Singlet-triplet gap in triplet ground-state biradicals is modulated by substituent effects
Singlet-triplet gap in triplet ground-state biradicals is modulated by substituent effects
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DOI：
10.1021/ja020154
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发表时间：
2002-08-28
影响因子：
15
通讯作者：
Rheingold, AL
中科院分区：
文献类型：
--
作者：
Shultz, DA;Bodnar, SH;Rheingold, AL
合成了三种S = 1双（半醌）配合物。为了确保分子内的铁磁性交换耦合，两个半醌被1，3连接到5-取代的亚苯基环上。双自由基配合物的不同在于它们的间位取代基：1-NMe 2，X=N，N-二甲氨基; 1-t-Bu，X =叔丁基; 1-NO2，X =硝基。所有三种结构都已通过X射线晶体学确定。结构研究结果表明，三种配合物的双自由基配体具有几乎相同的构象，其半醌环相对于5-取代亚苯基环的平均扭转度为32 ° ± 2 °。交换参数J（H）= -2J（S）。(S)盖（2）上），范围从1-NO2的+31.0 +/- 0.6 cm（-1）到1-t-Bu的+59.3 +/- 1.2 cm（-1），1-NMe 2的J = +34.9 +/-0.7 cm（-1）。由于构象几乎相同，交换耦合参数J的差异是由于取代基效应。实验结果得到了Huckel理论和前人计算工作的支持。
Three S = 1 bis(semiquinone) complexes have been prepared. To ensure ferromagnetic intramolecular exchange coupling, the two semiquinones are attached 1,3 to a 5-substituted phenylene ring. The biradical complexes differ in their meta-substituents: 1-NMe2,X=N,N-dimethylamino; 1-t-Bu, X = tert-butyl; 1-NO2, X = nitro. All three structures have been determined by X-ray crystallography. Results of structural studies indicate that the biradical ligands of all three complexes have nearly identical conformations with average semiquinone ring torsions of 32degrees +/- 2degrees relative to the 5-substituted phenylene ring. The exchange parameter, J (H = -2J (S) over cap (1).(S) over cap (2)), ranges from +31.0 +/- 0.6 cm(-1) for 1-NO2 to +59.3 +/- 1.2 cm(-1) for 1-t-Bu, with J = +34.9 +/-0.7 cm(-1) for 1-NMe2. Since the conformations are nearly identical, the differences in exchange coupling parameter J are due to substituent effects. The experimental results are supported by Huckel theory arguments and previous computational work.