2,2′-联吡啶为耦合单元的双自由基体系的理论研究

Theory study on biradical systems with 2,2′-bipyridyl as coupling unit

以2,2′-联吡啶为耦合单元,用·CH2,HNO·NH和·O四种自由基为自旋中心,设计出五种体系的分子.采用AM1-CI方法对其双自由基体系进行计算,结果表明,双自由基连接的位置不同对体系耦合作用的影响符合双自由基之间磁性耦合的拓扑规则,即共轭体系中,两个自由基之间以偶数碳(或氮)原子耦合,体系具有低自旋基态,表现为反铁磁耦合;两个自由基之间以奇数碳(或氮)原子耦合,体系具有高自旋基态,表现为铁磁耦合.

Spin coupling rules of ground state of 2,2′-bipyridyl as coupling unit and four radicals as spin centers have been studied by AM1-CI methods.It is proved that there are topological rules in magnetic coupling between radicals of conjugated systems.In conjugated system,the effective exchange integrals of radical sites through the even number of carbons with π-electron network are negative in sign,i.e,low spin state is stable ground state,while those through odd carbon atoms are positive in sign,i.e,high spin is stable ground state,