对吡啶的邻、间、对位的双自由基体系的理论研究

Theoretical study of biradical organic molecules with o,m,p-pyridine

针对以吡啶为耦合单元,以·CH2、·NH2+、HNO·和·NH 4种自由基为自旋单元的5种体系,采用密度泛函方法进行计算,得到了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个碳(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个碳(或氮)原子耦合,体系具有高自旋基态,表现为铁磁耦合．计算也说明,间位取代吡啶可以充当很好的铁磁耦合单元, 而邻位和对位取代吡啶不可以充当铁磁耦合单元．在2,6取代吡啶中以HNO·作自旋中心分子的高自旋基态有最稳定性,在3,5取代吡啶中以·NH作自旋中心分子的高自旋基态有最稳定性．

Novel stable high spin molecules are designed with ·CH2, HNO· ,· NH2 · ,· NH as a spin-containing（SC） fragment, and pyridine as a coupling（FC） unit. They have been studied by using DFT methods. It is proved that there are topological rules in magnetic coupling between radicals of conjugated systems： radical sites through the even number of carbons are conjugated, low spin state is stable ground state, the molecules corre- spond to antiferromagnetic coupling; while those through odd carbon atoms are conjugated, high spin state is stable ground state, the molecules correspond to ferromagnetic coupling. It shows m-pyridine can become ferro- magnetic coupling unit, and o,p-pyridine can not become ferromagnetic coupling. In 2,6-pyridine, the stability of high-spin ground states with NHO ~ as SC is highest, and that with· NH2^ ＋ as SC is lowest. In 3,5-pyri- dine, the stability of high-spin ground states with · NH as SC is highest, and that with· NH2 ^＋ as SC is lowest.