Effect of configuration and conformation on the spin multiplicity in xylylene type biradicals  

作　　者：张景萍 张宏 王立敏 王荣顺 王利祥 

机构地区：[1]Department of Chemistry, Northeast Normal University, Changchun 130024, China [2]State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China

出　　处：《Science China Chemistry》2000年第5期524-530,共7页中国科学（化学英文版）

摘　　要：The singlet-triplet splitting energy gap ΔEs-T= Es - ET is calculated for the ortho-, meta-, and para-xylylenes and their heteroatomic analogous by means of AM1-CI approach. It is shownthat when the radical centers R(R=H2C- ,H2N+- or HN’- ) are twisted sufficiently far out ofconjugation with the benzene ring, ΔEs-T tends to zero or is negative, i.e. ortho-, meta-, and para-phenylenes turn into weak ferromagnetic or antiferromagnetic coupling unit, while they are strong ferromagnetic (meta-isomers) or antiferromagnetic (ortho-, para-isomers) coupling units under planar conformation. It is suggested that serious twisted conformation is not recommended candidate for the design of novel high-spin molecules with stable high-spin ground states by ortho-or para-phenylene coupling unit.The singlet-triplet splitting energy gap ΔES-T=ES-ET is calculated for the ortho-, meta-, and para-xylylenes and their heteroatomic analogous by means of AM1-CI approach. It is shown that when the radical centers $R^. (R^. = H_2 C^. - ,H_2 N^{. + } - or HN^. - )$ are twisted sufficiently far out of conjugation with the benzene ring, ΔES-T tends to zero or is negative, i.e. ortho-, meta-, and para-phenylenes turn into weak ferromagnetic or antiferromagnetic coupling unit, while they are strong ferromagnetic (meta-isomers) or antiferromagnetic (ortho-, para-isomers) coupling units under planar conformation. It is suggested that serious twisted conformation is not recommended candidate for the design of novel high-spin molecules with stable high-spin ground states by ortho- or para-phenylene coupling unit.

关 键 词：high-spin molecule BIRADICAL xylylene AM1-CI twisted conformation 

分 类 号：O625[理学—有机化学]