构象对同位乙烯双自由基体系基态自旋多重度及其稳定性影响的理论研究  

Theoretical Studies on Effect of Conformation on the Spin Multiplicity Ground State in Parity Ethylene Type Biradical System and Stability

作　　者：王立敏[1] 张景萍[1] 玄玉实[1] 王荣顺[1] 

机构地区：[1]东北师范大学化学学院,长春130024

出　　处：《高等学校化学学报》2004年第5期913-916,共4页Chemical Journal of Chinese Universities

基　　金：国家自然科学基金 (批准号 :2 980 40 0 2 ;2 0 2 740 0 6);霍英东青年教师基金(批准号 :710 13 );东北范师大学校内青年基金(批准号 :1114 3 4)资助

摘　　要：用 DFT,CASSCF和 QCISD( T)方法 6-3 1 G*基组计算了构象对同位二取代乙烯双自由基体系基态自旋多重度及其稳定性的影响 .结果表明 ,用 DFT或 CASSCF方法计算的单、三重态的能量差随自由基与乙烯间的二面角增加成不规则变化 ;用 QCISD( T)方法计算的单、三重态的能量差随二面角的增加而逐渐降低 ,并呈规律性变化 ,说明 QCISD( T)方法用于计算分子的磁性是可信的 .对于同位二取代乙烯双自由基体系 ,无论双自由基旋转 ,还是单自由基旋转 ,高自旋基态稳定性随自由基与乙烯间二面角的增加而降低 ,只是降低的幅度不同 ,当二面角接近 90°时 ,同位乙烯由具有平面或近似平面构象时强的铁磁耦合单元变成接近垂直平面构象时弱的反铁磁耦合单元或弱的铁磁耦合单元 .The effect of conformation on the spin multiplicity of ground state and it′s stability were investigated for parity ethylene type biradical system by means of comparative study with DFT, CASSCF and QCISD(T) methods. It is found that based on the continuous twisting of radical centers out of conjugation with the ethylene, both the absolute values and the tendency for the stability of triplet ground state (ΔE S-T) of the investigated system change dramatically with variation the calculation methods. DFT and CASSCF methods cannot give a smooth change for ΔE S-T, when the radical centers in the ethylene are twisted. However, the ΔE S-T result obtained by QCISD(T) method offers a smooth change in the continuous twisting of radical centers. It is suggested that QCISD(T) method is reliable for dealing with the conformational problem of high-spin molecules. Furthermore, the ΔE S-T values for ethylene type biradicals with one and two twisted radical centers were explored, respectively. When two or one radical centers in the ethylene are twisted sufficiently out of conjugation, and dihedral angles are close to 90°, ethylene turns into a weak antiferromagnet and weak ferromagnetic coupling units, respectively. Though the ethylene is a robust ferromagnetic coupling unit under planar conformation.

关 键 词：同位乙烯 双自由基体系 基态自旋多重度 稳定性 构象 

分 类 号：O623.121[理学—有机化学] O641[理学—化学]