以N—N基团为单桥的双核Cu(Ⅱ)体系磁-结构关联的理论研究

Theoretical Investigation on Magneto-Structural Correlation for Cu(Ⅱ) Binuclear System Bridged by Single N-N Group

在密度泛函理论的框架下 ,应用对称性破损方法 ,研究了以N—N基团为单桥的二嗪类双核Cu(Ⅱ )体系的磁耦合强度及磁 -结构关联 .计算结果表明 ,随着旋转角θ的减小 ,反铁磁性耦合作用逐渐减小 ,直至出现铁磁性耦合 ,与实验得到的趋势一致 .破损态能量随着θ的增大发生逆转 ,先降低后增大 .磁耦合常数J与 (ε1 -ε2 ) 2 的关系受到破损态能量逆转的影响 .当θ由 6 5°逐渐增大到 14 0°时 ,破损态能量依次降低 ,J与 (ε1 -ε2 ) 2 呈线性关系 ;当θ=15 0°时 ,破损态能量发生逆转 ,由降低变为升高 ,二者不再保持原有线性关系 .另外 ,(ε1 -ε2 ) 2 与θ的关系也受到破损态能量逆转的影响 .在θ=6 5°～ 14 0°范围内 ,J与θ以及 (ε1 -ε2 ) 2 与θ的图形相似 ,因此可用 (ε1 -ε2 ) 2 代替J讨论磁性与结构的关系 ;θ=15 0°时 ,二者图形不同 .破损态能量的逆转对磁耦合常数J的影响不大 ,而旋转角θ是影响磁耦合常数的关键因素 .

A theoretical study on magneto structural correlation for binuclear Cu(Ⅱ) complexes bridged by single N-N group from diazine has been investigated by using broken symmetry approach within the framework of density functional theory. Calculated results show that antiferromagnetic coupling interaction gradually reduces, and finally turns into ferromagnetic coupling interaction with the decrease of rotation angle θ around N-N bond from 150° to 65°, which is in agreement with the experimental facts. The variation of molecular energy has a reversion with rotation angle θ passing through 140°. The linear relationship between J and ( ε 1- ε 2) 2 is broken with the reversion of the energy of broken symmetry state from decrease to increase. This reversion of the energy of broken symmetry state also affects the relationship between ( ε 1- ε 2) 2 and θ . The figure for the relationship between J and θ is similar to that for the relationship between ( ε 1- ε 2) 2 and θ in the angle range θ =65°～140° where no reversion of the energy of broken symmetry state occurs. So in this angle range, ( ε 1- ε 2) 2 can replace J to explore the relationship between structure and magnetic properties. The reversion of the energy of broken symmetry state has little influence on the variation of J values, and rotation angle θ is a key factor influencing the magnitude of magnetic coupling interaction.