI-Mona, HomePage Copyright©2000-2010byRobertJohn Lancashire,allrightsreserved. CreatedandmaintainedbyProf.RobertJ. Lancashire TheDepartmentofChemistry,UniversityoftheWest Indies, MonaCampus,Kingston7,Jamaica. CreatedSeptember2000.Linkscheckedand/or lastmodified13thSeptember2010. URL http://wwwchem.uwimona.edu.jm/courses/LFT.html