Systematic Approach To Design Organic Magnetic Molecules: Strongly Coupled Diradicals with Ethylene Coupler

Abstract

Theintramolecularmagneticcouplingconstant (J)valuesofdiradicalsystemslinkedwithtwomonoradicals throughacoupler(para-substitutedphenylacetylene(Model I),meta-substitutedphenylacetylene(ModelII),ethylene (ModelIII))wereinvestigatedbyunrestricteddensity functionaltheorycalculations.Wedividedeightmonoradicals intoα-groupandβ-groupaccordingtoMullikenspindensity valuesoftheconnectedatoms.Theoveralltrendsinthe strengthofmagneticinteractionsofdiradicalswerefoundto beidenticalinthreedifferentmodelsystems.Thediradicals withpara-substitutedphenylacetylenecouplerresultedin almosttwicestrongerintramolecularmagneticcoupling interactionsofthecorrespondingdiradicalsascomparedtothemeta-substitutedonewithoppositemagnetism.NNEthylene- PO(nitronylnitroxideradicalcoupledtophenoxylradicalviaethylenecoupler)wascalculatedtohavethestrongest magneticcouplingconstantwithferromagnetism,andtobeevenstronger(morethantwice)thanNN-ethylene-NN(nitronyl nitroxidediradicalwithethylenecoupler),whichwasreportedtohavestrongantiferromagneticinteractionsinaprevious experiment.Itwasfoundthatthespindensityvaluesoftheconnectedatomsarecloselyrelatedtothedeterminationofmagnetic interactionsandJvalues.Thespinstatesofthegroundstateindiradicalsystemswereexplainedbymeansofthespinalternation rule.